The present invention generally relates to environment sensing or detecting, and more particularly relates to optical-based systems and methods for detecting the presence of a specific material, analyte, or agent.
In recent years, the number of uses for devices with the ability to detect various substances has increased dramatically. In particular, greater emphasis has been placed on national homeland security, including the detection of various threats to human populations. Detecting or sensing the presence of undesirable hazardous materials in the environment, such as biological or chemical agents and sources of radioactivity, has become a priority. Such hazardous materials may be found in shipping containers, buildings, airports, or other locations and may be directed at inflicting civilian, as well as military, casualties. As such, there is a need to provide small, affordable devices that are capable of accurately detecting a wide range of hazardous materials.
Accordingly, it is desirable to provide a sensor capable of detecting biological agents, chemical agents, and/or radioactive materials. In addition, it is desirable to provide a sensor for detecting the presence of multiple and different hazards while minimizing the package size and manufacturing costs of the sensor. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.
In one embodiment, an apparatus for detecting an agent is provided. The apparatus includes a substrate, a waveguide on the substrate, a light source coupled to the waveguide and configured to emit light into the waveguide, a photo-detector coupled to the waveguide and configured to detect light, an optical coupler on the substrate and configured to direct a first portion of light propagating from the waveguide towards the photo-detector and to direct a second portion of the light propagating from the waveguide into a second waveguide, the second waveguide and the optical coupler forming a resonator, a substance being at least one of embedded within the waveguide and adjacent to the waveguide, the substance being reactive to the agent, and a processor in operable communication with the photo-detector to detect a change in a resonance lineshape of the resonator caused by said reaction of the substance to the agent.
In another embodiment, an apparatus for detecting an agent is provided. The apparatus includes a substrate, a waveguide having first and second opposing ends on the substrate, a light source on the substrate being operable to emit light into the waveguide, first and second photo-detectors on the substrate being arranged to capture light and configured to generate a signal representative thereof, first and second optical couplers on the substrate, the first optical coupler being arranged to direct at least some of the light propagating from the first end of the waveguide towards the first photo-detector and direct at least some of the light propagating from the first end of the waveguide back into the waveguide, the second optical coupler being arranged to direct at least some of the light propagating from the second end of the waveguide towards the second photo-detector and direct at least some of the light propagating from the second end of the waveguide back into the waveguide, the waveguide and the first and second optical couplers at least partially forming a resonator, a material being at least one of embedded within and adjacent to at least a portion of the waveguide having a substance embedded therein, the substance being reactive to the agent, wherein the agent is one of a biological, chemical, and biochemical agent, and a processor on the substrate and in operable communication with the first and second photo-detectors and configured to detect a change in a resonance lineshape of the resonator caused by said reaction of the substance to the agent.
In another embodiment, a method for detecting an agent is provided. A waveguide having first and second opposing ends is formed on a substrate. A substance is positioned at least one of within the waveguide and adjacent to the waveguide. The substance is reactive to the agent. Light is directed into the first end of the waveguide. The light propagates through the waveguide and from the second end thereof. A first portion of the light propagating from the second end of the waveguide is directed back into the waveguide to be emitted from the first end thereof. A second portion of the light propagating from the second end of the waveguide is captured. A first portion of the light propagating from the first end of the waveguide is directed back into the waveguide towards the second end thereof, the waveguide at least partially forming a resonator. A second portion of the light propagating from the first end of the waveguide is captured. A signal representative of a change in a resonance lineshape of the resonator caused by said reaction of the substance to the agent is generated.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and
The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. It should also be noted that
An apparatus and method are provided for detecting an agent, such as a hazardous material (e.g., biological, chemical, and biochemical agents) in an environment. The apparatus includes a substrate, a waveguide on (or in) the substrate, a first and second reflector formed on or near the first and second ends of the waveguide, a light source and photo-detector coupled to the waveguide, and a material adjacent to (or near) the waveguide. In one embodiment, reflectors are formed on or near the ends of the waveguide. The tunable wavelength light source is configured to emit light into the waveguide which reflects multiple times from both reflectors, thus forming an optical resonator. The photo-detector is configured to detect light escaping the waveguide through one of the reflectors. A substance is embedded within the material. The substance is reactive to the agent such that when the material is exposed to the agent, the resonance lineshape and/or the free spectral range (FSR) of the optical resonator is changed. The change in the FSR or lineshape is measured by changing the wavelength of the laser and monitoring the photo-detector. Alternatively, the material is omitted and a substance is embedded within the waveguide. The substance is reactive to the agent such that when the waveguide is exposed to the agent, the resonance lineshape and/or the free spectral range (FSR) of the optical resonator is changed. The change in the FSR is measured by changing the wavelength of the laser and monitoring the photo-detector. The light detected by the photo-detector changes its intensity when the laser wavelength is swept across over the cavity's FSR. By forming the waveguide on the substrate, as opposed to, for example, utilizing an optical fiber, a smaller, cheaper, and more reliable sensor may be provided.
