Patent Application
20130076861
The present application draws priority from Israel Patent Application IL 203449 filed on Jan. 21, 2010 and is a continuation-in-part of U.S. application Ser. No. 13/010,810 filed on Jan. 21, 2011. The present application is a continuation-in-part of PCT/IL2011/000075 filed on Jan. 23, 2011—PCT/IL2011/000075 is incorporated herein by reference in its entirety.
The present disclosure relates to techniques and apparatus for probing an object(s), medium(s) or optical path using noisy light.
The following patents, patent applications and non-patent publications may be of interest. The disclosures of all patents and patent applications on the list below, and mentioned anywhere in the present disclosure, are hereby incorporated by reference:
[1] U.S. Pat. No. 6,392,585, Huff et al, “Random noise radar target detection device”, May 21, 2002.
[2] U.S. Pat. No. 6,864,834, Walton, “Radar system using random RF noise”, Mar. 8, 2005.
[3] T. Thayaparan and C. Wernik, “Noise radar technology basics”, Technical memorandum of Defense Research and Development, DRDC Ottawa TM 2006-266, December 2006
[4] Jiang et al, “Low coherence fiber optics for random noise radar”, in the MILCOM 2000—21st Century Military Communications Conference Proceedings, pp. 907-911 (2000)
[5] U.S. Pat. No. 5,034,678, Eichen et al, “Method of and apparatus for measuring the frequency response of an electrooptic device using an optical white noise generator”, Jul. 23, 1991.
[6] WO 2009/098694, Granot and Sternklar, “Methods and devices for analyzing material properties and detecting objects in scattering media”, Aug. 13, 2008.
[7] U.S. Pat. No. 7,505,135, Granot and Sternklar, “Method and apparatus for imaging through scattering or obstructing media”, Mar. 17, 2009.
It is now disclosed a method of optically probing an object(s) and/or a medium and/or an optical path including the object(s) or medium, the method comprising: a) illuminating the object(s) or the medium to induce, from the object(s) or medium, one or more noisy light response signals that are randomly or pseudo-randomly modulated; b) receiving into an optical detector an optical superimposition of (i) a noisy source light signal used in step (a) to carry out the illuminating and (ii) one or more of the induced noisy light response signals, thereby illuminating the optical detector so as to generate a combination electrical signal describing the optically superimposed plurality of received noisy light response signals; c) determining or characterizing or detecting from the combination electrical signal, at least one of: i) a relationship between power and frequency of the combination electrical signal or a derivative thereof over a discrete or continuous spectrum; ii) a temporal autocorrelation function of the combination electrical signal; iii) a distance parameter(s) involving one or more the objects; iv) a mechanical stress or strain; v) a change in a light propagation time of at least one optical path; vi) a difference in light propagation times of multiple optical paths or a temporal change thereof; vii) mechanical motion of an object; and viii) a material or mechanical property of an optical fiber, at least a portion of which is included in the optical path of step (a).
It is now disclosed a method of optically probing an object(s) and/or a medium and/or an optical path including the object(s) or medium, the method comprising: a) illuminating the object(s) or the medium to induce, from the object(s) or medium, a plurality of noisy light response signals that are randomly or pseudo-randomly modulated, each induced noisy light response signal of the optical superimposition being associated with a different respective target location of the object(s) or medium and with a different respective target-location-including optical path; b) receiving into an optical detector an optical superimposition of the plurality of the noisy light response signals so as to illuminate the optical detector and to generate a combination electrical signal describing the optically superimposed plurality of received noisy light response signals; c) determining or characterizing or detecting from the combination electrical signal, at least one of: i) a relationship between power and frequency of the combination electrical signal or a derivative thereof over a discrete or continuous spectrum; ii) a temporal autocorrelation function of the combination electrical signal; iii) a distance parameter(s) involving one or more the objects; iv) a mechanical stress or strain; v) a change in a light propagation time of at least one optical path; vi) a difference in light propagation times of multiple optical paths or a temporal change thereof; vii) mechanical motion of an object; and viii) a material or mechanical property of an optical fiber, at least a portion of which is included in the optical path of step (a).
In some embodiments, step (c) or a portion thereof is contingent upon the sub-signals of the combination electrical signal sharing substantially the same noise-driven temporal fluctuations.
In some embodiments, the relationship between power and frequency is determined or characterized or detected.
In some embodiments, the temporal autocorrelation function is determined or characterized or detected.
In some embodiments, the distance parameter(s) is determined or characterized or detected.
In some embodiments, the change in a light propagation time of the at least one optical path is determined or characterized or detected.
In some embodiments, the difference in light propagation times of multiple optical paths or a temporal change thereof is determined or characterized or detected.
In some embodiments, the mechanical motion of the object is determined or characterized or detected.
In some embodiments, the object is a person or animal or moving vehicle.
In some embodiments, the optical fiber material or mechanical property is determined or characterized or detected.
In some embodiments, the optical superimposition of the plurality of noisy light response signals includes: a) first noisy light signal associated with a first target location and a first of the target-location-including optical paths; and ii) a second of the noisy light response signals associated with a second target location and a second of the target-location-including optical paths, the second target location being separated from the first target location by at least 1 mm.
In some embodiments, the noisy light response signal(s) include ultraviolet or visible light.
In some embodiments, the noisy light response signal(s) include infra-red light.
In some embodiments, the noisy light response signal(s) include near infra-red (NIR) light.
In some embodiments, at least one target-location-including optical path is primarily within an optical fiber.
In some embodiments, at least one target-location-including optical path is primarily free space.
In some embodiments, a source of the illumination is aimed from a moving vehicle and/or at a moving vehicle.
In some embodiments, the method includes analyzing noise patterns of the combination electrical signal or of a derivative thereof.
In some embodiments, step (c) or a portion thereof is carried out in accordance with the results of the analysis of the noise patterns.
In some embodiments, the source signal used in step (a) to carry out the illuminating is a noisy source signal.
In some embodiments, the source signal used in step (a) to carry out the illuminating is not a noisy source signal.
In some embodiments, a bandwidth of the optical detector exceeds a noise bandwidth of one or more of noisy light signals of the optical superimposition received therein.
A “bandwidth” and “speed” of the optical detector reflects the characteristic time constants of optical detector electronics which converts the light signal received by the detector into an electrical signal descriptive of the light signal received by the detector
In some embodiments, a bandwidth of the optical detector exceeds a noise bandwidth of one or more of noisy light signals of the optical superimposition received therein by at least a factor of 10, or at least a factor of 100, or at least a factor of 1000.
In some embodiments, a bandwidth of the optical detector exceeds a noise bandwidth of one or more of noisy light signals of the optical superimposition received therein by at least a factor of 100.
In some embodiments, a bandwidth of the optical detector exceeds a noise bandwidth of one or more of noisy light signals of the optical superimposition received therein by at least a factor of 1,000.
In some embodiments, a noise bandwidth of one or more of noisy light signals of the optical superimposition exceeds a bandwidth of the optical detector.
In some embodiments, a noise bandwidth of one or more of noisy light signals of the optical superimposition exceeds a bandwidth of the optical detector by at least a factor of 10, or at least a factor of 100, or at least a factor of 1000.
In some embodiments, a noise bandwidth of one or more of noisy light signals of the optical superimposition and/or a bandwidth of the optical detector is less than 50 GHz or less than 10 GHz or less than 1 GHz or less than 100 MHz.
In some embodiments, the source signal used in step (a) to carry out the illuminating is a noisy source signal having a noise bandwidth selected in accordance with a desired depth resolution.
It is now disclosed apparatus for optically probing an object(s) and/or a medium and/or an optical path including the object(s) or medium, the apparatus comprising: a) a source of light configured to illuminate the object(s) or the medium to induce, from the object(s) or medium, one or more noisy light response signals that are randomly or pseudo-randomly modulated; b) an optical detector configured to receive an optical superimposition of (i) a noisy source light signal used in step (a) to carry out the illuminating and (ii) one or more of the induced noisy light response signals, thereby illuminating the optical detector so as to generate a combination electrical signal describing the optically superimposed plurality of received noisy light response signals; c) electronic circuitry configured to determine or characterize or detect from the combination electrical signal, at least one of: i) a relationship between power and frequency of the combination electrical signal or a derivative thereof over a discrete or continuous spectrum; ii) a temporal autocorrelation function of the combination electrical signal; iii) a distance parameter(s) involving one or more the objects; iv) a mechanical stress or strain; v) a change in a light propagation time of at least one optical path; vi) a difference in light propagation times of multiple optical paths or a temporal change thereof; vii) mechanical motion of an object; and viii) a material or mechanical property of an optical fiber, at least a portion of which is included in the optical path of step (a).
It is now disclosed apparatus for optically probing an object(s) and/or a medium and/or an optical path including the object(s) or medium, the apparatus comprising: a) a source of light configured illuminate the object(s) or the medium to induce, from the object(s) or medium, a plurality of noisy light response signals that are randomly or pseudo-randomly modulated, each induced noisy light response signal of the optical superimposition being associated with a different respective target location of the object(s) or medium and with a different respective target-location-including optical path; b) an optical detector configured to receive an optical superimposition of the plurality of the noisy light response signals so as to illuminate the optical detector and to generate a combination electrical signal describing the optically superimposed plurality of received noisy light response signals; c) electronic circuitry configured to determine or characterize or detect from the combination electrical signal, at least one of: i) a relationship between power and frequency of the combination electrical signal or a derivative thereof over a discrete or continuous spectrum; ii) a temporal autocorrelation function of the combination electrical signal; iii) a distance parameter(s) involving one or more the objects; iv) a mechanical stress or strain; v) a change in a light propagation time of at least one optical path; vi) a difference in light propagation times of multiple optical paths or a temporal change thereof; vii) mechanical motion of an object; and viii) a material or mechanical property of an optical fiber, at least a portion of which is included in the optical path of step (a).
In some embodiments, the source of light is a source of noisy light.
In some embodiments, the light produced by the light source is not noisy light.
In some embodiments, the electronic circuitry includes any combination of analog electronics, digital electronics and computer code/software.
