Patent Application
20170350760
The present invention relates to an optical measurement system. In particular, the present invention relates to a spectrometer for optical measurement including a Fabry-Perot interferometer and a detector. The present invention further relates to a method for analyzing the spectrum of an object. The present invention furthermore relates to a computer readable medium having stored thereon a set of computer implementable instructions.
Optical measurement systems are e.g. used for analyzing properties or material contents of a target. The spectrum of an object, for example a gas or gas mixture, can be measured by using spectrometer comprising a Fabry-Perot interferometer and a detector for monitoring intensity of light transmitted through the Fabry-Perot interferometer. Use of micromechanical technology for producing Fabry-Perot interferometers is common.
A Fabry-Perot interferometer is based on two mirrors, i.e. an input mirror and an output mirror arranged facing the input mirror via a gap. In this document a “mirror” is a structure where there is a layer or a set of layers which reflects light. The pass band wavelength can be controlled by adjusting the distance between the mirrors, i.e. the width of the gap. The Fabry-Perot interferometer may provide a narrow transmission peak, which has adjustable spectral position, and which can be used for spectral analysis. A spectrometer may provide a control signal indicative of the mirror gap. The control signal may be provided e.g. by a control unit, and the mirror gap may be controlled according to the control signal. Alternatively, the control signal may be provided by monitoring the mirror gap, e.g. by using a capacitive sensor. The control signal may be e.g. a digital control signal or an analog control signal. Each spectral position may be associated with a control signal.
The relationship between each spectral position of the transmission peak and a control signal value corresponding to said spectral position may depend e.g. on the operating temperature of the Fabry-Perot interferometer. As changes of temperature of the environment typically affect the operating temperature of the interferometer, temperature drift will occur in the wavelength response of the interferometer. The width of the gap of the interferometer may, for example, change by 1 [nm/° C.]. Instead, maximum tolerance values in some technical measurements allow only changes of the width of the gap of less than 0.05 [nm/° C.].
Document U.S. Pat. No. 5,818,586 describes that a miniaturized spectrometer for gas concentration measurement includes a radiation source for admitting electromagnetic radiation onto the gas to be measured, a detector for detecting the radiation transmitted through or emitted from the gas, an electrically tunable Fabry-Perot interferometer placed in the path of the radiation prior to the detector, control electronics circuitry for controlling the radiation source, the interferometer and the detector. The radiation source, the detector, the interferometer and the control electronics are integrated in a miniaturized fashion onto a common, planar substrate and the radiation source is an electrically modulatable micromechanically manufactured thermal radiation emitter.
Document US 2013/0329232 A1 further discloses controllable Fabry-Perot interferometers which are produced with micromechanical (MEMS) technology. According to the invention the interferometer arrangement has both an electrically tunable interferometer and a reference interferometer on the same substrate. The temperature drift is measured with the reference interferometer and this information is used for compensating the measurement with the tunable interferometer.
An object of certain embodiments of the present invention is to provide an optical measurement system. In particular, an object of certain embodiments is to provide an optical measurement system including a Fabry-Perot interferometer and a detector. Another object of certain embodiments of the present invention is to provide a method for analyzing the spectrum of an object. It is also an object of certain embodiments of the present invention to provide a computer readable medium having stored thereon a set of computer implementable instructions.
These and other objects are achieved by embodiments of the present invention, as hereinafter described and claimed. According to an aspect of the invention, there is provided an optical measurement system comprising:
According to an embodiment, the Peltier element is configured to control a temperature of the interferometer. According to an embodiment, the Peltier element is further configured to control the temperature of the interferometer such that the temperature remains essentially constant. According to another embodiment, the Peltier element is configured to control a temperature of the detector.
In an embodiment, the Peltier element, the detector, and the interferometer are arranged in a cavity located in a housing or a cavity located in a cased structure. In another embodiment, the Peltier element is configured to control a temperature in the cavity. According to an embodiment, the Peltier element is further configured to control the temperature in the cavity such that the temperature remains essentially constant. The Peltier element is attached to a frame which is removably connected to the housing. The housing comprises cooling fins in order to increase the surface area of the housing for optimum heat transfer.