In one embodiment, the substrate 12 is substantially square (or rectangular) with a side length 26 of, for example, less than 4 cm, or between 1 and 3 cm. Looking ahead to
Referring again to
Still referring to
The first and second photo-detectors 18 and 20 are positioned on the substrate 12 near a central portion thereof. In a preferred embodiment, the first and second photo-detectors 18 and 20 each include a photodiode having a germanium-doped region formed on the substrate 12. In another embodiment, the photo-detectors 18 and 20 include discreet photo-detector chips made of, for example, silicon, germanium, or indium gallium arsenide phosphide (InGaAsP). As shown in
The controller 22 (or processing subsystem), in one embodiment, is formed on or within the substrate 12, and as will be appreciated by one skilled in the art, may include electronic components, including various circuitry and/or engraved circuits (e.g., a microprocessor and a power supply), such as an Application Specific Integrated Circuit (ASIC) and/or instructions stored on a computer readable medium to be carried out by the microprocessor to perform the methods and processes described below. As shown, the controller 22 is in operable communication with and/or electrically connected to the light source, the first and second photo detectors 18 and 20, and the transmitter 24. The transmitter 24 is formed on the substrate 12 and includes, for example, a radio frequency (RF) transmitter, as is commonly understood.
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During operation, the sensor 10 is placed in an environment in which the detecting of a particular agent (i.e., the agent to which the particular indicator substance is sensitive) is desired (e.g., a shipping container, a building, on a soldier, etc.). The controller 22 activates the light source 14 to emit laser light towards the reflector 50. A portion of the light emitted from the light source 14 is transmitted by the reflector 50, focused by the lens 52, and enters the first end 38 of the waveguide 16. Referring to
When the sensor 10, or more particularly the polymeric material 44, is exposed to the particular agent to which the indicator 46 is sensitive, the indicator 46 undergoes a chemical change such that the effective index of refraction of the polymeric material 44 or the optical loss of the polymeric material 44 is altered. Thus, the FSR and/or the Finesse of the cavity is altered. The FSR and/or Finesse of the cavity is monitored by sweeping the wavelength of the laser over a range larger than the FSR of the cavity and monitoring the output of the photodiodes.
In one embodiment, exposure of the polymeric material 44 to the particular agent results in a change (e.g., an increase) in the index of refraction or the loss of the polymeric material 44, such that the coupling of the evanescent wave extending into the polymeric material 44 changes, resulting in more or less optical loss of the waveguide 16. Thus, the Finesse of the cavity is altered. The FSR and Finesse of the cavity can be established by sweeping the laser wavelength over the FSR of the cavity and monitoring the optical power emitted from the second end 40 of waveguide 16 with the second photo detector 20. Determining the frequency separation of two adjacent peak intensities will yield the FSR of the cavity. Measuring the width of the peaks in optical power will yield the FWHM of the resonance peaks and from this the Finesse of the cavity is calculated. The controller 22, or the processor therein, monitors and compares the FSR and Finesse of the cavity. When the FSR or Finesse changes by a predetermined amount, the controller 22 generates an alarm signal. The alarm signal is sent to the transmitter 24 where it may be transmitted via radio waves to a user or a computing system that is monitoring the sensor 10.