It is now disclosed a method of optically probing an object(s) and/or a medium and/or an optical path including the object(s) or medium, the method comprising: a) illuminating the object(s) or the medium to induce, from the object(s) or medium, one or more of noisy light response signals that are randomly or pseudo-randomly modulated; b) simultaneously receiving into an optical detector an optical superimposition of at least one of: i) a plurality of the noisy light response signals, each induced noisy light response signal associated with a respective target location of the object(s) or medium and with a different respective target-location-including optical path; ii) a noisy source light signal used in step (a) to carry out the illumination and to induce one or more of the noisy light response signals, so as to illuminate the optical detector and to generate a combination electrical signal describing the optically superimposed plurality of received noisy light response signals; and c) determining or characterizing or detecting from the combination electrical signal, at least one of: i) a relationship between power and frequency of the combination electrical signal or a derivative thereof over a discrete or continuous spectrum; ii) a temporal autocorrelation function of the combination electrical signal; iii) a distance parameter(s) involving one or more the objects; iv) a mechanical stress or strain; v) a change in a light propagation time of at least one optical path; vi) a difference in light propagation times of multiple optical paths or a temporal change thereof; vii) mechanical motion of an object; and viii) a material or mechanical property of an optical fiber, at least a portion of which is included in the optical path of step (a).
In some embodiments, step (c) or a portion thereof is contingent upon the sub-signals of the combination electrical signal sharing substantially the same noise-driven temporal fluctuations.
Examples of objects include persons or animals or moving vehicles.
In some embodiments, the optical superimposition of the plurality of noisy light response signals includes: a) first noisy light signal associated with a first target location and a first of the target-location-including optical paths; and ii) a second of the noisy light response signals associated with a second target location and a second of the target-location-including optical paths, the second target location being separated from the first target location by at least 1 mm (or at least 0.5 mm or at least 2 mm or at least 5 mm).
In some embodiments, a source of the illumination is aimed from a moving vehicle and/or at a moving vehicle.
It is now disclosed apparatus for optically probing an object(s) and/or a medium and/or an optical path including the object(s) or medium, the apparatus comprising: a) a source of noisy light configured to illuminate the object(s) or the medium to induce, from the object(s) or medium, one or more of noisy light response signals that are randomly or pseudo-randomly modulated; b) an optical detector configured be illuminated by an optical superimposition of at least one of: i) a plurality of the noisy light response signals, each induced noisy light response signal associated with a respective target location of the object(s) or medium and with a different respective target-location-including optical path; and ii) a noisy source light signal of the light source that is to carry out the illumination and to induce the one or more of the noisy light response signals, so as to generate a combination electrical signal describing the optically superimposed plurality of received noisy light response signals; and c) electronic circuitry configured to determine or characterize or detect from the combination electrical signal, at least one of: i) a relationship between power and frequency of the combination electrical signal or a derivative thereof over a discrete or continuous spectrum; ii) a temporal autocorrelation function of the combination electrical signal; iii) a distance parameter(s) involving one or more the objects; iv) a mechanical stress or strain; v) a change in a light propagation time of at least one optical path; vi) a difference in light propagation times of multiple optical paths or a temporal change thereof; vii) mechanical motion of an object; viii) a material or mechanical property of an optical fiber, at least a portion of which is included in the optical path of step (a).
In some embodiments, the electronic circuitry includes any combination of analog electronics, digital electronics and computer code/software.
A 3D digital camera device for acquiring a digital image of a scene comprises: a) a noisy light source configured to generate noisy light that is randomly or pseudo-randomly modulated, thereby illuminating a plurality of different scene locations within the scene to induce noisy light response signals from the different scene locations within the scene; b) an image sensor including a substantially-planar two-dimensional array of photodetector; c) optical components configured to focus or re-direct noisy light received from the scene onto or to the image sensors, the optical component(s) and the image sensor being configured so that each photodetector of the two-dimensional array: i) is respectively illuminated by a different respective optical superimposition noisy light signal that is an optical imposition of: A) a different respective noisy light response signal from a different respective scene location; and B) a respective reference optical signal whose temporal noise fluctuations are correlated to and temporally offset from the respective noisy light response signal; and ii) generates a different respective temporally-fluctuating electrical signal that respectively describes the respective optical imposition noisy light signal; d) electrical circuitry configured to compute from temporal power spectral density data or temporal autocorrelation data of the temporally-fluctuating electrical signals generated by the photodetectors, a three-dimensional digital image including a plurality of pixels corresponding to the locations in the scene, each visually pixel representing depth data and grayscale or color data at respective location.
A 3D digital camera device for acquiring a digital image of a scene comprising: a) a noisy light source configured to generate noisy light that is randomly or pseudo-randomly modulated, thereby illuminating a plurality of different scene locations within the scene to induce noisy light response signals from the different scene locations within the scene; b) an image sensor including a substantially-planar two-dimensional array of photodetector; c) optical components configured to focus or re-direct noisy light received from the scene onto or to the image sensors, the optical component(s) and the image sensor being configured so that each photodetector of the two-dimensional array: i) receives a different respective noisy response signal from a different respective scene location; ii) generates a different respective temporally-fluctuating electrical signal that respectively the respective noisy response signal from the respective scene location; d) electrical circuitry configured to compute from temporal power spectral density data or temporal autocorrelation data of the temporally-fluctuating electrical signals generated by the photodetectors, a three-dimensional digital image including a plurality of pixels corresponding to the locations in the scene, each visually pixel representing depth data and grayscale or color data at respective location.
In some embodiments, the electrical circuitry includes any combination of analog and/or digital electronics and/or software.
In some embodiments, the image sensor and the electrical circuitry are configured to generate 3D video content of the scene.
In some embodiments, the scene is a landscape scene or microscopic scene or a medical scene.
A method of employing a light source and a detector to optically probe an object(s), medium or an optical path with noisy light, the method comprises: a) sending light from the light source to the light detector so that the light travels along an optical path en route from the source to the detector so that at least one noisy light signal from the sent light illuminates the optical detector; and b) for two or more noisy different electrical signals or sub-signals that co-reside within a common combination electrical signal or that reside in separate electrical signals, the electrical signals sharing substantially the same noise-driven temporal fluctuations as the illuminating at least one noisy light signal such that two or more of the noisy electrical signals are temporally-offset from each other, determining or characterizing or detecting from the combination electrical signal, at least one of: i) a relationship between power and frequency of the combination electrical signal or a derivative thereof over a discrete or continuous spectrum; ii) a temporal autocorrelation function of the combination electrical signal; iii) a distance parameter(s) involving one or more the objects; iv) a mechanical stress or strain; v) a change in a light propagation time of at least one optical path; vi) a difference in light propagation times of multiple optical paths or a temporal change thereof; vii) mechanical motion of an object; and viii) a material or mechanical property of an optical fiber, at least a portion of which is included in the optical path of step (a).
Apparatus for optically probe an object(s), medium or an optical path with noisy light, the method comprising: a) a light source configured to send light from the light source to the light detector so that the light travels along an optical path en route from the source to the detector so that at least one noisy light signal from the sent light illuminates the optical detector; b) the optical detector configured to generate a detector electrical signal according to the noisy light signal illumination; c) electronic circuitry configured to process at least two or more noisy different electrical signals or sub-signals that co-reside within a common combination electrical signal or that reside in separate electrical signals, the processed signal(s) derived at least in part from the detector electrical signal, the processed electrical signals sharing substantially the same noise-driven temporal fluctuations as the illuminating at least one noisy light signal such that two or more of the noisy electrical signals are temporally-offset from each other, determining or characterizing or detecting from the combination electrical signal, at least one of: i) a relationship between power and frequency of the combination electrical signal or a derivative thereof over a discrete or continuous spectrum; ii) a temporal autocorrelation function of the combination electrical signal; iii) a distance parameter(s) involving one or more the objects; iv) a mechanical stress or strain; v) a change in a light propagation time of at least one optical path; vi) a difference in light propagation times of multiple optical paths or a temporal change thereof; vii) mechanical motion of an object; and viii) a material or mechanical property of an optical fiber, at least a portion of which is included in the optical path of step (a).
A method of employing a light source and a detector to optically probe an object(s), medium or an optical path with noisy light, the method comprising: a) sending light from the light source to the light detector so that the light travels along an optical path en route from the source to the detector so that at least one noisy light signal from the sent light illuminates the optical detector; and b) processing the electrical signal generated by the optical detector so as to determine or characterize or detect at least one of: i) a distance parameter(s) involving one or more the objects; ii) a mechanical stress or strain or indication thereof; iii) a change in a light propagation time of at least one optical path; iv) a difference in light propagation times of multiple optical paths or a temporal change thereof; vii) mechanical motion of an object; and viii) a material or mechanical property of an optical fiber, at least a portion of which is included in the optical path of step (a).
Apparatus for optically probing an object(s), medium or an optical path with noisy light, the apparatus comprises; a) an optical detector; b) a light source configured to sent light from the light source to the light detector so that the light travels along an optical path en route from the source to the detector so that at least one noisy light signal from the sent light illuminates the optical detector and to cause the optical detector to generate an electrical signal describing illuminating noisy light signal(s); c) electronic circuitry configured to process the electrical signal generated by the optical detector so as to determine or characterize or detect at least one of: i) a distance parameter(s) involving one or more the objects; ii) a mechanical stress or strain or indication thereof; iii) a change in a light propagation time of at least one optical path; iv) a difference in light propagation times of multiple optical paths or a temporal change thereof; vii) mechanical motion of an object; and viii) a material or mechanical property of an optical fiber, at least a portion of which is included in the optical path of step (a).
The claims below will be better understood by referring to the present detailed description of example embodiments with reference to the figures. The description, embodiments and figures are not to be taken as limiting the scope of the claims. It should be understood that not every feature of the presently disclosed portable media device and method of operating the same is necessary in every implementation. It should also be understood that throughout this disclosure, where a process or method is shown or described, the steps of the method may be performed in any order or simultaneously, unless it is clear from the context that one step depends on another being performed first. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning “having the potential to’), rather than the mandatory sense (i.e. meaning “must”).
Embodiments of the disclosed subject matter relate to optical-noise-radar-based apparatus and methods for optically probing an object and/or a medium using ‘noisy’ optical radiation. It is well-known in the art that optical radiation is subdivided into ultraviolet radiation (UV), the spectrum of light visible for man (VIS) and infrared radiation (IR). In the present disclosure, the terms ‘light’ and ‘optical radiation’ are used interchangeably—noisy light can refer to any combination of UV, VIS and/or IR light.
The term ‘noisy’ light refers to light that is randomly or pseudo-randomly modulated—the modulation may be any combination of: 1) amplitude modulation, 2) phase modulation, 3) frequency modulation, and/or 4) polarization modulation.
