JP4457455B2 - Fabry-Perot filter and infrared gas analyzer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wavelength selective infrared detecting element used in a gas analyzer that measures the gas concentration in the atmosphere or the like using infrared rays.
[0002]
[Prior art]
In gas analysis, a non-dispersive infrared gas analyzer (Non-Dispersive InfraRed) gas analyzer that measures the gas concentration by detecting the amount of absorption by utilizing the difference in the wavelength of infrared rays absorbed depending on the type of gas. Hereinafter, an NDIR gas analyzer) is used.
[0003]
7 to 11 are configuration diagrams of a conventional NDIR gas analyzer.
In the following, carbon dioxide having an infrared absorption wavelength peak of about 4.25 μm will be described as a gas to be measured.
[0004]
FIG. 7 shows a single-light single-wavelength NDIR gas analyzer, which includes a sample cell 20 to which a gas is supplied, a light source 21, a filter 22, and an infrared detector 23.
In this case, the filter 22 selects and transmits infrared rays having a wavelength in the vicinity of 4.25 μm in accordance with the carbon dioxide absorption characteristics as shown in FIG.
And the infrared detector 23 measures the density | concentration of to-be-measured gas by detecting the infrared rays which permeate | transmitted the filter 22,
[0005]
FIG. 8 shows a single-light two-wavelength comparison NDIR gas analyzer. As shown in FIG. 13, a filter 22 that matches the absorption characteristics of carbon dioxide and a filter that transmits infrared light having a wavelength in the vicinity of about 3.9 μm as reference light. 24, two wavelengths are selected, and the selected infrared rays are detected by infrared detectors 23 and 25, respectively.
In this case, a change with time of the output signal due to deterioration of the light source 21 or contamination of the sample cell 20 can be corrected by comparison with the measured absorption characteristic of the reference light.
[0006]
FIG. 9 is a single-light two-wavelength comparison NDIR gas analyzer. Two wavelengths are selected by a filter 22 that matches the absorption characteristics of carbon dioxide formed on the disk 26 and a filter 24 for reference light, and are selected by the filter. Infrared rays are detected by an infrared detector 23, respectively.
In this case, a change with time of the output signal due to deterioration of the light source 21 or contamination of the sample cell 20 can be corrected by comparison with the measured absorption characteristic of the reference light.
[0007]
FIG. 10 shows a single-light two-wavelength Fabry-Perot NDIR gas analyzer, which is adapted to the absorption characteristics of the gas to be measured by making the gap between two parallel mirrors (not shown) constituting the Fabry-Perot filter 26 variable. Two wavelengths, the wavelength and the wavelength of the reference light, are selected, and the selected infrared rays are detected by the infrared detector 23, respectively.
In this case, a change with time of the output signal due to deterioration of the light source 21 or contamination of the sample cell 20 can be corrected by comparison with the measured absorption characteristic of the reference light.
[0008]
FIG. 11 is a two-light one-wavelength NDIR gas analyzer, in which two light sources 21 and 27 are arranged so that the optical path lengths in the sample cell 20 are different, and the light is transmitted through a filter 22 that matches the absorption characteristics of the gas to be measured. Based on the ratio of the output signal of the infrared detector 23 detected in this way, the change over time of the output signal due to contamination of the sample cell 20 is corrected, and the concentration of the gas to be measured is measured.
[0009]
[Problems to be solved by the invention]
However, in such an NDIR gas analyzer, when the gas to be measured contains a plurality of components, the number of filters must be increased in order to measure the concentration of the plurality of components. However, there is a problem that the cost of the analyzer increases and the analyzer becomes large.
[0010]
The present invention has been made to solve the above-described problems. By realizing a Fabry-Perot filter that selectively transmits infrared light in three wavelength bands including reference light, two components of the gas to be measured are obtained. An object of the present invention is to provide an infrared gas analyzer capable of simultaneously measuring the concentration of water.
[0011]
[Means for Solving the Problems]
According to claim 1 of the present invention, a Fabry-Perot filter that selectively transmits infrared light from a light source in three wavelength bands including each wavelength band corresponding to the absorption characteristics of two components contained in the gas to be measured and reference light. The short wavelength λ1 at the peak of infrared absorption of one of the two components contained in the gas to be measured and the other component between the first mirror provided on the substrate and the first mirror. A gap is formed in the wavelength range of both peaks (λ1 to λ2) with the long wavelength λ2 at the infrared absorption peak, and the reference light is transmitted in an initial state, and an external force is applied to the first peak. A second mirror disposed displaceably facing one mirror, a first electrode provided on the first mirror, and a second electrode disposed on the second mirror and disposed opposite the first electrode. The second mirror is displaced by applying a potential difference between the first electrode and the second electrode, and the length of the gap is variable in three stages A to C below. It is a Fabry-Perot filter.
