JP2006220623A - Fabry-perot interferometer and infrared sensor apparatus using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Fabry-Perot interferometer for simultaneously transmitting an infrared wavelength having a characteristic for absorbing a gas whose concentration is sensed even if a plurality of components are contained in the gas whose concentration is sensed. <P>SOLUTION: The Fabry-Perot interferometer comprises a first interferometer mirror 20 provided on and fixed to a substrate 10, and a second interferometer mirror 30 disposed and facing the first interferometer mirror 20 through a gap 60. At least one of the first and second interferometer mirrors 20, 30 is formed so as to have a step 50. A plurality of different gap lengths are set between the first and second interferometers 20, 30. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a Fabry-Perot interferometer and an infrared sensor device using the same.

  As an infrared sensor device for measuring the gas concentration, for example, a device using a Fabry-Perot interferometer as shown in Patent Document 1 is known. When a gas whose gas concentration is to be detected (gas to be measured) is irradiated with infrared rays, the gas to be measured absorbs infrared rays having a specific wavelength from the wavelength contained in the irradiated infrared rays due to the component concentration contained in the gas to be measured. is there. Utilizing such a property, the Fabry-Perot interferometer, for example, includes infrared light having a wavelength that is absorbed by the gas to be measured and infrared light having a wavelength (reference wavelength) that is not absorbed by any component included in the gas to be measured. Configured to be transparent.

  An example of such a Fabry-Perot interferometer is shown in FIG. The Fabry-Perot interferometer 5c shown in FIG. 5 is formed on the substrate 10 by applying a potential difference (wavelength selection voltage) from the power source 82 to the electrodes 80 provided on the interferometer mirrors 20 and 30 at predetermined timings. An electrostatic force is generated between the first interferometer mirror 20 and the second interferometer mirror 30. Then, the second interferometer mirror 30 is displaced in the direction of the first interferometer mirror 20 by a predetermined displacement at every timing when the wavelength selection voltage is given. As a result, the gap length t between the interferometer mirrors 20 and 30 changes to the desired gap length T.

These gap lengths t and T are set so as to transmit the above-described absorption wavelength infrared rays and reference wavelength infrared rays, respectively. Thereby, when the incident infrared ray 70 enters the Fabry-Perot interferometer 5 c, the absorption wavelength infrared ray and the reference wavelength infrared ray are extracted as the transmission infrared ray 75 at different timings. If the absorption wavelength infrared ray and the reference wavelength infrared ray are detected by the infrared sensor 6 and their intensities are compared, the concentration of the gas to be measured can be obtained.
JP-A-6-241993

  By the way, the component concentration contained in the gas to be measured continues to change every moment. In order to adapt the Fabry-Perot interferometer to such a constantly changing component concentration, it is necessary to change the gap length by applying a wavelength selection voltage between the electrodes 80 provided on the interferometer mirror at a predetermined timing. . For this reason, the second interferometer mirror 30 vibrates at a predetermined cycle.

  However, when detecting the infrared rays of a plurality of wavelengths by changing the gap length of the Fabry-Perot interferometer 5c at every predetermined timing, the time until the detection becomes long. Such a problem becomes more prominent as the number of infrared rays to be detected increases. Further, when the second interferometer mirror 30 is constantly vibrated, the second interferometer mirror 30 is fatigued.

  When the flexibility and strength of the second interferometer mirror 30 are reduced due to this fatigue, the second interferometer mirror 30 is likely to be plastically deformed or damaged. When the second interferometer mirror 30 is plastically deformed, it leads to a decrease in the reaction speed and a change in the correlation between the given wavelength selection voltage and the amount of displacement. If the second interferometer mirror 30 is damaged, the Fabry-Perot interferometer 5c no longer performs its function.

  Therefore, the present invention has been made in view of the problems as described above, and the object of the present invention is to make the incident infrared ray 70 pass through the Fabry-Perot interferometer without vibrating the interferometer mirror. Another object of the present invention is to provide a Fabry-Perot interferometer capable of transmitting infrared light of a plurality of specific infrared wavelengths and an infrared sensor device using the same.

  In order to solve the above-mentioned problem, a Fabry-Perot interferometer according to claim 1 is provided on a substrate, a first interferometer mirror fixed to the substrate, a first interferometer mirror and a gap therebetween. And at least one of the first and second interferometer mirrors is formed to have a step, and a plurality of interferometer mirrors are arranged between the first and second interferometer mirrors. A different gap length is set.