In some embodiments, the cross-correlation between a noisy return optical radiation signal of returning from a target and a noisy source light signal used to illuminate the target peaks at a time delay corresponding to the round-trip time to the target. Knowledge of this temporal cross-correlation is thus useful for computing distance-related parameters and other parameters described below.
Some embodiments of the disclosed subject-matter relate to the following features:
(i) An apparatus and method for probing an object, medium and/or light path(s) where a superimposition of two or more noisy light signals is received into the same optical detector (FEATURE A). This optical detector is thus simultaneously illuminated by the superimposed noisy light signals. Even though these noisy light signals are only detected when superimposed on each other, it is possible to compute physical parameters related to the fact that these two or more noisy light signals are distinct from each other. In some embodiments, an indication of a temporal relationship between these two or more noisy light signals that is contingent upon these signals having substantially identical noise content is used to derive one or more physical parameters of the object, medium or an optical path(s) involving the object. (see, for example,
(ii) three-dimensional cameras based upon optical noise radar—for example, as ‘stand-alone’ products or as part of a computer gaming system or in any other context—see, for example,
(iii) optical noise-radar based systems and methods whereby the target object or medium itself imbues light with ‘noise’ characteristics—see, for example,
(iv) optical noise-radar based systems and methods for measuring an impulse response of a target option of medium—see, for example,
(v) optical noise-radar-based systems for measuring and/or monitoring a mechanical and/or material property of an optical fiber—see, for example, FIGS. 9 and 15-17 (FEATURE E);
(vi) optical noise-radar-based intrusion detection systems and methods—see, for example,
(vii) optical noise-radar-based systems for measuring a temporal change in an optical path (FEATURE G)—an optical path is not necessarily the same as a physical path, and may change when a physical path length changes or when an optical property of a object or medium along the path changes—for example a refractive index or a reflectivity or any other optical property;
(viii) optical noise-radar-based systems where noisy light received from a target is processed according to a spectral technique where only specific discrete frequencies are monitored and/or optical power properties are detected only for specific discrete frequencies (FEATURE H)—this is in contrast to spectral techniques where a continuous spectrum is monitored.
Various embodiments may include any feature disclosed in the present document, including but not limited to the aforementioned features or any other feature(s), in any combination including combinations explicitly described in the present disclosure, and other combinations not explicitly mentioned herein (for example, for the sake of brevity).
In some embodiments, it is possible to measure and/or detect and/or monitor any of the following by according to temporal patterns in noisy light received from a target:
(i) a distance (or velocity) to an object(s) or between object(s);
(ii) an object shape, or dimensions of an object;
(iii) relative distances between (and hence, any geometric feature of) multiple targets—e.g. multiple objects or multiple locations on a single object and/or multiple locations within a medium;
(iv) an impulse response of light;
(v) a change in one or more optical paths traversed by noisy light;
(vi) a velocity and/or Doppler-related parameter.
In some embodiments, it is possible to process a noisy light signal received into an optical detector(s) using any combination of the following signal-processing techniques:
(i) spectral techniques see, for example,
(ii) temporal or correlation techniques—the noisy light is detected by an optical detector to generated an temporally-varying electrical descriptive thereof. This electrical signal is processed using an electrical delay line or using computer memory to explicitly determine a correlation according to some time delay between the detected noisy light with the original noisy light.
Steps S505 of
Although certain embodiments may be explained in the present document in terms of one or the other of the above signal-processing techniques (or any other technique), there is no requirement (unless stated otherwise) that any given system or method is limited to any specific signal-processing technique.
In
In the example
Surprisingly, it is possible to measure the optical impulse response without requiring the generation of a very short pulse. In contrast with optical time-domain reflectometer (OTDR) technique which rely on very short pulses to measure an impulse response and to measure mechanical and/or material properties of the optical fiber, in some presently disclosed embodiments it is possible to measure an impulse response and/or characterize the length and/or attenuation of an optical fiber and/or to characterize split and/or mated-connector losses and/or break or other faults in the fiber and/or distribution of the light among modes of a multi-mode fiber and/or to characterize mechanical properties of an optical fiber without relying on very short pulses.
In some embodiments, it is possible to detect mechanical motion of one or more fiber optic cables by monitoring noisy light signals transmitted within the fiber optic cables. In various non-limiting example use cases, optical noise-radar-based techniques for intrusion detection may be used (i) to monitor, in ‘real time’ if a person climbs a fence and moves or otherwise stresses or strains a fiber optical cable attached to the fence and/or to measure a location where the fence is climbed; (ii) if someone sabotages or attempts to sabotage an fluid pipeline (e.g. a pipeline for transporting fuels such as oil or other petroleum products) where a fiber optic cable is mechanically coupled to the pipeline and runs along the length of the pipeline; and/or (iii) to detect sabotage or attempted sabotage of a fiber optical communications cable.
The previous paragraph presented certain fiber-optic-cable related examples related to intrusion detection. This is not a limitation, and in other examples, it is possible to detect intrusion detection in other situations where fiber optic cables are not required.
For many applications, in order to determine a distance-related parameter and/or an impulse response and/or a frequency response and/or an intrusion-related event it is necessary to monitor properties of noisy light received into an optical detector over a continuous spectrum of frequencies. For example, according to the double spectrum technique, after computing an amplitude and/or phase spectrum ] of a temporal electrical signal generated by the optical detector and descriptive of a light signal received including light from the target(s), it is useful to compute an inverse FFT (fast Fourier transformation) of a broad-band spectrum of frequencies in order to measure temporal delays between two different noisy light signals. For example, this technique may be used to measure a temporal relationship between a ‘source light signal’ used to illuminate the target and a return noisy light signal from the target.
Instead of measuring a power amplitude and/or phase spectrum for a continuous range of frequencies (e.g. for the purpose of the ‘double spectrum technique’), according to the routine of
In the example of
In the example of
In the example of
Teaching(s) of
In the system of
It is possible to monitor, over time, an autocorrelation of the light signal with a particular delay time. When the upper and lower fibers are simultaneously mechanically disturbed, temporal autocorrelations of the noisy optical signal in both the upper and lower fiber will change—however, they will not necessarily change at the same time. In the event that delta is much closer to Z=0, the temporal autocorrelation in the lower fiber will change at an earlier time than the temporal autocorrelation in the upper fiber. It is possible to measure a location z=delta in accordance with a positive or negative ‘time gap’ between (i) a first time when a temporal autocorrelation of a noisy light signal in the upper fiber changes; and ii) a second time when a temporal autocorrelation of a noisy light signal in the upper fiber changes.
In some embodiments,
A Discussion of
Applications of the technique of
In step S1101, a) light (i.e. optical radiation—this may be UV, visible, or any IR such as NIR, thermal IR or far IR) is sent from the light source to the light detector so that the light travels along an optical path en route from the source to the detector so that at least one noisy light signal from the sent light illuminates the optical detector.
The optical path may include and/or contact and/or traverse a target location so that the light is reflected and/or transmitted and/or deflected and/or otherwise modulated at the target location. In some embodiments, the light is noisy before reaching the target location. Alternatively or additionally, the light is imbued with noisy characteristics at the target location.
In different embodiments, there may be one or more than one detector and/or one or more than one target and/or one or more than one optical path.
For example, in
As seen in
The noisy signal(s) of S1101 are detected (NOT SHOWN IN
In step a signal processing operation S1105 and/or an optical-path-related detection operation S1109 is carried out for one or more of: (i) a combination electrical signal in which both sub-signals co-reside and/or (ii) a non-trivial mathematical function of (e.g. sum of, difference of, product of or any other non-trivial mathematical function) of the signals or sub-signals.
In one example, the ‘input’ steps step S1105 and S1109 is the single signal from a detector illuminated simultaneously by the two different noisy light signals as a superimposing. In another example, one of the (sub)signals comes from the noise circuitry 90 without any need for optical diction for the (sub)signal.
In another example (see, for example,
Signal-processing operations in step S1105 may include characterizing any combination of:
(i) a relationship between power and frequency of any non-trivial mathematical function of the electrical signals or sub-signals over a discrete or continuous spectrum (see, for example, step S109 of
ii) a temporal correlation function of the electrical signals or a temporal autocorrelation function of the combination electrical signal including the co-residing noisy sub-signals.
Detection operation(s) of step S1109 may include any combination of detecting:
In some embodiments, steps S1105 and/or S1109 may contingent upon the different electrical signals or sub-signals sharing substantially the same noise-driven temporal fluctuations (e.g. according to some signal-processing routine for electrical signal(s) or sub-signals)).
In some embodiments, any one of S1105 and/or S1109 may be carried out in accordance with a speed of light (e.g. in a particular medium)—i.e. in accordance with a relationship between a time delay (i.e. throughout the specification the time delay may be positive or negative and may refer to ‘true delay’ or ‘advance in time) and the speed of light—e.g. to determine a distance parameter.
Embodiments relate to noisy light received from any target and/or noisy light which traverses any medium(s). Teachings disclosed herein may be applied to any object or medium, including but not limited to (i) An optical fiber; (ii) the body of a live animal (e.g. a mammal such as a human) or any portion thereof; (iii) Any type of biological medium; or (iv) Any object or medium that is at least partially obstructed by another object or medium.
For convenience, in the context of the description herein, various terms are presented here. The current section is not intended as comprehensive and certain terms are discussed and/or defined elsewhere in the current disclosure. To the extent that definitions are provided, explicitly or implicitly, here or elsewhere in this application, such definitions are understood to be consistent with the usage of the defined terms by those of skill in the pertinent art(s). Furthermore, such definitions are to be construed in the broadest possible sense consistent with such usage.
For the present disclosure, the term ‘target’ means an object or location to which like is sent from a light source and/or from which noisy light returns in order to illuminate an optical detector.
The terms ‘electrical’ or ‘electronic’ circuitry may be used interchangeably is intended to broadly include any combination of analog or digital circuitry as well as computer-readable readable-code or software.
Electronic circuitry may include may include any executable code module (i.e. stored on a computer-readable medium) and/or firmware and/or hardware element(s) including but not limited to field programmable logic array (FPLA) element(s), hard-wired logic element(s), field programmable gate array (FPGA) element(s), and application-specific integrated circuit (ASIC) element(s). Any instruction set architecture may be used including but not limited to reduced instruction set computer (RISC) architecture and/or complex instruction set computer (CISC) architecture. Electronic circuitry may be located in a single location or distributed among a plurality of locations where various circuitry elements may be in wired or wireless electronic communication with each other.