Corresponds to the absorption characteristics of the other components of the length C) the two components transmitted through the infrared wavelength band corresponding to the absorption characteristics of one component of the length B) the two components transmitted through A) said reference beam Length for transmitting infrared light in the selected wavelength band.
According to a second aspect of the present invention, in the Fabry-Perot filter according to the first aspect, the first mirror and the second mirror are made of silicon.
[0014]
According to a third aspect of the present invention, a light source for irradiating the gas to be measured with infrared light, a wavelength selection filter for selectively transmitting infrared light from the light source, and infrared detection for detecting infrared light transmitted through the wavelength selective filter An infrared gas analyzer that measures a concentration of the gas to be measured based on an output of the infrared detector, wherein the wavelength selection filter is a Fabry-Perot filter according to claim 1 or 2. It is an infrared gas analyzer characterized by comprising.
[0015]
According to a fourth aspect of the present invention, a light source that irradiates the gas to be measured with infrared light, a wavelength selection filter that selectively transmits infrared light from the light source, and infrared detection that detects infrared light transmitted through the wavelength selective filter. An infrared gas analyzer that measures a concentration of the gas to be measured based on an output of the infrared detector, wherein the wavelength selection filter is a Fabry-Perot filter according to claim 1 or 2. An infrared gas analyzer comprising a wide bandpass filter configured and disposed in an optical path preceding the infrared detector and transmitting only a wavelength in a specific band.
[0016]
In claim 5 of the present invention, the measurement gas contains two components of carbon dioxide and water vapor, the infrared gas analyzer of claim 3 or claim 4 wherein determining the concentration of the two components It is.
[0017]
In claim 6 of the present invention, the measurement gas contains two components of carbon dioxide and carbon monoxide, according to claim 3 or claim 4 infrared gas wherein measuring the concentration of the two components It is an analyzer.
[0018]
In claim 7 of the present invention, the measurement gas contains two components of nitrogen oxides and sulfur oxides, infrared claim 3 or claim 4 wherein determining the concentration of the two components It is a gas analyzer.
[0019]
In claim 8 of the present invention, the measurement gas contains two components of carbon dioxide and nitrogen oxides, according to claim 3 or claim 4 infrared gas wherein measuring the concentration of the two components It is an analyzer.
[0020]
In Claim 9 of this invention, the said to-be-measured gas contains two components of a carbon dioxide and a sulfur oxide, The density | concentration of these two components is measured, The infrared gas of Claim 3 or Claim 4 characterized by the above-mentioned. It is an analyzer.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
In the following drawings, the same parts as those in FIGS. 7 to 13 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.
FIG. 1 is a sectional view showing the configuration of an embodiment of the present invention.
[0022]
In the following, carbon dioxide having an infrared absorption wavelength peak of about 4.25 μm as shown in FIG. 2 and water vapor having an infrared absorption wavelength peak of about 2.7 μm as shown in FIG. A gas containing two components will be described as a gas to be measured.
[0023]
The Fabry-Perot filter is designed so that its center wavelength is in the wavelength range of 2700 nm (λ1) to 4250 nm (λ2), and the free spectral region FSR is larger than 4250-2700 nm (λ2-λ1) = 1550 nm. The
[0024]
The Fabry-Perot filter shown in FIG. 1 is designed with a free spectral region FSR = 2000 nm, a full width at half maximum HBW = 140 nm, a maximum transmittance Tmax = 80%, and a finesse finess = 14.
[0025]
In FIG. 1, a first mirror 3 is formed on a silicon substrate 1 via an oxide film 2, and a second mirror 4 is formed on an oxide film 5 formed on the first mirror 3. 3 are arranged opposite to each other.
[0026]
A gap h corresponding to the film thickness of the oxide film 5 is formed between the first mirror 3 and the second mirror 4 by etching the oxide film 5 from the etching hole 6 formed in the second mirror 4. The two mirrors 4 can be displaced in the direction of the first mirror 3 by applying an external force.
[0027]
The first mirror 3 and the second mirror 4 are made of, for example, polycrystalline silicon, and the surface of the first mirror 3 is doped with high-concentration impurities to form the first electrode 7. A second electrode 8 is formed by doping impurities of a concentration.
[0028]
Then, an external electrode 9 that allows the first electrode 7 to be energized from the outside is formed in contact with the first electrode 7, and an external electrode 10 that allows the second electrode 8 to be energized from the outside contacts the second electrode 8. Is formed.
[0029]
In this case, the center wavelength λ of the Fabry-Perot filter corresponds to the length of the gap h, that is, the thickness of the oxide film 5, and is 3100 nm, for example.