  According to the first aspect of the present invention, since a plurality of gap lengths having different lengths can be set, when the irradiated infrared light transmits Fabry-Perot interference, the set gap length and the number of gap lengths are set. In response to this, it is possible to simultaneously transmit infrared light having a plurality of specific infrared wavelengths.

  The Fabry-Perot interferometer according to claim 2 is characterized in that the step is formed in a step shape. According to the second aspect of the present invention, since more portions having different gap lengths are set in the gap, infrared light having more specific infrared wavelengths is simultaneously transmitted according to the gap length. Can be made.

  An infrared sensor device according to a third aspect includes an infrared light source, an infrared sensor corresponding to a plurality of gap lengths, and the above-described Fabry-Perot interferometer according to the present invention.

  As described in claim 3, by applying the Fabry-Perot interferometer according to the present invention to an infrared sensor device, an infrared sensor device capable of simultaneously measuring a plurality of components of a gas to be measured can be obtained.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a configuration diagram of an infrared sensor device 100 of the present invention. The infrared sensor device 100 includes a sample cell 4 provided with an inlet 2 and an outlet 3 for a gas to be measured, an infrared light source 1 that is provided inside the sample cell 4 and emits irradiated infrared light that irradiates the gas to be measured; Fabry-Perot interferometer 5 that transmits infrared rays of a desired wavelength, infrared sensors 6a and 6b that detect the intensity of transmitted infrared rays 71 and 72 that have passed through Fabry-Perot interferometer 5, and output signals from infrared sensors 6a and 6b And an output terminal 7 for outputting.

  In the infrared sensor device 100, the gas to be measured is introduced into the sample cell 4 from the inlet 2 and out of the outlet 3. The infrared light source 1 irradiates incident infrared light 70 toward the measurement gas.

  The incident infrared ray 70 is absorbed by the gas to be measured that fills the optical path of the incident infrared ray 70 from the infrared light source 1 to the Fabry-Perot interferometer 5.

  The Fabry-Perot interferometer 5 transmits only infrared light having a wavelength corresponding to the gap length. In this embodiment, as will be described in detail later, infrared light having a wavelength that is not absorbed by the gas to be measured and infrared light having a wavelength that is absorbed by the gas to be measured are simultaneously transmitted through the Fabry-Perot interferometer 5. As described above, two types of gap lengths are set in the Fabry-Perot interferometer 5. For this reason, one of the transmitted infrared lights 71 and 72 transmitted through the Fabry-Perot interferometer 5 is used as the reference infrared light, and the other is used as the measurement infrared light. Can be sought. In addition, when the infrared light source 1 irradiates infrared light with substantially constant intensity, the reference infrared light is not necessary. In this case, the Fabry-Perot interferometer 5 can be used to simultaneously measure the concentrations of two kinds of gas components contained in the gas to be measured.

  FIG. 2 is a schematic cross-sectional view for explaining the basic configuration of the Fabry-Perot interferometer 5 of the present invention. The Fabry-Perot interferometer 5 includes a substrate 10, a first interferometer mirror 20 formed to have a step 50, and a second interferometer mirror 30. Therefore, gap lengths t1 and t2 having different lengths are set between the first interferometer mirror 20 and the second interferometer mirror 30 by the step 50 formed in the first interferometer mirror 20. A gap 60 is formed as described above.

  The substrate 10 is made of a material that transmits infrared rays, such as silicon or germanium.

  The first and second interferometer mirrors 20 and 30 are formed of an infrared transmitting material on the substrate 10 through the gap 60 described above so as to have a predetermined film thickness.

  As an infrared transmitting material for forming the first and second interferometer mirrors 20 and 30, for example, a silicon compound alone such as polysilicon, silicon oxide, silicon nitride, or the like can be used. This silicon compound is deposited as a single layer film or a multilayer film on the substrate 10 so as to have a predetermined film thickness. When the first and second interferometer mirrors 20 and 30 are formed of multilayer films, the materials of the respective thin films may be the same or different (for example, polysilicon and silicon oxide).