‘Electrically’ or ‘electronically’ carrying out any process or operation(s) can be accomplished using any combination of analog and/or digital circuitry and/or computer code and/or software.
In the present disclosure, the terms ‘light’ and ‘optical radiation’ are used interchangeably.
Embodiments of the present invention relate to ‘optical radiation.’ It is well-known in the art that optical radiation is “subdivided into ultraviolet radiation (UV), the spectrum of light visible for man (VIS) and infrared radiation (IR).” (website of The Federal Office for Radiation Protection, Germany). It is well-known in the art that infrared radiation may be subdivided into near IR, thermal IR and far IR (see Wikipedia, article on ‘Radiation’). It is well-known in the art that the following types of electromagnetic (EM) radiation are not considered optical radiation: ionizing radiation like x-rays or gamma rays and electromagnetic fields such as microwaves and radio frequencies.
In various embodiments, the ‘EM carrier wave frequency’ of the optical radiation exceeds at least 1012 HZ or at least 5*1012 HZ or at least 1013 HZ or at least 1014 HZ.
The ‘EM carrier wave frequency’ determines the part of the electromagnetic spectrum specific radiation belongs to. Thus, the ‘EM carrier wave frequency’ of UV light exceeds the ‘EM carrier wave frequency’ frequency of visible light.
The ‘EM carrier wave frequency’ should not be confused with the ‘representative noise modulation frequency’ that is representative of the ‘noise modulation frequency range’ or the ‘bandwidth of the noise modulation.’—The ‘noise modulation frequency range’ is the range of frequencies provided by the noise source, and the representative frequency is a representative central tendency value (e.g. a mean). Similarly, the term ‘noise spectrum’ should not be confused with the ‘EM spectrum’—the ‘noise spectrum’ refers to the variety of modulation frequencies at which noisy optical radiation/light is modulated.
In different embodiments, the bandwidth of noise is: (i) at least 107 HZ and/or at least 108 HZ and/or at least 109 HZ and/or at least 1010 HZ and/or at least 1011 HZ; and/or (ii) at most 1013 HZ and/or at most 1012 HZ and/or at most 1011 HZ and/or at most 1010 HZ. Thus, in different embodiments, the ‘characteristic time of the noise’ (i.e. associated with a representative central tendency value (e.g. a mean) of frequencies provided by the noise) is at most 10−7 seconds and/or at most 10−8 seconds and/or at most 10−9 seconds and/or most 10−10 seconds and/or at most 10−11 seconds and/or at least 10−12 seconds and/or at least 10−11 seconds and/or at least 10−10 seconds and/or least 10−9 seconds and/or at least 10−8 seconds.
When the term ‘frequency’ or ‘spectrum’ or ‘frequency spectrum’ appears without any modification, the skilled artisan should understand whether it the EM carrier wave (i.e. which is UV, or visible or IR) or to the noise source. In case of doubt, it should be assumed that the term ‘frequency’ or ‘spectrum’ or ‘frequency spectrum’ refers to the noise source and/or type of modulation provided in the context of ‘noisy light.’
When light/optical radiation is detected by an optical detector, the optical detector generates an electrical signal whose temporal variations describe temporal variations of the power of the optical radiation illuminating the detector. It is possible to analyze this electrical signal to determine an a power spectrum, amplitude spectrum (the square-root of the power spectrum) and a phase spectrum associated with the frequency spectrum of the electrical signal.
Some embodiments relate to a ‘slow’ optical detector. A ‘slow’ optical detector has a response time (for example, between 10−11 seconds and 10−9 seconds) that is much slower (for example, by a factor of at least 10, or a factor of at least 50, or a factor of at least 100, or a factor of at least 500, or a factor of at least 1,000) than a time scale of a carrier frequency of the ‘high’ frequency noise light (for example, less than 10−12 seconds). The term ‘slow’ is not an absolute term but rather a relative to a characteristic time of a carrier wavelength of specific optical radiation used. For some wavelengths, all optical detectors are, in fact, slow, and there is no technology available today where the optical detectors are fast enough to not be considered ‘slow.’ One salient feature of these slow optical detectors is that they can only measure an average power of light received into the optical detector over a time scale that is much slower than a time scale of the electromagnetic carrier frequency of the optical radiation (i.e. UV or visible or IR light).
Without limiting what is written above, in some embodiments, the optical detector is slower or much slower (for example, by a factor of at least 10, or a factor of at least 50, or a factor of at least 100, or a factor of at least 500, or a factor of at least 1,000) than a ‘characteristic time of the noise’
In some embodiment, the time scale of the optical detector and/or the electronics is greater than a time scale of the noise. This would mean that the optical detector is slower than the noise and/or when analyzing an electrical signal(s) including noise fluctuations, it may be useful to average the electrical signal(s) over a sliding window whose width is at least some fraction of a time scale of the noise (i.e. at least 0.1 times or at least 0.5 times or at least 1 times or at least 1.5 times or at least 2 times or any other value that the skilled artisan would conclude to be useful after reading the present disclosure).
When one or more characteristic(s) of light is modulated randomly and/or pseudo-randomly, this produces ‘noisy light.’ The ‘noise’ can be introduced to the light before the light reaches a ‘target’ or at a location of the ‘target.’ Light characteristics that can by modulated randomly and/or pseudo-randomly include any combination of amplitude and/or phase and/or frequency and/or polarization. Techniques for generating noisy light are discussed below—for example, with reference to
The noise-spectral characteristics of ‘noisy light’ are such that the average of the squared amplitude of the frequency spectrum PSDin≡|Sin(f)|2, where PSD stands for power spectral density and Sin(f) is the Fourier transform of sin(t) is preferably substantially constant over a frequency range from f=0 to f=Δf, where sin(f) is the optical power of the optical noise source.
Thus, a ‘flat frequency distribution’ associated with white noise is not required. In some embodiments, this is preferred. In other embodiments, the ‘flat frequency distribution’ may not be present—however, it may be possible to correct for this, for example, if the frequency distribution is known a-priori.
A ‘distance’ parameter refers to the physical distance between two points in any context—for example, a distance between a light source (or detector or any other point outside of an object) and an object(s), a distance between two or more objects, and distance(s) between two or more points on an object. Thus, distance refers to absolute distance and relative distances or any combination thereof. According to this logic, the shape and the size of objects are also considered ‘distance parameters’ since they are characterized by distances between locations on the object. Another example of a ‘distance parameter’ is a surface roughness or surface topography.
A ‘time derivative of a distance parameter’ may refer to an absolute velocity, acceleration or any other non-trivial combination involving any time derivative of the distance parameter. Because the distance parameter defined generally in the previous paragraph, the ‘time derivative’ may refer to translational time derivatives, rotational time derivative, deformational time derivative or any other derivative describing motion of the object(s).
When a target is illuminated with light, the illuminated target generates a light response signal which is sometimes referred to as ‘returning’ from the target. A target ‘responding’ to light refers to any combination of reflection and/or deflection and/or scattering and/or transmission. The term ‘transmission’ in the context of a ‘target’ refers to light being modulated by the target but does not require that light is emitted from the target—i.e. it is understood in the context The term ‘return’ only refers to the light moving away from the target, and does not restrict in any manner any light direction or any relationship between (i) a direction of light before interacting with the target and (ii) a direction of ‘returning from’ the target.
Furthermore, it should be understood that there is no implication in use of the term ‘return’ (or in any other context in the specification) that the light source and the light detector are required to be at the same location (or ‘near’ to each other). Although this configuration is observed in a number of embodiments, this is not at all a requirement, and in some embodiments, the source and the detector and/or more than one source or more than detector can be ‘far’ from each other.
In some embodiments, a ‘target’ is a distinct object. This is not a limitation. In some embodiments, a target may be a region within an object and two targets may actually be within the same object (for example,
An ‘optical path length’ relates to the physical path length and the refractive index of locations through which the optical path traverses. Two optical paths may have distinct lengths because their physical lengths are different or because refractive indexes at any location(s) along the optical paths are different.
When there are two more different or distinct targets, they are separated from each other by some sort of distance. In some embodiments, the ‘minimum separation distance’ for two targets to be considered distinct from each other is at least 0.5 mm or at least 1 mm or at least 2 mm or at least 5 mm or at least 1 cm or at least 5 cm or at least 10 cm. This distance can be a fixed distance or can fluctuate in time. When it fluctuates in time, the distance between the two targets refers to a time when light is incident on both targets to produce a noisy light response signal. In some embodiments, light incident upon each target may be associated with a different optical path. For example, in
For two optical paths to be ‘distinct’ or ‘different,’ they can be either ‘physically distinct’ or ‘optically distinct.’ If the two paths are ‘physically distinct,’ a first optical path must include a segment not included the second optical path, where the length of the ‘not included’ segment is at least 0.5 mm. In different embodiments, the length of the ‘not included’ segment is at least 1 mm or at least 2 mm or at least 5 mm or at least 1 cm or at least 5 cm or at least 10 cm. If the two optical paths are ‘optically distinct’ they do not necessarily have to be physically distinct as defined above—for example, the refractive index at one or more locations along the path may be different.
A Discussion of Non-Limiting Examples of Noisy Light
In an embodiment of the invention, the optical EM radiation field has amplitude Ein(t) that varies in time in a random or pseudorandom fashion and has a power sin(t)=|Ein(t)|2 that is averaged over the averaging time of the measuring detector and associated electronics. This type of radiation naturally exists, for example, in sources of spontaneous emission as discussed in patent U.S. Pat. No. 5,034,678 (incorporated herein by reference in its entirety), which describes luminescent fiber amplifiers and semiconductor optical amplifiers.
However, this type of radiation also includes other sources of optical “noise” radiation that have not been considered in the past, such as: spontaneous scattering and stimulated scattering e.g., Brillouin scattering and Raman scattering; parametric processes such as sum frequency generation, difference frequency generation, second harmonic generation, and all other types of parametric frequency mixing; and radiation from all types of optical media that are in an excited electronic state. This type of optical radiation can also be generated by modulating the light with a modulator that is driven by a random or pseudo-random electronic signal. The spectral characteristics of this signal are such that the average of the squared amplitude of the frequency spectrum PSDin≡|Sin(f)|2, where PSD stands for power spectral density and Sin(f) is the Fourier transform of sin(t), the power signal of the optical noise source, is substantially constant over a frequency range from f=0 to f=Δf.