In an embodiment, the system includes at least one circuit board.
In another embodiment, the system comprises one or more than one thermistor.
According to another aspect, the object of the embodiments of the invention can be also achieved by a method for analyzing the spectrum of an object, the method comprising:
According to an embodiment, the effect of a change in temperature of an environment on mechanical dimensions of the interferometer is essentially compensated by means of the Peltier element.
According to another embodiment, the Peltier element is controlled such that a temperature of the detector or the interferometer remains essentially constant.
In an embodiment, the system comprises a filter configured such that a bandwidth of wavelengths can pass the filter. In another embodiment, the bandwidth of wavelengths is a main bandwidth of wavelengths of the Fabry-Perot interferometer. Typically, the bandwidth of wavelengths is in the wavelength range between λ=1 [μm] and λ=2 [μm], λ=1 [μm] and λ=5 [μm], or λ=1 [μm] and λ=10 [μm].
Additionally, according to another aspect, the object of the embodiments of the invention can be also achieved by a computer readable medium having stored thereon a set of computer implementable instructions capable of causing a processor, in connection with the optical measurement system according to any one of claims 1 to 15, to analyze properties or material contents of a radiation source in a measurement area.
Considerable advantages are obtained by means of the embodiments of the present invention. Embodiments of the invention provide an optical measurement system. In particular, certain embodiments provide an optical measurement system including a Fabry-Perot interferometer and a detector. Certain embodiments provide a method for analyzing the spectrum of an object, for example such as a gas or a gas mixture or a liquid. Additionally certain embodiments provide a computer readable medium having stored thereon a set of computer implementable instructions.
According to the embodiments of the present invention, it is possible to achieve high temperature stability since the effect of changes in temperature of the environment on the dimensions of the Fabry-Perot interferometer and/or detector can be compensated to large extent by means of the Peltier element. Changes of the width of the gap of less than 0.05 [nm/° C.] during operation of the optical measurement system can be realized by means of the embodiments of the invention. At the same time, the operational temperature range, i.e. the temperature range of the environment, may be according to a specific embodiment between −10 [° C.] and +70 [° C.], i.e. the temperature of the interferometer and/or detector can be held essentially constant in said operational range. According to certain other embodiments, the operational temperature range may be between +10 [° C.] and +30 [° C.], or between −20 [° C.] and +40 [° C.], for instance. According to a certain embodiment, a temperature of the environment in the range between about 65 [° C.] and 70 [° C.] can be compensated by means of the Peltier element. In this case, the temperature of the Peltier element may be 40 [° C.]±0.05 [° C.]. The power of the optical measurement system is typically less than 1 [W], i.e. power consumption of the system according to the specific embodiment of the present invention is low compared to existing spectrometers operating in a temperature range between 65 [° C.] and +70 [° C.]. Additionally, the structure of the housing and frame according to certain embodiments, i.e. cooling fins and/or wedge shaped portions of the housing as well as form fitting wedge shaped portions of the frame highly support heat exchange. Suprisingly, the measurement by the detector, which is located between the Peltier element and the Fabry-Perot interferometer, is not affected during controlling of the temperature of the interferometer. The system can be adjusted for several temperature ranges by measuring the temperature of the environment and wavelength calibration of the device. Temperature ranges can automatically change and thermal operation can be improved.
The embodiments of the present invention provide a simple and compact structure. An additional reference interferometer is not required, thus reducing costs and production time as well as avoiding problems resulting from calibration of two interferometers. The measurement accuracy and stability can be improved and requirements for packaging are lighter.