In the embodiment shown in
As shown in
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During operation, the sensor 60 is placed in an environment in which the detection of the particular agent is desired. Referring to
The transmitted wave (i.e., the light captured by the second photo-detector 78) is a fraction of, and derived from, the recirculating light wave inside the first waveguide, or the resonator, 68. As the frequency of the light is detuned away from the resonance of the resonator 68, the transmitted portion becomes very small and only the reflected portion impinges on the first photo-detector 76, indicating a maximum intensity with very little destructive interference. As the frequency of the light is scanned through the center of the resonator resonance, the transmitted wave is maximized for the resonator 68 and it produces a maximum destructive interference with the reflected wave, thus providing a resonance dip having a minimum that is indicative of the resonance center.
To observe the resonance center-frequency of the resonator 68, the intensity at either the first photo-detector 76 or the second photo-detector 78 may be measured or a standard synchronous detection technique may be used. In the case of synchronous detection, the input light beam is sinusoidally phase-modulated, and therefore, frequency modulated at a frequency (fm) to dither the input beam frequency across a resonance lineshape as measured by the photo-detectors 76 and 78. For example, the controller (or electronic circuitry) 80 may demodulate the output of the second photo-detector 78 at fm to measure the resonance center indicated by the light output of the circulating light beam. At a line center of the resonance lineshape, or the resonance center, the photo-detectors 76 and 78 detect a minimum output at the fundamental detection frequency fm and detect a maximum on either side of the lineshape near where the slope of the lineshape is greatest.
When the resonator 68 is off-resonance, an intensity signal maximum is observed at detector 76, but the signal at fm is substantially zero. To observe the line width of the resonance lineshape, the frequency of the light source 64 is monotonically scanned such that the light intensity signal on the second photo-detector 78 experiences at least a sequence of observing a half maximum followed by the maximum, and then another half maximum.
Alternatively, a second measure of the lineshape width may be measured by monitoring the frequency difference between maxima of the demodulated signal at fm, as the frequency of the light source 64 is scanned monotonically. In such a case, a measurement of the frequency width of the resonance between points of highest slope is proportional to the resonator line width, and thus proportional to the loss of the resonator 68. The light source 64 frequency excursion from half-maximum to half maximum (e.g., between points of highest slope) is the resonator line width (i.e., proportional to the resonator line width), which is indicative of the loss within the waveguide 68 and a measure of the presence of a hazardous material. Widening of the line width represents the presence of such an agent, or hazardous material, to which the particular indicator substance 95 (
Referring to
One advantage is that because the circuitry and the optical components are formed on a single substrate, in which conventional semiconductor processing techniques may be used, a small and relatively inexpensive hazardous material sensor is provided. Another advantage is that because the waveguide is formed on the substrate itself, along with the other components, the overall size of the device may be even further reduced, while improving durability and reliability.
Other embodiments may utilize radioactively-sensitive dopants, such as phosphorous (P) or boron (B), which are sensitive to at least one of alpha, beta, and gamma particles, and may be embedded within the waveguides themselves (i.e., within core 42 in
It should be understood that various types of optical resonators may be used which utilize waveguides formed in various ways (e.g., waveguides formed on glass, waveguides embedded in LiNbO3, and waveguides formed from a cavity such as an etalon). As is commonly understood cavities used may be, for example, linear or standing wave cavities (e.g., formed by making the ends of the cavity reflective) and ring resonators.
As mentioned briefly above, the Finesse may be measured by sweeping the laser wavelength and monitoring the optical power “leaking” out of the cavity (i.e. looking at the signal from the second photo-detector). After the frequency of the laser is swept more than one FSR of the cavity, the frequency gap between peaks in the output of the cavity (Δλ). The laser may then be swept to measure the linewidth of the resonance peaks. The linewidth used may be the full width and half max (FWHM) of the peaks (δλ) (i.e., the frequency width of the peaks at half of the maximum amplitude of the peaks). The Finesse may then be calculated by taking the ratio of Δλ/δλ. As such, changes in optical loss and/or index of refraction may change the line width and the FSR, and thus the Finesse.
The indicator substance may be on the outside of the waveguide, such as in a material that is adjacent to the waveguide. Such a use of the indicator substance may influence the evanescent coupling of the guided wave and increase the loss in the cavity, which may in turn change the Finesse of the cavity. If the indicator substance is embedded into the waveguide, when exposed to the analyte it is conceivable that the index of refraction in the waveguide may change without causing additional loss. In such an embodiment, the FSR may change and it may not be necessary to measure the Finesse.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.