As stated above, a preferred source of EM radiation is one in which the radiation is varying randomly, either due to a natural process or due to an applied modulation. Several types of sources capable of performing this function are known in the art, and others are disclosed herein. For example a suitable source of EM radiation could be one of the following:
1. Amplified spontaneous emission (ASE) source, such as an erbium-doped fiber amplifier, semiconductor optical amplifier, or another type of medium which is in an excited state due to pumping and is emitting spontaneous or stimulated emission;
2. Spontaneous or stimulated scatter of optical radiation, such as caused by Brillouin scattering or Raman scattering;
3. Luminescence or Fluorescence or other type of EM emission from atoms or molecules;
4. Parametric frequency mixing such as sum-frequency generation, difference frequency generation, second harmonic generation or any other type of EM frequency mixing technique due to a nonlinear mixing effect in a suitable nonlinear medium.
5. Amplitude modulation of any light source with a suitable modulator such that the signal is varying randomly, pseudo-randomly, or varying with some other type of modulation such that the spectrum of the source has relatively constant amplitude over the desired spectral width.
6. A light source displaying chaotic variations in light amplitude, such as laser diodes or other lasers having chaotic temporal statistics.
7. Any light source with temporal modulation such that at least half of its power is situated in a spectral band Δf around f0.
In certain embodiments, the light source is external to the medium to be measured.
In other embodiments, the light source is an integral part of the medium to be studied. For example, an optical fiber will partially scatter injected light in the form of Brillouin scatter and/or Raman scatter, depending upon the optical characteristics of the light source, as is known in the art. These scattering effects cause the light to fluctuate randomly with a characteristic noise bandwidth of approx. 30 MHZ for Brillouin, and significantly broader bandwidth for Raman (typically at least 30 GHZ). In these embodiments, it is possible to utilize the noisy optical radiation to characterize the same optical fiber that is its' source. Applications include: measurement of the fibers' length, strain, stress, temperature, and points of power loss or gain. This description is given as an example only. Any of the previous listed optical noise sources and others known in the art can be utilized to measure certain features of the noise source itself.
It will also be understood that in all of the embodiments, the use of one radiation source is not to be taken as a limitation. All of the embodiments can involve one or more radiation sources, where the noise characteristics of the sources may be fully correlated, partially correlated or have no correlation between them, and where the electromagnetic bandwidth of each of the sources may overlap fully, partially or not at all with each of the other sources.
In some embodiments relate to
A Discussion of
One salient feature of any of the routines of
In one particular example related to
Various embodiments refer to ‘first’ and ‘second’ optical or electrical signals—this is not limiting, and it is appreciated that ‘third’ and/or ‘fourth’ or any number of signals may be provided. A ‘plurality’ refers to two or more even when in the present disclosure only the ‘first’ and ‘second’ signal (or any other item) is explicitly described.
FIGS. 1 and 18-19 are flowcharts of routines for optically probing an object(s) or a material(s). In some embodiments, a function of two ‘noisy’ signals determined—for example, between first and second noisy light signals, or between a first signal that is a noisy light signal and a second signal that is a noisy electrical signal, or between first and second noisy electrical signals. As will be discussed below, in
In every one of these cases, the stochastic or noise of the first and second noisy light signals are substantially correlated with each other—however, there is a time delay (i.e. constant in time or varying in time) between these noisy signals that temporally fluctuate in substantially the same manner but offset by a time delay . As will be discussed below, it is possible to compute (e.g. see step S113 of
As noted above, in order to compute a temporal autocorrelation between two noisy signals, spectral or temporal signal processing techniques may be employed in various embodiments. Step S109 of
Reference is now made to
Passive optical component(s) 106A is configured so that at least some light returning from the target 150 (for example, a majority of the returning light or substantially all of the returning light) is directed to optical detector 120. As such, optical detector4 120 receives a mixture of (i) a ‘first’ noisy light signal of noisy light which has traversed a first optical path whose length is substantially the sum of ‘Optical Path Segment A’ and ‘Optical Path Segment B’—this noisy light is referred to as the ‘reference light signal’ and is substantially equal to the ‘source signal’ and (ii) a ‘second’ noisy light signal of noisy light which has traversed a second optical path that ‘reaches’ the target and also includes optical path segment B.
The stochastic or noise properties of the first and second signals are correlated with each other—however, there is a constant (or varying) time delay between these noise properties. As will be discussed below, it is possible to compute any number of properties from the temporal relation between the first and second light signals—for example, a distance to an object, a shape of an object, a distance between more than one object, a shape of an object, and additional properties discussed elsewhere in this document.
In the example of
Passive optical component(s) 106B is configured so that at least some light returning from the first and second targets is directed to optical detector 120. As such, optical detector 120 receives a mixture of (i) a ‘first’ noisy light signal of noisy light which has traversed a first optical path that contacts the top of the house and includes Path Segment B′ and (ii) a ‘second’ noisy light signal of noisy light which has traversed a first optical path that contacts the top of the house and includes Path Segment B″.
In the example of
In
In
The two electrical signals may be subjected to any signal processing technique including but not limited to temporal techniques and spectral techniques.
A Discussion of
In step S101, a ‘target’ object(s) or medium(s) is illuminated using ‘noisy’ coherent and/or incoherent ‘high frequency’ light which may include any combination of ultraviolet and/or visible and/or near infra-red (NIR) and/or infra-red (IR) and/or far infra-red (FIR) spectra light. In some embodiments, an apparatus including a noisy light source (for example, see 100 of
In yet another example (not shown explicitly in the figures), the illumination is provided by ambient light—for example, sunlight. In this example, it is not necessary for the ‘illumination’ to be carried out by any apparatus—this illumination could be provided by nature.
In some embodiments, the illuminating light travels to or from the target in substantially free space. Alternatively or additionally, at least a portion of the light illuminating light may travel via a medium—for example, an optical waveguide such as an optical fiber.
After the target is illuminated, the target responds by reflecting and/or deflecting and/or scattering the illuminating light and/or modulating the illuminating light as it traverses the target or a portion thereof. The result of the target's response is a ‘returning light signal’ of noisy light which is received into one or more optical detectors in step S105. In
In step S105, returning light signal(s) are received into detector 120. As noted throughout this document, in some examples, the same detector receives more than one light signal, and the more than one returning light signal(s) are received together (see
In other examples there is no need (for example, in step step S105) to superimpose multiple noisy light signals onto the same detector to simultaneously illuminate the same optical detector 120. For example, in
In step S105, the optical detector 120 generates a temporally-fluctuating electrical signal (e.g. analog and/or digital signal) descriptive of the temporal fluctuations in the local light field and/or light power level at the location of the optical detector. Because the local light field and/or local light power level at the location of the optical detector includes the noisy returning light signal, the electrical signal generated by the detector is also ‘noisy.’
In step S109 of
Appropriate apparatus for carrying out step S109 includes but is not limited to an electronic spectrum analyzer, analog and/or electronic circuitry (e.g. an analog and/or digital electronic computer(s)), and/or an electronic correlator circuit(s). In some embodiments, it is possible to employ any combination of FFT techniques, and/or wavelet technique(s) any other technique known in the art.
In step S113, the amplitude and/or phase spectrum determined in step S109 is analyzed. One exemplary implementation of step S113 relates to the so-called ‘double spectrum technique’ known in the art of RF noise radar.
The non-limiting example of
Phase Retrieval Algorithm
In some embodiments, it is possible to employ a so-called phase-retrieval algorithm in step S109 of
Embodiments of the invention comprise applying a phase retrieval algorithm on the amplitude of the PSD spectrum to determine the phase spectrum associated with the PSD spectrum embodiment associated with the object or medium. These embodiments can further comprise determining the full complex optical power frequency response of the object or medium from the amplitude spectrum and the phase spectrum of the power transfer function spectrum in which case the method can further comprise performing an inverse Fourier transform of the full complex optical power frequency response to determine the optical power impulse response of the object or medium.
A Discussion Relating to Some Embodiments Where a Second Spectral Operation of a Double Spectral Technique is Implemented in Step S113 of
In some embodiments related to the ‘double-spectral technique,’ in step S109 the first spectrum is computed, and in step S113, the second spectrum is computed (for example, by an inverse FFT) to compute an autocorrelation function that may peak at a time gap indicative of the travel time between the source and target (or relative distance of two targets). This information, together with speak of light information, may provide distance indications.
Thus, in some embodiments, it is possible to determine the relative distances between the locations on the medium which are the sources of the radiation returning to the detector. This can be determined directly by the spectral transfer function, or, for example, by calculating the inverse Fourier transform of PSDmedium which gives a temporal correlation signal which peaks at temporal locations where the returning radiation originates, or by other means, such as that described as follows:
The correlation between the two power signals sin(t) and sout(t) is directly determined in a fashion known in the prior art by mixing the two signals in an appropriate mixing circuit while scanning the time delay τ of the reference signal sin(t−τ) with respect to the optical signal from the target sin(t−T). This gives a peak correlation at times τ=T from which the distance to the target can be determined.
When the characteristics of the optical power frequency response of the object or medium are determined in this manner, the inverse Fourier transform of the amplitude squared of the power transfer function is calculated. From the inverse Fourier transform a temporal correlation between the power signals of the illuminating radiation and the returning radiation is determined and from this correlation one or both of the following are determined: the distance from the measurement system to the locations on the object or medium from which the radiation returning from the object or medium originates and the relative distance between locations on the object or medium from which the returning radiation originates.
Some embodiments of the present section related to a situation where in step S109 the first spectrum is computed, and in step S113, the second spectrum is computed (for example, by an inverse FFT).
Alternatively or additionally, the spectrum information computed in step S109 may be processed using other signal-processing routines, and there is no need to always effect a double spectrum technique.
A Mathematical Discussion Relating to ‘Feature A’—for example, as implemented in any of
In all of
It is shown in these embodiments described above and further described below. that despite the fact that the signal is optical and the detector is ‘slow” relative to the EM field fluctuations, it is possible to measure important spectral and temporal characteristics of the medium's response to optical power signals, as well as its' distance to the measurement system and the locations of multiple reflections in the target medium, by analyzing the power signals associated with the noisy EM field with no requirement to analyzed the EM fields.