  The first interferometer mirror 20 has a step 50 formed by temporarily depositing a silicon compound on the substrate 10 so as to have a film thickness corresponding to the gap length t2, and then partially removing it by etching. Form. Alternatively, the step 50 of the first interferometer mirror 20 is temporarily deposited with a silicon compound so as to have a film thickness corresponding to the gap length t1, and then the silicon compound is equivalent to the step 50 only in a part of the region. It is also possible to form the film by depositing a film having a desired thickness.

  Further, the silicon compound for forming the second interferometer mirror 30 is deposited so as to face the first interferometer mirror 20 through, for example, a planarized oxide that can be removed by etching. . Thereafter, a through hole reaching the oxide layer is formed around the second interferometer mirror 30, and an etching solution is introduced into the through hole, whereby the gap 60 is formed.

  The film thicknesses d1 and d2 of the first interferometer mirror 20 and the second interferometer mirror 30 are set such that the center wavelength of the incident infrared ray 70 emitted from an infrared light source (not shown) is λ. They are formed so as to have optical film thicknesses (nd) that substantially satisfy the conditions of λ / 4 = n1 · d1 (n1: refractive index) and λ / 4 = n2 · d2 (n2: refractive index), respectively. .

  The infrared sensors 6a and 6b detect the intensities of transmitted infrared rays 71 and 72 in which infrared rays having a specific wavelength are absorbed by the gas to be measured. Infrared sensors 6a and 6b are desirably arranged with a predetermined interval in order to avoid interference between transmitted infrared rays 71 and 72 and to improve detection accuracy.

  By the way, in the transmitted infrared rays 71 and 72 detected by the infrared sensors 6a and 6b, the wavelength of the transmitted infrared ray 71 transmitted through the gap interval length t1 is λ1, and the transmitted infrared ray 72 is transmitted through the gap interval length t2. When the wavelength is λ2, 2 · n1 · t1 = N · λ1 (n1: refractive index, N: integer), 2 · n2 · t2 = N ′ · λ2 (n2: refractive index, N ′: integer) Satisfy the relationship.

  In the present embodiment, since the wavelengths λ1 and λ2 of the transmitted infrared are clearly defined as in the above equation, either λ1 or λ2 can be used as the reference wavelength.

As described above, in the present embodiment, the Fabry-Perot interferometer 5 is formed such that the first interferometer mirror 20 has the step 50, and a plurality of different gap lengths t1, t2 are provided in the gap 60. Is set. The Fabry-Perot interferometer 5 can simultaneously extract infrared rays having two wavelengths according to the set gap lengths t1 and t2.
(Second Embodiment)
Next, an infrared sensor device according to a second embodiment will be described.

  In the infrared sensor device 100 according to the first embodiment described above, the Fabry-Perot interferometer has two gap lengths t1 and t2. In the infrared sensor device according to the present embodiment, three types of gap lengths are set in the gap 60 of the Fabry-Perot interferometer 5a shown in FIG. 3 in order to simultaneously detect infrared rays having many wavelengths. To do.

  A Fabry-Perot interferometer 5 a shown in FIG. 3 includes a substrate 10, a first interferometer mirror 20 formed to have a stepped step 51, and a second interferometer mirror 30.

  Due to the step 51 formed stepwise on the first interferometer mirror 20, there are three gap lengths t1 of different lengths between the first interferometer mirror 20 and the second interferometer mirror 30. A gap 60 is formed so that t2 and t3 are set.

  The first interferometer mirror 20 once deposits a silicon compound on the substrate 10 so as to have a film thickness corresponding to the gap length t3. Next, a part thereof is etched away so as to have a film thickness corresponding to the gap length t2. Next, a part of the gap length t2 is removed by etching so that the film thickness corresponds to the gap length t1. By such a process, the step 51 formed in a step shape can be obtained.

  Alternatively, a silicon compound is once deposited on the first interferometer mirror 20 so as to have a film thickness corresponding to the gap length t1. Next, a silicon compound is deposited so as to have a film thickness corresponding to the gap length t2 in the region of the silicon compound layer deposited so as to have a film thickness corresponding to the gap length t1. Next, a silicon compound is deposited in the region of the silicon compound layer deposited so as to have a film thickness corresponding to the gap length t2, and further to have a film thickness corresponding to the gap length t3. Is also possible.

