JP2009074833A - Gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct an influence of output fluctuation of a semiconductor laser or the like without providing an optical waveguide for reference light by branching an optical waveguide. <P>SOLUTION: In this gas sensor equipped with an optical waveguide layer, and a reaction film 12 provided on the optical waveguide layer, to be reacted with gas to be detected, laser light including a P-polarized component and an S-polarized component is allowed to enter the optical waveguide layer, and guided light emitted from the optical waveguide layer is split into the P-polarized component and the S-polarized component by a polarization beam splitter 8, and the P-polarized component wherein the guided light is hardly attenuated by the gas to be detected is detected as reference light by the first photodiode 6-1, and simultaneously the S-polarized component attenuated corresponding to the concentration of the gas to be detected is detected by the second photodiode 6-2, and the concentration of the gas to be detected wherein an influence of output fluctuation of the semiconductor laser 5 or the like is corrected is determined from outputs from both photodiodes 6-1, 6-2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a gas sensor, and more particularly to a gas sensor using an optical waveguide in which a detection material that reacts with a gas to be detected is formed on the surface of an optical waveguide layer.

  As this type of gas sensor, for example, there is a gas sensor disclosed in Patent Document 1.

  FIG. 7 is a diagram showing a schematic configuration of the gas sensor disclosed in Patent Document 1. As shown in FIG.

  In the figure, an optical waveguide 31 is provided on a substrate 30, and a detection material 32 that reacts with a gas to be detected and changes color is provided thereon. The monitor light 34 is incident in parallel to the optical waveguide 31 from a light source 33 such as a laser, the amount of exit light 35 exiting the optical waveguide 31 is measured by the optical detector 36, and the light guided to the optical waveguide 31 is attenuated. Thus, the concentration of the gas to be detected is detected.

  In general, the output of the semiconductor laser as the light source 33 is likely to fluctuate depending on the ambient temperature, humidity, and the like, and this output fluctuation has a drawback in that the detection accuracy by the optical detector 36 is affected.

For this reason, the optical waveguide into which the laser light is incident is branched into two, and one optical waveguide is provided with a detection material that reacts with the gas to be detected to provide an optical waveguide for gas detection, and the other optical waveguide is The optical waveguide for reference light without the detection material is used, and the amount of light from the optical waveguide for gas detection is compared with the amount of reference light from the optical waveguide for reference light. There is one that detects the concentration of the gas to be detected (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 7-243973 Japanese Patent Publication No. 4-81738

  In the above-mentioned Patent Document 2, it is possible to correct the output fluctuation of the laser light source using the reference light, but it is necessary to branch the optical waveguide to provide an optical waveguide for reference light, and there is a problem that the configuration becomes complicated. .

  The present invention has been made in view of the above-described points, and an object of the present invention is to make it possible to correct an influence such as output fluctuation of a semiconductor laser without branching an optical waveguide.

  The gas sensor according to the present invention is a gas sensor including an optical waveguide layer and a detection material that is provided on the optical waveguide layer and reacts with a gas to be detected. The gas sensor includes a laser beam including a P-polarized component and an S-polarized component. The guided light emitted from the optical waveguide layer is separated into a P-polarized component and an S-polarized component, and each polarized component is detected to determine the concentration of the detected gas.

  The optical waveguide layer is preferably formed on a transparent substrate.

  The vibration direction of the electric vector of the S-polarized component contained in the laser light is preferably parallel to the surface of the optical waveguide layer.

  The S-polarized component contained in the laser light attenuates the guided light according to the concentration of the gas to be detected, for example, ammonia gas, whereas the guided light of the P-polarized component hardly attenuates, and the attenuation is , Small enough to be negligible compared to the S-polarized component.

According to the gas sensor of the present invention, laser light containing a P-polarized component and an S-polarized component is incident on the optical waveguide layer, and the guided light emitted from the optical waveguide layer is separated into a P-polarized component and an S-polarized component, The semiconductor, which is a laser light source, can measure the concentration of the gas to be detected based on the S-polarized light component that attenuates in accordance with the concentration of the gas to be detected, and uses the P-polarized light component that is hardly attenuated by the gas to be detected as reference light. Effects such as laser output fluctuations can be corrected.
In one embodiment of the present invention, a laser light source that outputs laser light, a separating unit that separates the guided light emitted from the optical waveguide layer into a P-polarized component and an S-polarized component, and the separated P-polarized light A first photoelectric conversion element for detecting the component and a second photoelectric conversion element for detecting the separated S-polarized component are provided.