Not wishing to be bound by any theory, in this section, a mathematical discussion of scattering of “noisy” EM, its detection by a “slow” detector, and the conclusions regarding analysis of this system using well-known linear system characterization methods are presented.
Given two EM field Ein,1(t) and Ein,2(t) having power signals sin,1(t)=|Ein,1(t)|2 and sin,2(t)=|Ein,2(t)|2 respectively.
Suppose the medium consists of multiple scatterers and is illuminated with Ein,1(t). In this case, the output EM field is composed of the sum of the scattered fields from each scatterer:
where Tn are time delays caused by the scatterers and an are the corresponding coefficients.
The corresponding output power is then
However, if the medium varies in time, and/or if the EM field varies randomly in time, so that the interference term (the right-hand term) is zero after a suitable averaging time, then
As a consequence the medium acts as a linear system for the average power. This can be seen as follows by checking that superposition holds in this system:
If the medium is illuminated with two fields such that
s
in(t)=A
sin,1(t)
+B
sin,2(t)
which agrees with the superposition criterion. In addition, if the medium is time-invariant, then it can be characterized by the well-known principle of linear time-invariant (LTI) systems:
s
out(t)=hp(t)*
sin(t)
S
out(f)=Hp(f)·Sin(f)
where hp(t) is the power impulse response for the medium, Hp(f) is its' Fourier transform, Sout(f) is the spectrum of sout(t), and all the conclusions related to LTI systems can be applied here including the use of Fourier transforms and inverse-Fourier transforms which connects between the temporal power response and the spectrum of the power signal, as well as the use of the Kramers Kronig or other phase-retrieval analyses to determine the phase spectrum associated with Hp(f).
The spectral response of the specific embodiment that is shown in
Reference is made to
E
out(t)=p1Ein(t)+p2Ein(t−T),
where T=2δL/c is the relative time-lag for the arrival at beam splitter 1 of the beam reflected from g2 with respect to that arriving from g1 due to a difference in propagation distance δL to the two elements, and p1 and p2 are the effective transmission coefficients of the beams through the system.
For the reasons discussed above, if the radiation is varying randomly in time, then the output power will be the sum
s
out(t)=|ρ|2(sin(t)+sin(t−T)),
where for simplicity it is assumed that |p1|2=|p2|2=|ρ|2. This is the power that is measured with a detector having a suitable electronic bandwidth, where due to the time-response of the detector, it performs an averaging as well, so that the above represents the power after the averaging.
The Fourier transform of this signal is:
S
out(f)=|ρ|2Sin(f)(1+e−2πfT).
Therefore in this case PSDout for the sum of the two signals is:
PSD
out,sum
≡|S
out(f)2=2|ρ|2|Sin(f)|2[1+cos(2πfT)], equation [1]
such as is measured with an electronic spectrum analyzer.
Note that the spectrum is sinusoidal, with a period that is dependent upon the distance between the two reflectors due to the time delay T. In order to acquire at least one cycle of this spectrum, it is necessary to measure the signal with an electronic bandwidth of approximately Δf=1/T=c/2δL. For example, for δL=10 cm, a bandwidth of 1.5 GHz is needed to acquire one full cycle of the spectrum This information can then be used to determine the distance to the target, since the distance to the reference reflector g1 is known. This model only treats the case of one reflection location on the target; however it can be extended to the case of more than one location, so that these locations can be determined as well.
In many situations it is sufficient to acquire the spectrum over a portion of the bandwidth Δf. This will reduce the electronic and detector bandwidth requirements accordingly, and will allow for increasing the detectors' active area, so that it will be more sensitive. For example, if the number of reflections from the target is known a priori, then it is possible through appropriate signal analysis, estimation and extrapolation techniques to measure the PSDout,sum over a bandwidth that is smaller than Δf and still acquire knowledge of distance with a depth resolution δL that approx. corresponds to Δf
Therefore, in a variation of the embodiments described herein above, only a portion of the spectrum is measured by utilizing a bandwidth less than Δf. For example, in the case of one reflection from the target, only a portion of the sinusoidal cycle is measured, and the cycle period is determined through known signal estimation techniques and other signal analysis techniques. The ability to utilize a bandwidth less than Δf is advantageous since it relaxes the speed requirements on the detectors and other electronic components of the system.
It is pointed out that the power signal PSDout,sum can also be obtained using other configurations—for example, see
In another variation of embodiment using only one detector, a further inverse-Fourier transform is performed on PSDout,sum described in equation 1 to determine the correlation between the power signals returning from the target and that of the irradiation, which shows a characteristic peak at the time delay T, from which the distance to the target can be determined. As explained above, if more than one source of returning radiation exists on the target, their locations can be identified as well with this technique.
A Further Discussion of
In the example of
Thus, some embodiments relate to apparatus for acquiring a digital image of a scene comprising: a) a noisy light source 100 (not shown in
In general, there is no requirement to include the ‘technology’ of
Thus, in some embodiments, each photodetector 120 of the two-dimensional array 170: i) is respectively illuminated by a different respective optical superimposition noisy light signal that is an optical imposition of: A) a different respective noisy light response signal from a different respective scene location; and B) a respective reference optical signal whose temporal noise fluctuations are correlated to and temporally offset from the respective noisy light response signal. In these embodiments, each photodetector thus) generates a different respective temporally-fluctuating electrical signal that respectively describes the respective optical imposition noisy light signal.
Not wishing to be bound by any theory, it is noted that the cost-savings (i.e. in terms of computational power required) for embodiments where there are a plurality of photodetectors, for example, a large (e.g. at least 50 or at least 100 or at least 200 or at least 500 or at least 1,000 or at least 5,000) number of photodetectors of a two-dimensional array for image sensing may be substantial.
In some embodiments, a reference noise light signal is provided to each photodetector—for example, it is possible to simultaneously illuminate each photodetector of the array with the same ‘noisy light source signal’ that acts as a reference. In this case, each photodetector is simultaneously illuminated by: (i) a common source noisy light signal that is common to two or more of the photodetectors and (ii) respective target/scene-specific noisy light signal that is particular for a location in the scene for that photodetector (i.e. which will be represented as a pixel). Nevertheless, the use of a ‘common reference noisy light signal’ is not a limitation, and in other embodiments, it is possible to simultaneously illuminate photodetectors 120 of an array 170 by multiple noisy light signals without employing common references.
As with any embodiment, the ‘noisy light’ may be UV light and/or visible light and/or IR light (e.g. near IR light or thermal IR light or far IR light).
The source of the noisy light may be provided in any location—for example, mechanically coupled to the photodetectors via some sort of common device housing or in any other location (coupled or not).
A Discussion of Noisy Light with Reference to
In various embodiments, a noisy light signal from a target object(s) or medium(s) is received into one or more optical receivers.
In different embodiments, one or more of (i.e. any combination of) 1) amplitude modulation, 2) phase modulation, 3) frequency modulation, 4) polarization modulation may be used to produce ‘noisy light.’
In particular, examples of possible amplitude modulation are 1) pulsed, 2) sinusoidal, 3) amplitude modulation such that the autocorrelation of the power signal has a Gaussian dependence on time, 4) amplitude modulation such that the autocorrelation of the power signal has a super-Gaussian dependence on time.
As noted earlier, in embodiments related to
Thus, in some embodiments, it is possible to provide apparatus that imbues noise characteristics upon at least one of the following: 1) the radiation source; or 2) the radiation in at least one of the optical paths between the illuminating radiation and at least one of the detectors.
In
As noted above, in order to produce ‘noisy’ light, it is possible to randomly or —pseudo-randomly modulate any combination of: light amplitude, light phase, light frequency and light polarization. Furthermore, in some embodiments, the modulation (e.g. amplitude modulation) may be 1) pulsed, 2) sinusoidal, 3) amplitude modulation such that the autocorrelation of the power signal has a Gaussian dependence on time, 4) amplitude modulation such that the autocorrelation of the power signal has a super-Gaussian dependence on time.
A Discussion of Computing a Phase Spectrum and of Computing Impulse Response with Reference to Step S109 of
In addition to the above embodiments and applications, there will now be described embodiments for acquiring the optical impulse response of EM media. For example, a well-known technique known as pulsed laser radar for measuring the distance to the front of a remote object is to transmit a short pulse, on the order of nanoseconds, and measure the time it takes for the pulse to return to the detector. This technique is limited in depth resolution by the pulse length. This can be improved in principle by shortening the pulse width to have duration less than nanoseconds, but this comes at a significant cost in complexity and price. Moreover, this time-domain technique requires complex synchronization electronics. The invention disclosed herein overcomes these limitations by achieving high depth resolution without requiring short pulses.
In the embodiments described above, the true impulse response of the EM media (or “target”) to a pulse of EM power is not determined; rather, the temporal correlation function of the power signal returning from the media is determined. This is usually sufficient for media for which a small number of discrete scattering or reflection events take place.
If the target is more complex, e.g. consists of a large number of discrete scattering events, or continuously scatters the light in a diffuse fashion, then the PSD spectrum will accordingly be more complex as well. Examples of media of this type are: clouds, smoke, biological tissue, clothing, camouflage material, the atmosphere under certain conditions, optical fiber, bodies of water and other solids, liquids and gases under certain conditions. Under these conditions, a true impulse response is desired, since a correlation-type of response suffers from reduced temporal resolution and accuracy as opposed to the true impulse response, and so will not be able to temporally resolve the scattering behavior sufficiently. Even if the medium is not complex in terms of the number and type of scattering points, it would still be beneficial to know the true power impulse response, as opposed to the correlation-type of response.
An embodiment of the invention for determining the true power-impulse response of the EM medium is to carry out the following steps:
1. Determine PSDmedium as described in the first embodiment.
2. Calculate √{square root over (PSDmedium)} which is the amplitude spectrum associated with the power transfer function spectrum for the medium.
3. Calculate the phase spectrum θ(f) associated with the said transfer function spectrum of the medium, through a phase-retrieval algorithm such the Kramers-Kronig technique, MEM technique or other techniques as described in, for example, co-pending International Patent Application WO 2009/098694 and U.S. Pat. No. 7,505,135 by the same applicant, the description of which, including publications referenced therein, is incorporated herein by reference; and
4. Calculate the true power impulse response of the medium by calculating the inverse Fourier transform of √{square root over (PSDmedium(f))} exp(iθ(f)).