Therefore, the Fabry-Perot interferometer 5a can simultaneously extract infrared rays having three wavelengths according to the set gap lengths t1, t2, and t3. If the Fabry-Perot interferometer 5 of the infrared sensor device 100 shown in FIG. 1 is replaced with the Fabry-Perot interferometer 5b, three component concentrations contained in the gas to be measured can be measured simultaneously. Note that if the number of steps 51 is increased, the concentration of components that can be measured simultaneously can be further increased.
(Third embodiment)
Next, an infrared sensor device according to a third embodiment will be described.

  The Fabry-Perot interferometer 5b shown in FIG. 4 forms a step 50 on the first interferometer mirror 20 and is positioned on the second interferometer mirror 30 via the gap 60 at a position facing the step 50. The step 50 is further formed with a step 52 having a different size.

  By forming the steps 50 and 52 in this way, three gap lengths t1, t2, and t3 can be set in the gap 60. Accordingly, the Fabry-Perot interferometer 5b can simultaneously extract infrared rays having three wavelengths according to the gap lengths t1, t2, and t3 when the irradiated infrared ray 70 passes through the Fabry-Perot interferometer 5b. Further, when the steps 50 and 52 are increased to form a step shape, the infrared wavelength that can be simultaneously absorbed by the Fabry-Perot interferometer 5b can be further increased.

  Note that the silicon compound for forming the second interferometer mirror 30 having the step 52 was deposited in order so as to have a film thickness corresponding to the gap lengths t1, t2, and t3, which can be removed by etching. It is laminated so as to face the first interferometer mirror 20 through the oxide. Thereafter, a through hole reaching the oxide layer is formed around the second interferometer mirror 30, and an etching solution is introduced into the through hole, whereby the gap 60 is formed.

  As described above, in the Fabry-Perot interferometer adopting the configuration of the present invention, at least one of the first interferometer mirror 20 and the second interferometer mirror 30 has the steps 50 and 52. Therefore, a plurality of different gap lengths are set in the gap 60. The Fabry-Perot interferometer can simultaneously transmit infrared rays having a plurality of specific wavelengths according to the gap length when the irradiated infrared rays are transmitted.

  If the Fabry-Perot interferometer 5b of this embodiment is replaced with the Fabry-Perot interferometer 5 of the infrared sensor device 100 shown in FIG. 1, three component concentrations contained in the gas to be measured can be measured simultaneously. If the number of steps 50 or 52 is increased, the concentration of components that can be measured simultaneously can be further increased.

  Although the best mode for carrying out the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. is there. In the invention according to the dependent claims of the present invention, a part of the constituent features of the dependent claims can be omitted.

Configuration diagram of infrared sensor device of the present invention Sectional drawing of the Fabry-Perot interferometer according to the first embodiment of the present invention Sectional view of a Fabry-Perot interferometer according to a second embodiment of the present invention Sectional view of a Fabry-Perot interferometer according to a third embodiment of the present invention Sectional view schematically showing the concept of operation of a conventional Fabry-Perot interferometer

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Infrared light source 2 Gas inlet to be measured 3 Gas outlet to be measured 4 Sample cell 5, 5a, 5b, 5c Fabry-Perot interferometer 6, 6a, 6b, 6c Infrared sensor 7 Output terminal 10 Substrate 20 First interferometer mirror 30 Two interferometer mirrors 50, 51, 52 Stepped portion 60 Gap 70 Incident infrared rays 71, 72, 73, 74, 75 Transmitted infrared ray 80 Electrode 82 Power supply 100 Infrared sensor device

Claims (3)

A first interferometer mirror provided on the substrate and fixed to the substrate;
A first interferometer mirror and a second interferometer mirror disposed opposite to each other with a gap therebetween,
At least one of the first and second interferometer mirrors is formed to have a step, and a plurality of different gap lengths are set between the first and second interferometer mirrors. Fabry-Perot interferometer.   The Fabry-Perot interferometer according to claim 1, wherein the step is formed in a step shape. A Fabry-Perot interferometer according to claim 1 or 2,
An infrared light source that emits infrared light toward the Fabry-Perot interferometer;
A plurality of infrared sensors each detecting infrared light transmitted through a plurality of different gap length portions in the Fabry-Perot interferometer;
An infrared sensor device comprising:

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