  According to this embodiment, the concentration of the gas to be detected can be obtained based on the output of the second photoelectric conversion element that detects the S-polarized light component that attenuates in accordance with the concentration of the gas to be detected. Based on the output of the first photoelectric conversion element that detects the P-polarized light component that hardly attenuates, the influence of the output fluctuation of the laser light source can be canceled.

  In a preferred embodiment of the present invention, the outputs of the first and second photoelectric conversion elements when the gas to be detected is not present are P1 and S1, and the first and first when the gas to be detected is present. When the output of the photoelectric conversion element 2 is P2 and S2, the concentration of the detected gas when the detected gas exists is a value proportional to (S1 / S2) × (P2 / P1). It is what you want.

  The output of each photoelectric conversion element corresponds to the intensity of each polarization component.

  According to this embodiment, using the outputs P1 and S1 of the photoelectric conversion elements in the initial state where the gas to be detected does not exist and the outputs P2 and S2 of the photoelectric conversion elements when the gas to be detected exists, S polarization Obtaining the concentration of the gas to be detected corrected for the influence of the output fluctuation of the laser light source, etc., from the rate of change in output for the component (S1 / S2) and the rate of change in output for the P-polarized component (P1 / P2) Can do.

  In another embodiment of the present invention, a semiconductor laser that outputs a randomly polarized laser beam including an S-polarized component and a P-polarized component may be used as the laser light source.

  In still another embodiment of the present invention, a semiconductor laser that outputs linearly polarized laser light by using a retardation plate that converts linearly polarized light into circularly polarized light or elliptically polarized light may be used as the laser light source.

  According to the present invention, the concentration of the gas to be detected can be measured based on the S-polarized light component in which the guided light attenuates according to the concentration of the gas to be detected, and the P-polarized light component in which the guided light is hardly attenuated by the gas to be detected. By using the reference light, it is possible to correct the influence of fluctuations in the output of the semiconductor laser, which is a laser light source. Thus, unlike the conventional example, it is not necessary to branch the optical waveguide to provide an optical waveguide for reference light, and the configuration is simplified.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic configuration diagram of a gas sensor according to an embodiment of the present invention.

The gas sensor 1 of this embodiment measures the concentration of ammonia (NH ₃ ) gas that is a gas to be detected.

  This gas sensor 1 has a sensor chip part 2 as a gas detection part for detecting a gas to be detected.

  As shown in the enlarged view of FIG. 2, the sensor chip unit 2 includes an optical waveguide layer 11 formed on the glass substrate 10, and a reaction film as a detection material that reacts with ammonia gas on the optical waveguide layer 11. 12 is formed into an optical waveguide. This reaction film 12 is made of a material that reacts with ammonia gas and shifts its absorption spectrum, and the guided light is attenuated depending on the concentration of ammonia gas.

  The reaction membrane 12 is reversible, can be regenerated with air that does not contain nitrogen gas or ammonia gas, and can repeatedly measure the concentration of ammonia gas.

  On the glass substrate 10, right-angle prisms 13 and 14 for guiding light to the optical waveguide layer 11 and for extracting light are respectively provided. The waveguide light repeats total reflection as shown in FIG. In the meantime, evanescent waves ooze out on the surface of the optical waveguide layer.

  Since the sensor chip unit 2 has a different degree of color change of the reaction film 12 depending on the gas concentration of ammonia gas, the absorption rate of the evanescent wave changes and the output of light guided to the optical waveguide layer 11 becomes weak. . Therefore, the concentration of ammonia gas can be detected by measuring the output intensity of the guided light.

  In the gas sensor of this embodiment, the S-polarized component of the laser light incident on the optical waveguide layer 11 is attenuated in accordance with the concentration of ammonia gas and the output intensity of the guided light is weakened as described above. The P-polarized component is such that the attenuation of the guided light is negligibly small and the output intensity of the guided light hardly changes depending on the concentration of ammonia gas, and the P-polarized component is used as the reference light.