This impulse response will reveal the relative distance to the various reflection or scattering points in the medium, as well as the overall scattering characteristics of the medium, such as the scattering coefficients, with a temporal resolution and accuracy significantly better than that of the power correlation signal technique.
In a similar fashion, the technique described in the steps above can be used for determining the distance to the target as well as the relative distances between scattering points in the target, by carrying out these 4 steps for the PSDout,sum function as defined in eq. 1.
In step S211, light is sent through an optical fiber. In one example, the noisy light is sent through the optical fiber. In another example, non-noisy light is sent through the optical fiber, but it is possible to employ a Brillouin scattering technique to imbue light with noise characteristics at any location.
In step S215, one or more detectors or illuminated by noisy light (e.g. by one or more noisy light signals—e.g. with or without light superimposition).
In step S219, it is possible to characterize mechanical and/or material properties of the fiber according to a temporally-fluctuating noisy electrical signal whose noise properties substantially correspond to the noise properties of one or more noisy light signals in step S215.
Mechanical or material properties in
In some embodiments, it is possible to measure the static or dynamic light distribution among modes of a multi-mode fiber.
In this figure numeral 9 represents an optical circulator, numeral 10 an optical fiber, and numeral 11 breaks, faults or other sources of power loss in the fiber. This embodiment of the invention can carry out all of the functions of a well-known device known as an optical time-domain reflectometer (OTDR), which measures points of optical loss along the fiber by sending pulsed light and measuring the pulse response reflected from the fiber.
In contrast to OTDR-related techniques, pulsed light is not required . In OTDR techniques, pulsed light may be used to shorten the “dead-zone”, i.e. the depth resolution, associated with the fiber measurement, which is proportional to the pulse length. In order to shorten the dead-zone in an OTDR device, the pulse length must be shortened. This adds complexity and cost to the system.
In some embodiments, the techniques for detecting mechanical and/or material properties of optical fibers do not require upon pulsed radiation—in these embodiments, it may be significantly easier to shorten the dead-zone, by measuring the spectrum over a wider spectral range. The ability to shorten the “dead zone” without requiring a light source with shorter pulses is a basic advantage of the disclosed technique over all other types of pulsed radar systems.
In yet another example, the ability to monitor the reflections from various points along an optical fiber is utilized to form the basis of a sensor of stress or strain on the fiber. For example, assume that the fiber has a series of N reflection points 1, 2, . . . , i, j, . . . N along its length that reflect a small portion of the radiation. These reflection points can be created, for example, with the use of connectors that physically bring the two fiber ends into a touching contact, and/or through the use of fiber Bragg gratings, which reflect a portion of the radiation whose spectral frequency and bandwidth match that of the grating's spectral response. If no pressure is on the fiber at any point, then the system of the invention will show pulsed reflections from each of the reflection points. However, if pressure is applied to a point along the fiber, e.g. between two adjacent reflectors i and j, then the system of the invention will detect this as a reduced reflection from the reflection points starting from point j. Those skilled in the art will understand that it is possible to design sensitive means for detecting pressure in this fashion, through various mechanical means of enhancing the optical loss from the fiber as a result of pressure. If fiber Bragg gratings are employed, then if pressure or strain is applied to one or more of the fiber gratings, then the spectral response of the grating changes, thereby changing the amount of reflection from that grating which can be monitored using a system of this invention.
A Discussion of Intrusion Detection
In some embodiments, it is possible to employ noisy light for ‘intrusion detection’—i.e. to detect mechanical motion of a person or animal or moving vehicle (e g manned or unmanned. This may be useful, for example, to determine in someone or something climbs a fence or moves across an area of land or comes into contact with an optical fiber or oil pipeline.
For example, it may be possible to determine when or if an optical path between a plurality of reflectors becomes blocked due to mechanical motion of an object (e.g. person or animal or moving vehicle) that previously was not blocking the path—see
In another example, it may be possible to measure force imposed (e.g. by someone or something climbing a fence) and/or a change in stress or strain—see, for example,
In step S311, a light signal from a source is sent to a detector via an optical path(s) (e.g. via an optical fiber, fiber free space). In the example of
In
In some embodiments, the routine of
In one example, the optical path is modified by changing its length—for example, an object (e.g. person, animal or moving vehicle) that previously to not block a line of site between left and right reflectors of
In another example, the optical path is modified by changing one or more refraction index properties—for example, by mechanically moving a brag gate of
Thus, in step S319, noisy electrical signal(s) having temporal noise characteristics that match one or more noisy light signals are monitored.
In step S315, according to the monitored signal, it is possible to detector intrusion.
A Discussion of
In some embodiments, it is possible in step S109 of
In some embodiments, it is possible to detect a change in one or more optical paths by computing an amplitude and/or spectrum describing light power as a function of frequency for only a set of discrete frequencies—i.e. over only a discrete ‘spectrum ’
In some embodiments, this is useful for intrusion detection and may reduce the amount of electronics employed to detect changes in optical paths and/or intrusion events.
Thus, in some embodiments related to the ‘double spectrum technique,’ after the power signals are acquired for the illuminating radiation and returning radiation, all of the further steps in the analysis of these signals requires measuring the frequency spectrum of the signals over a full or continuous spectral range Δf. The value of the required spectral range is determined from the desired depth resolution δL≈c/2Δf where c is the speed of light. For example, a 1 GHz spectral range will give a resolution of approx. 15 cm.
In embodiments related to
In the non-limiting example of
Although not illustrated in the figures, it is appreciated that the electronic filters may be augmented with and/or replaced by optical filters that allow only monochromatic light to illuminate any optical detector(s).
In
E
out(t)=aEin(t)+bEin(t−T),
where T=2Ln/c is the relative time-lag for the arrival of the beam reflected from b with respect to that arriving from a due to a difference in propagation distance L to the two elements, n being the refractive index of the medium between the reflectors.
Since the radiation is varying randomly in time, the signal after the optical detector will be proportional to
s
out(t)=(a2sin(t)+b2sin(t−T)),
where sj(t)≈|Ej(t)|2 is the intensity (or power) of radiation field j.
The Fourier transform of this signal is:
S
out(f)=Sin(f)(a2+b2e−2πfT).
Therefore the power spectral density PSDout is:
PSD
out
≡|S
out(f)2≈|Sin(f)|2[a4+b4+2a2b2 cos(2πfT)] (X)
Eq. (X) describes the distribution of the power among the frequency components of the spectrum For our example of two reflectors, it is sufficient to monitor the values of a and b in order to know if a disruption occurred between the two reflectors. This will happen, for example, if b is reduced while a stays constant.
Please note: it is not necessary to monitor the complete spectrum in order to determine these two values.
This can be seen by the following:
For example, the values of a and b can be determined as follows: set the value of filter F1 such that it passes the power within a narrow band of frequencies around f1, which satisfies 2πf1T=π/2, or f1=c/8 nL. The value of the output of this filter, A1, will be proportional to a4+b4. Set the value of filter F2 around f2=c/4 nL, and its output value, A2, will be proportional to a4+b4−2a2b2. From these two values, it is possible to continuously monitor the values of a and b.
A Discussion of
Some embodiments relate to spectrally-selective reflectors such as Bragg gratings.
For example, it is possible to employ wavelength multiplexing so that light from a noise source such as an erbium-doped fiber amplifier (EDFA) having a spectral bandwidth of approx. 30 nm in the telecommunication c-band is directed into an optical fiber. Along the fiber are Bragg gratings (BG) BG1 to BGn which selectively reflect light at wavelengths lambda1, lambda2 . . . lambda n. The returning light from each of these BG possesses statistically independent random noise. With the aid of a circulator, this light is directed into a demux which separates the n spectral components, and directs them to n separate detectors. In parallel, a portion of the noise source is shunted to the same demux. Therefore, detector i receives the light returning from BG i at wavelength i, plus light from the noise source itself at the same wavelength i. This is true for each of the channels i from 1 to n. Then the outputs of these detectors are processed in a fashion similar to the previous embodiment in order to monitor disruption in the light path along the fiber.
In
In different embodiments, the system of
In one example (this relates to
The fibers may be single mode or multi-mode fibers.
In the system of
It is possible to monitor, over time, an autocorrelation of the light signal with a particular delay time. When the upper and lower fibers are simultaneously mechanically disturbed, temporal autocorrelations of the noisy optical signal in both the upper and lower fiber will change—however, they will not necessarily change at the same time. In the event that delta is much closer to Z=0, the temporal autocorrelation in the lower fiber will change at an earlier time than the temporal autocorrelation in the upper fiber. It is possible to measure a location z=delta in accordance with a positive or negative ‘time gap’ between (i) a first time when a temporal autocorrelation of a noisy light signal in the upper fiber changes; and ii) a second time when a temporal autocorrelation of a noisy light signal in the upper fiber changes.
A Discussion of
In another embodiment, the sensing fiber is a multimode fiber 620, and for example step-index multimode fiber (and not graded index).
In this example, the output is noisy light—the input may or may not be noisy light. In
for the N modes. Therefore, the correlation of this signal will look something like the black curve in the plot below, where T1 is the propagation time of the lowest order mode.
If the fiber is perturbed, then more light will be channeled into the higher-order modes, resulting in the red curve above. By comparing the two curves, one can determine that the fiber was perturbed.
Now in order to determine where the perturbation is located, one can employ the same counter-propagating idea described above with reference to
The features in the present section may be combined with any embodiments disclosed herein, in any combination.
In some embodiments, it is possible to increase the optical frequency range in the following fashion: The medium is first irradiated with “noisy” EM radiation having a center frequency f0 and bandwidth Δf. Then the signals are analyzed as described in the first embodiment. In the next step, the center frequency is changed to f1=f0+Δf while the noise characteristics are not changed so that the bandwidth Δf remains the same. Then the power signals are again analyzed as above. This process is repeated for N steps, where for each adjacent step fi+1=fi+Δf. In this fashion, the optical power response in a total optical bandwidth of N·Δf is measured with a spectral resolution determined by the electronic measuring means.
It will be obvious to those skilled in the art that there are numerous ways of carrying out the above embodiment. For example, the light source can be 1) a wavelength-tunable light source such as a laser that undergoes noise modulation through one of the various methods of producing noise that are known in the art or disclosed herein, or 2) an erbium doped fiber amplifier (EDFA) noise source that is split into N noise sources using, for example, a component known as a wavelength division demultiplexer, or 3) any light source characterized by a randomly varying amplitude and broad spectral bandwidth, and for which the center carrier frequency can be changed. In addition, it will be obvious that the N sequential measurement steps described in this embodiment can instead be carried out in parallel, through the use of a suitable optical means for separating the returning radiation from the target medium into N spectral windows, each of which are measured separately in an electronic measuring means that includes a detector and ESA or other electronic spectral measurement means. It will also be obvious that one or more of the spectral steps can be skipped, so that only a portion of the total optical spectrum width N·Δf will be measured.