For a more complete understanding of particular embodiments of the present invention and their advantages, reference is now made to the following descriptions, taken in conjunction with the accompanying drawings. In the drawings:
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A detector 23 for detecting radiation from a radiation source 24 in a measurement area 25 is fixedly attached to the Peltier element 11. Additionally, an electrically tunable Fabry-Perot interferometer 10 is placed in the path of the radiation prior to the detector 23. According to certain embodiments, the Fabry-Perot interferometer 10, the detector 23, and the Peltier element 11 may be arranged in a cased structure 36 which is not shown in
Further, a second transversal element 7 is attached to the first and second longitudinal elements 8, 9 of the frame 3 by means of screws and/or adhesive 14. A cover plate 24 is additionally attached to the first and second longitudinal elements 8, 9 and the first transversal element 4. The first and second longitudinal elements 8, 9, the first transversal element 4 and the cover plate 24 may be, for example, milled from a solid piece of metal.
The first and second longitudinal elements 8, 9, the first and second transversal elements 4, 7, and the cover plate 24 form a frame 3 having a cavity 12 which is open to one side. The frame 3 is configured to be inserted into a housing 2 of the measurement system 1, which housing 2 is not shown in
The Peltier element 11, the detector 23, and the interferometer 10 are arranged in the cavity 12 of the frame 3. According to the embodiments, the Peltier element 11 is configured to control a temperature of the interferometer 10. According to certain embodiments, the Peltier element 11 is configured to control a temperature of the detector 23. According to other certain embodiments, the Peltier element 11 is configured to control a temperature in the cavity 12. In this case, the Peltier 11 element is, for example, configured to control the temperature in the cavity 12 such that the temperature remains essentially constant.
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Radiation can enter the hermetically sealed cased structure 36 shown through an aperture 32 in which a filter 33 is arranged. The filter 33 is configured such that only a certain bandwidth of wavelengths λ can pass the filter. The bandwidth of wavelengths λ may be, for example, the main bandwidth of the Fabry-Perot interferometer 10. The wavelength range may be, for example, between α=1 [μm] and α=2 [μm]. According to certain other embodiments, the wavelength range may be, for example, between λ=1 [μm] and λ=5 [μm], or λ=1 [μm] and λ=10 [μm]. According to some embodiments, the filter 33 is tuned to a fixed wavelength.
Subsequently, the radiation passes the Fabry-Perot interferometer 10 and is then detected by means of the detector 23. The electrically tunable Fabry-Perot interferometer 10 comprises a first semi-transparent mirror and a second semi-transparent mirror, which are arranged to form an optical cavity of the interferometer. According to certain embodiments, the maximum change of the width of the gap is less than 0.2 [nm/° C.], less than 0.1 [nm/° C.], or less than 0.05 [nm/° C.] during operation of the optical measurement system 1. The Fabry-Perot interferometer may provide a narrow transmission peak, which has adjustable spectral position, and which can be used for spectral analysis. The spectral position of the transmission peak may be changed by changing the distance between the mirrors. The Fabry-Perot interferometer 10 may have an adjustable mirror gap. The spectral position of the transmittance peak may be changed according to the control signal. The control signal may be e.g. a voltage signal, which is applied to a piezoelectric actuator of the Fabry-Perot interferometer 10 in order to change the mirror gap of the Fabry-Perot interferometer. The control signal may be e.g. a voltage signal, which is applied to electrodes of an electrostatic actuator in order to change the mirror gap of the Fabry-Perot interferometer 10.
The detector 23, for example an infrared-detector, may comprise a spacer in order to arrange the detector 23 at a specific distance from the Fabry-Perot interferometer 10. According to certain embodiments, materials of components used in the cased structure 36 or located adjacent to each other have the same coefficient of thermal expansion or at least a coefficient of same order. The spacer may be, for example, made from silicon based on ceramic material. Typically, the detector 23 is configured to detect the filtered wavelengths. According to certain embodiments, the detector 23 is configured to detect at least the bandwidth of wavelengths of the Fabry-Perot interferometer 10. Since the noise level of an infrared-detector increases with increasing temperature, the temperature of the detector is stabilized to an accuracy of less than 0.5 [° C.], less than 0.3 [° C.], less than 0.1 [° C.], or less than 0.05 [° C.] according to certain embodiments.