And since the 1st mirror 3 becomes a lower mirror of a Fabry-Perot filter, the optical film thickness needs to be set to λ / 4. In this case, the film thickness of the oxide film is 592 nm (refractive index: 1.309), The film thickness of the first mirror 3 and the second mirror 4 is 248 nm (refractive index 3.125).
[0030]
Next, the operation will be described.
FIGS. 4A, 4B, and 4C are operation explanatory diagrams of the Fabry-Perot filter shown in FIG.
[0031]
When a potential difference is applied to the first electrode 7 and the second electrode 8 via the external electrode 9 and the external electrode 10, an electrostatic attractive force is generated between the first electrode 7 and the second electrode 8, and the second mirror 4 is displaced in the direction of the first mirror 3, and the length of the gap h changes.
By changing this voltage, it is possible to obtain the length of the gap that transmits infrared rays in the wavelength band corresponding to the absorption characteristics of the gas to be measured.
[0032]
For example, in FIG. 4A, when the gap h in the initial state where no voltage is applied (that is, the film thickness of the insulating layer is about 3100 nm) is set as the reference light measurement state, It can be used as correction data for contamination of the optical system.
[0033]
Then, as shown in FIG. 4B, when the potential difference is adjusted so that the gap h is about 2590 nm, water vapor can be measured, and as shown in FIG. When the potential difference is adjusted to be about 2270 nm, carbon dioxide can be measured.
[0034]
As described above, since the length of the gap h is variable in three stages, it is possible to realize a Fabry-Perot filter that selectively transmits infrared light in three wavelength bands including reference light.
[0035]
A light source for irradiating the gas to be measured with infrared light; a wavelength selection filter for selectively transmitting infrared light from the light source; and an infrared detector for detecting infrared light transmitted through the wavelength selective filter. In the infrared gas analyzer that measures the concentration of the gas to be measured based on the output of the detector, when the Fabry-Perot filter as described above is used, the two components of the gas to be measured can be obtained without increasing the number of wavelength selection filters. Since the concentration can be measured simultaneously, the infrared gas analyzer can be reduced in size and cost.
[0036]
By the way, the Fabry-Perot filter exhibits a plurality of transmission peaks in a plurality of wavelength bands for one gas, as shown in FIG.
For example, in the case of carbon dioxide with a gap h of 2270 nm, in the case of water vapor with a gap of about 2250 nm and around 4250 nm, in the case of water vapor with a gap of 2590 nm, in the case of reference light with a gap of 3100 nm, around 3100 nm and 2200 nm. There is a peak in the vicinity.
[0037]
Therefore, as shown in FIG. 6, by providing a wide bandpass filter 12 that transmits wavelengths from 2600 nm to 4500 nm, for example, and does not transmit other bands in the optical path preceding the infrared detector 14. As shown in FIG. 5, in the case of carbon dioxide with a gap h of 2270 nm, only in the vicinity of 4250 nm, in the case of water vapor with a gap h of 2590 nm, only in the vicinity of 2700 nm, and in the case of reference light with a gap of 3100 nm, only in the vicinity of 3100 nm By selecting only one peak in each gap, the amount of absorption of a plurality of gases can be measured.
[0038]
In FIG. 6, the wide bandpass filter 12 is provided in the optical path between the light source 11 and the Fabry-Perot filter 13, but the wide bandpass filter 12 is provided in the optical path between the Fabry-Perot filter 13 and the infrared detector 14. It may be provided.
[0039]
In this embodiment, the case where two components of carbon dioxide and water vapor are measured has been described. However, the center wavelength of the Fabry-Perot filter is the infrared absorption peak of two components at λ1 (short wavelength) and λ2 (long wavelength). Then, the wavelength range is λ1 to λ2, and the free spectral range may be designed to be larger than λ2 to λ1, so for example, two components of carbon dioxide and carbon monoxide, two components of nitrogen oxide and sulfur oxide. It is possible to measure the concentration by a combination of.
[0040]
【The invention's effect】
As described above, according to the first to third aspects of the present invention, since the gap length is variable in three stages, infrared rays in three wavelength bands including the reference light are selectively transmitted. A Fabry-Perot filter can be realized.
[0041]
According to claim 4 of the present invention, since the Fabry-Perot filter according to claims 1 to 3 of the present invention is used, the concentrations of the two components of the gas to be measured can be simultaneously increased without increasing the number of wavelength selection filters. Measurement can be performed, and the infrared gas analyzer can be reduced in size and cost.
[0042]
According to Claim 5 of the present invention, since the Fabry-Perot filter according to Claims 1 to 3 of the present invention is used and a wide bandpass filter that transmits infrared light of only a specific bandwidth is provided, An infrared gas analyzer capable of selecting only one peak and measuring a plurality of gas concentrations can be provided.
[0043]
According to claim 6 of the present invention, an infrared gas analyzer capable of measuring two components of carbon dioxide and water vapor can be provided.