Therefore, this invention has certain advantages over other spectral techniques that are applied to EM media. It allows for the acquisition of the spectral response of the medium to optical power signals with extremely high resolution, limited only by the electronic means, and can easily be on the order of 1 Hz or better. The spectral measurement is straightforward and relatively inexpensive. The types of spectral measurements include but are not limited to: spectral changes resulting from single or multiple specular reflections, single or multiple diffuse reflections, absorption, gain, and dispersion, where any of the above take place within or on the surface of the EM medium.
In different embodiments, it is possible to apply an optical delay on the optical path between the illuminating radiation and the detector of the illuminating radiation; by applying an optical delay on the optical path between the illuminating radiation and the detector of the radiation returning from the object or medium; or by applying an optical delay on the optical path between the illuminating radiation and the detector. Any of these methods can be carried out by splitting the illuminating beam into at least two paths whereby the at least two paths are of equal optical delay or of unequal optical delay.
In some of the above embodiments, acquisition of the power signal of the illuminating radiation can be carried out continuously throughout the process of measuring the returning radiation from the medium, or in certain situations it can be measured only once at the beginning of the measurement process, or in certain situations only at certain times during the measurement process. The latter options are possible if the average spectral characteristics and temporal characteristics of the illuminating radiation do not change significantly throughout the said measurement process, so that the signal waveform of the illuminating radiation can be stored electronically and then extracted from memory to be applied as explained in the various embodiments.
It is also to be understood that in some of the embodiments, instead of measuring the power signal of the actual source used as the irradiating radiation, it is possible to substitute in its place a different source having noise statistical characteristics and/or power spectrum that is substantially the same as of that of the actual source used for illuminating the object or medium. So, for example, the object or medium can be irradiated with an irradiation source from the same or different location as the measurement system, and another “local” source which is part of the measurement system is used as described in the various embodiments, to determine the optical power frequency response or impulse response of the object or medium.
It is also to be understood that in some of the embodiments, instead of measuring the power signal of the source used as the irradiating radiation, it is possible to substitute in its place a simulated power signal or spectrum that closely resembles or is identical to the actual irradiating source in terms of the noise statistics or spectrum.
In certain applications it will be advantageous to vary the optical delay of sin(t) and/or of sout(t) before one or both of the optical signals enter the detectors of
In non-limiting embodiments, the electronic means used to determine the PSD spectrum can comprise at least one of the following: an electronic spectrum analyzer (ESA), an electronic correlator circuit, a memory device, a computer, electronic circuitry to carry out any of the required algebraic functions and other signal processing tasks.
Another useful power signal having a useful PSD spectrum can be determined by performing a summation of the power signal of the illuminating radiation and of the power signal of the returning radiation. The summation can be performed by directing at least a portion of the illuminating radiation and at least a portion of the returning radiation onto the same detector, or by summing the power signal of the illuminating radiation and of the returning radiation with an electronic summing circuit or computer. Another useful power signal having a useful PSD spectrum can be determined by performing a subtraction of the power signal of the illuminating radiation and of the power signal of the returning radiation; alternately performing any algebraic calculation that is dependent upon the power signal of the illuminating radiation and the power signal of the returning radiation can be carried out to determine the resulting power signal having a PSD spectrum.
In some embodiments (for example, see step S109 of
For example, it is possible to analyze the difference signal:
s
out(t)=|ρ|2(sin(t)−sin(t−T))
or any other algebraic function of the two signals through electronic means. This may serve to enhance the characterization of the target by improving the depth resolution, signal-to-noise ratio, depth range or other aspects of the measurement technique.
It will be obvious to those skilled in the art that further variations on the above embodiments are possible which will aid in reducing the required electronic bandwidth to values below Δf. In addition, if the target consists of more than one reflection, especially if the number of reflections is known a priori, then suitable signal processing techniques can be utilized for reducing the required bandwidth and determining the delay times to the reflecting surfaces with high accuracy.
Some embodiments relate to a ‘double spectrum technique.’ However, any technique for analyzing a spectral distribution may be used. Thus, in some embodiments, it is possible to characterized optical power frequency response of the object or medium by doing any combination of the following:
a. using electronic means to determine the power spectral density (PSD) spectrum of the illuminating optical radiation from the measured power signal of the illuminating radiation;
b. using electronic means to determine the PSD spectrum of the returning optical radiation from the measured power signal of the returning radiation;
c. dividing the PSD spectrum of the returning radiation by the PSD spectrum of the illuminating radiation to determine the amplitude squared of the power transfer function spectrum.
In some of the above embodiments, acquisition of the power signal of the illuminating radiation can be carried out continuously throughout the process of measuring the returning radiation from the medium, or in certain situations it can be measured only once at the beginning of the measurement process, or in certain situations only at certain times during the measurement process. The latter options are possible if the average spectral characteristics and temporal characteristics of the illuminating radiation do not change significantly throughout the said measurement process, so that the signal waveform of the illuminating radiation can be stored electronically and then extracted from memory to be applied as explained in the various embodiments.
It is also to be understood that in some of the embodiments, instead of measuring the power signal of the actual source used as the irradiating radiation, it is possible to substitute in its place a different source having noise statistical characteristics and/or power spectrum that is substantially the same as of that of the actual source used for illuminating the object or medium. So, for example, the object or medium can be irradiated with an irradiation source from the same or different location as the measurement system, and another “local” source which is part of the measurement system is used as described in the various embodiments, to determine the optical power frequency response or impulse response of the object or medium.
It is also to be understood that in some of the embodiments, instead of measuring the power signal of the source used as the irradiating radiation, it is possible to substitute in its place a simulated power signal or spectrum that closely resembles or is identical to the actual irradiating source in terms of the noise statistics or spectrum.
In certain applications it will be advantageous to vary the optical delay of sin(t) and/or of sout(t) before one or both of the optical signals enter the detectors of
In some embodiments (e.g. related to
Additional Comments
It is obvious that all of the figures herein are only schematic and are missing optical components for launching, collecting and detecting the EM radiation; specific means for measuring the source signal and spectrum, returning signal and spectrum and/or other components that are well-known to those skilled in the art that are necessary for carrying out the embodiments described herein as well as the directional EM beam control for scanning the target area. In addition, although the figures depict configurations whereby the exiting signal is reflected from the object, the invention is not limited to applications based on reflection configurations. It will be obvious to those skilled in the art that, in all embodiments of the invention, the illumination and detection geometry can involve reflection, transmission, or any other type of deflection of the radiation from the target
It is to be understood that in all of the embodiments described herein, it is possible to irradiate the object under test, be it a fiber or any other medium, with two or more EM sources characterized by the random statistics described earlier, in order to enhance the measuring capabilities of the system, These sources can illuminate the medium from the same direction or from different directions. For example, in the optical fiber-based embodiments, it is possible to illuminate the fiber from both ends in order to measure the frequency and/or impulse response as seen from both ends of the fiber. It is also to be understood that if two or more light sources are used, they can be of the same center frequency so that their spectrums' overlap, or substantially of different center frequencies so that their spectrums' partially overlap or do not overlap at all.
In some embodiments, it is possible to employ light that is 1) varying randomly only in phase and not in amplitude, or 2) varying randomly in phase as well as in amplitude (recall that the previous disclosures only discuss amplitude modulation). These phase changes are then measured using some type of interferometer before the detector (as opposed to the previous embodiments where the light enters the detector directly. The signal exiting the detector includes a term that is proportional to cos(øs(t)−ør(t)), where øs(t) is the randomly varying phase signal that exits the medium and enters the interferometer, and ør(t) is the randomly varying reference phase signal that is formed in the interferometer, and is usually a delayed form of øs(t). This reference phase signal can be formed in an interferometer that is after the medium, or it can be formed in an interferometer where the interferometer itself is part of the medium (such as two fibers running along a fence, one fiber is the signal path and the other is the reference path, or in another embodiment only one fiber runs along the fence and the interferometer is formed after the signal exits the signal-forming fiber, or another embodiment where the signal and reference paths are two different modes of a multimode fiber—other embodiments are of course possible).
Another difference between this disclosure and the previous ones is that the processing
A Discussion of
In another embodiment, it is possible to image objects that are behind a medium, such as trees, other foliage, camouflage material or cloud cover, that partially obscures the object.
An experimental setup is shown schematically in
In the first experiment, the reference PSD spectrum of the source was established with the light returning only from plate G1. The spectrum after averaging is shown in
After measuring the reference, spectrum plate G2 was added at a distance of 25 cm. The resulting PSD spectrum and impulse response are shown in
In the next experiment G2 was removed and G3 was inserted at a distance of 50 cm from G1. The resulting spectrum and impulse response are shown in
In the final experiment of this series G2 was reinserted so that all the plates were present. The resulting spectrum and impulse response are shown in
In another experiment the glass plates were replaced with optical fiber of various lengths. The
All of these figures show impulse responses that are in perfect agreement with the expected time-of-flight from the various reflection points along the target.
It is further noted that any of the embodiments described above may further include receiving, sending or storing instructions and/or data that implement the operations described above in conjunction with the figures upon a computer readable medium. Generally speaking, a computer readable medium may include storage media or memory media such as magnetic or flash or optical media, e.g. disk or CD-ROM, volatile or non-volatile media such as RAM, ROM, etc. as well as transmission media or signals such as electrical, electromagnetic or digital signals conveyed via a communication medium such as network and/or wireless links
Having thus described the foregoing exemplary embodiments it will be apparent to those skilled in the art that various equivalents, alterations, modifications, and improvements thereof are possible without departing from the scope and spirit of the claims as hereafter recited. In particular, different embodiments may include combinations of features other than those described herein. Accordingly, the claims are not limited to the foregoing discussion.
| Number | Date | Country | Kind |
|---|---|---|---|
| 203449 | Jan 2010 | IL | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13010810 | Jan 2011 | US |
| Child | 13555505 | US | |
| Parent | PCT/IL2011/000075 | Jan 2011 | US |
| Child | 13010810 | US |