Further, a submount 34 is arranged between the detector 23 and the Peltier element 11. The submount 34 may be, for example, made from ceramic material.
The Peltier element is configured to control the temperature T2 of the interferometer 10. According to a certain embodiment, the Peltier element is controlled such that the temperature T2 of the interferometer 10 remains essentially constant. An essentially constant temperature according to the present invention means that the temperature does not change more than 1 [° C.], preferably not more than 0.5 [° C.], even more preferably not more than 0.1 [° C.], or more than 0.05 [° C.]. In this case, the temperature T2 of the interferometer 10 may be, for example, T2=20 [° C.], T2=22 [° C.], T2=24 [° C.], T2=38 [° C.], T2=40 [° C.], T2=42 [° C.], or any other predetermined temperature. According to certain other embodiments, the temperature of the interferometer 10 may vary in a specific range, for example between T2=22.8 [° C.] and T2=23.2 [° C.], or between T2=39.95 [° C.] and T2=40.05 [° C.]. In a certain embodiment, the Peltier element is configured to control the temperature of the cavity 38 in the cased structure 36.
The cased structure 36 may be fixedly attached to the first transversal element 4 of the frame 3 by means of use of an adhesive such as a thermally conductive adhesive, for example an epoxy, and simultaneous alignment. Heat exchange from inside the cavity 38 of the cased structure to outside the cavity 38 is effective without deformation of the cased structure 36 due to temperature change. The adhesive used may be flexible according to certain embodiments. In other cases, the cased structure 36 may be welded to the frame 3. Typically, only the surface of the cased structure 36 which is situated on the opposite side of the aperture 32 is connected to the frame 3 in order to avoid a heat return flow into the cased structure 36. Additionally, the Fabry-Perot interferometer 10, the detector 23, and the Peltier element 11 are connected to electric wires 18 which can be guided through openings 30 from the first side 5 of the first transversal element 4 to the second side 6 of the first transversal element 4. According to certain embodiments, one or more thermistors are arranged in the cased structure 36 for monitoring a temperature gradient in the cased structure 36. Arrangement of, for example, two thermistors improves the capability to stabilize the temperature T2 of the interferometer 10.
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According to certain embodiments, a main circuit board 35 is attached to the housing 2. The main circuit board 35 is connected to the circuit board 17 attached to the frame 3 by electrical wires. The main circuit board 35, the circuit board 17, and the electrical wires 18 connected to the Peltier element 11, the detector 23 as well as the Fabry-Perot interferometer 10 form a control electronics circuitry for controlling the Peltier element 11, the interferometer 10, and the detector 23.
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According to certain other embodiments, the optical measurement system 1 further includes a computerized device 28, such as a personal computer or a mobile computing device, which is connected to the main circuit board 18. The computing device 28 includes a computer readable medium having stored thereon a set of computer implementable instructions capable of causing a processor, in connection with the optical measurement system 1, to analyze properties or material contents of the radiation source 25 in the measurement area 26.
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According to a certain embodiment, the effect of a change in temperature of an environment on mechanical dimensions of the interferometer is compensated by means of the Peltier element. According to another certain embodiment, the Peltier element is controlled such that a temperature of the detector and/or the interferometer remains essentially constant.
Of course, the electrically tunable Peltier element can be controlled before placing the electrically tunable Fabry-Perot interferometer in the path of the radiation emitted by the radiation source in the measurement area or before detecting the radiation by means of a detector.
Although the present invention has been described in detail for the purpose of illustration, various changes and modifications can be made within the scope of the claims. In addition, it is to be understood that the present disclosure contemplates that, to the extent possible, one or more features of any embodiment may be combined with one or more features of any other embodiment.
It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.
Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.
As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.
Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.
While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.
The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, that is, a singular form, throughout this document does not exclude a plurality.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20145969 | Nov 2014 | FI | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FI2015/050765 | 11/5/2015 | WO | 00 |