[0044]
According to claim 7 of the present invention, an infrared gas analyzer capable of measuring two components of carbon dioxide and carbon monoxide can be provided.
[0045]
According to claim 8 of the present invention, an infrared gas analyzer capable of measuring two components of nitrogen oxide and sulfur oxide can be provided.
[0046]
According to claim 9 of the present invention, an infrared gas analyzer capable of measuring two components of carbon dioxide and nitrogen oxide can be provided.
[0047]
According to claim 10 of the present invention, an infrared gas analyzer capable of measuring two components of carbon dioxide and sulfur oxide can be provided.
[0048]
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of an embodiment of the present invention.
FIG. 2 is an infrared absorption characteristic diagram of carbon dioxide.
FIG. 3 is an infrared absorption characteristic diagram of water vapor.
FIG. 4 is an operation explanatory diagram of the embodiment of the present invention.
FIG. 5 is a transmission characteristic and gas absorption characteristic diagram of a Fabry-Perot filter.
FIG. 6 is a schematic configuration diagram of an infrared gas analyzer using an embodiment of the present invention.
FIG. 7 is a configuration diagram of a conventional NDIR gas analyzer.
FIG. 8 is a configuration diagram of a conventional NDIR gas analyzer.
FIG. 9 is a configuration diagram of a conventional NDIR gas analyzer.
FIG. 10 is a configuration diagram of a conventional NDIR gas analyzer.
FIG. 11 is a configuration diagram of a conventional NDIR gas analyzer.
FIG. 12 is a graph showing infrared transmission characteristics and absorption characteristics of a filter.
FIG. 13 is a graph showing infrared transmission characteristics and absorption characteristics of a filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 3 First mirror 4 Second mirror 7 First electrode 8 Second electrode 11 Light source 12 Wide band pass filter 13 Fabry-Perot filter 14 Infrared detector h Gap

Claims (9)

In a Fabry-Perot filter that selectively transmits infrared light from a light source in each wavelength band corresponding to absorption characteristics of two components contained in a gas to be measured and three wavelength bands including reference light,
A first mirror provided on the substrate;
Between this first mirror, both peaks of the short wavelength λ1 at the infrared absorption peak of one of the two components contained in the gas to be measured and the long wavelength λ2 at the infrared absorption peak of the other component In the initial state, a gap having a length that allows the reference light to pass therethrough is formed, and an external force is applied to displace the first mirror so as to be displaceable. A second mirror,
A first electrode provided on the first mirror;
A second electrode provided on the second mirror and disposed opposite to the first electrode;
A Fabry-Perot characterized in that the second mirror is displaced by applying a potential difference between the first electrode and the second electrode, and the length of the gap is variable in three stages A to C below. filter.
Corresponds to the absorption characteristics of the other components of the length C) the two components transmitted through the infrared wavelength band corresponding to the absorption characteristics of one component of the length B) the two components transmitted through A) said reference beam Length to transmit infrared in the specified wavelength band   The Fabry-Perot filter according to claim 1, wherein the first mirror and the second mirror are made of silicon. A light source for irradiating the gas to be measured with infrared light; a wavelength selection filter for selectively transmitting infrared light from the light source; and an infrared detector for detecting infrared light transmitted through the wavelength selective filter. In an infrared gas analyzer that measures the concentration of the gas to be measured based on the output of the vessel,
3. The infrared gas analyzer according to claim 1, wherein the wavelength selective filter includes the Fabry-Perot filter according to claim 1 or 2. A light source for irradiating the gas to be measured with infrared light; a wavelength selection filter for selectively transmitting infrared light from the light source; and an infrared detector for detecting infrared light transmitted through the wavelength selective filter. In an infrared gas analyzer that measures the concentration of the gas to be measured based on the output of the vessel,
The wavelength selective filter includes the Fabry-Perot filter according to claim 1 or claim 2,
An infrared gas analyzer comprising a wide bandpass filter disposed in an optical path preceding the infrared detector and transmitting only a wavelength in a specific band. The infrared gas analyzer according to claim 3 or 4, wherein the gas to be measured includes two components of carbon dioxide and water vapor, and the concentration of the two components is measured. The infrared gas analyzer according to claim 3 or 4, wherein the gas to be measured includes two components, carbon dioxide and carbon monoxide, and the concentration of the two components is measured. 5. The infrared gas analyzer according to claim 3, wherein the gas to be measured includes two components of nitrogen oxide and sulfur oxide, and the concentration of the two components is measured. The infrared gas analyzer according to claim 3 or 4, wherein the gas to be measured includes two components of carbon dioxide and nitrogen oxide, and the concentration of the two components is measured. The infrared gas analyzer according to claim 3 or 4, wherein the gas to be measured includes two components of carbon dioxide and sulfur oxide, and the concentration of the two components is measured.

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