  For this reason, as shown in FIG. 1, the gas sensor 1 of this embodiment converts the laser light output as linearly polarized light from the laser diode 5 into circularly polarized light by the phase difference plate 4, and passes through the right-angle prism 13. The light is incident on the optical waveguide layer 11, and the guided light from the optical waveguide layer 11 is taken out via the right-angle prism 14, and is separated into a P-polarized component and an S-polarized component by the polarization beam splitter 8, and Detected by the first and second photodiodes 6-1 and 6-2, and based on the outputs of both photodiodes 6-1 and 6-2, the calculating means 7 calculates the ammonia gas concentration. .

  FIG. 3 shows changes in the outputs of the first and second photodiodes 6-1 and 6-2 that detect the P-polarized light component and the S-polarized light component, respectively.

  In the figure, the alternate long and short dash line indicates the change in the output of the first photodiode 6-1 that detects the P-polarized component, and the solid line indicates the change in the output of the second photodiode 6-2 that detects the S-polarized component. The change is shown when ammonia gas is introduced from the initial state where no ammonia gas exists, and then nitrogen gas for regenerating the reaction film 12 of the sensor chip unit 2 is introduced instead of ammonia gas.

  In the initial state where no ammonia gas exists, the P-polarized component and the S-polarized component are hardly attenuated, and the outputs of the photodiodes 6-1 and 6-2 that detect the polarized components at this time are output. , P1, S1.

  Next, when ammonia gas is introduced and reacted with the sensor chip unit 2, the S-polarized component is greatly attenuated according to the concentration of the ammonia gas, whereas the P-polarized component is hardly attenuated. The intensity of the output signal of each photodiode 6-1 and 6-2 that detects each polarization component at this time is P2 and S2.

  Then, by stopping the introduction of ammonia gas and introducing nitrogen gas, the reaction film 12 of the sensor chip unit 2 is regenerated, and the output of the attenuated S-polarized component is restored.

  In this embodiment, the change in the output of the second photodiode 6-2 that detects the s-polarized light component that attenuates in accordance with the concentration of ammonia gas, and the first photodiode that detects the P-polarized light component as reference light. Correction is performed by changing the output of 6-1.

  That is, the output S1 of the second photodiode 6-2 that detects the S-polarized component in the initial state in which no ammonia gas is present, and the second photodiode 6-2 that detects the S-polarized component in the presence of ammonia gas. The value S1 / S2 divided by the output S2 of the first output is the output P1 of the first photodiode 6-1 that detects the P-polarized component in the initial state where no ammonia gas is present, and the P-polarized component when the ammonia gas is present. Dividing by the value P1 / P2 divided by the output P2 of the first photodiode 6-1 to be detected is (S1 / S2) ÷ (P1 / P2) = (S1 / S2) × (P2 / P1).

  The output ratio S1 / S2 of the S-polarized component includes not only attenuation according to the ammonia gas concentration but also the influence of fluctuations in the laser beam, etc., while the output ratio P1 / P2 of the P-polarized component is It does not depend on the concentration of ammonia gas, and includes the effects of fluctuations in laser light. In addition, both the S-polarized component and the P-polarized component change at the same rate due to variations in laser light other than the concentration of ammonia gas.

  Therefore, by dividing the output ratio S1 / S2 of the S-polarized component by the output ratio P1 / P2 of the P-polarized component, it is possible to correct the influence due to the fluctuation of the laser beam or the like.

  Hereinafter, specific examples of the present invention will be described.

  The sensor chip part 2 of the present example was manufactured as follows.

  (1) A soda lime glass ultrasonically cleaned with 1% ammonia water is immersed in potassium nitrate melted at 400 ° C. for 100 minutes, and sodium ions and potassium ions on the surface layer are exchanged to form an optical waveguide layer rich in potassium ions. Formed. Whereas the refractive index of the substrate is 1.512, the refractive index of the ion-exchanged optical waveguide layer is 1.518.

  (2) On the optical waveguide layer, BTB (bromothymol blue), which is a pH indicator, was formed as a reaction film that changes color by reacting with ammonia gas by a vacuum vapor deposition machine. With respect to a glass substrate having a size of 13 mm × 53 mm and a thickness of 1 mm, the size was 13 mm × 15 mm and a thickness of about 100 nm in the middle of the substrate.

  (3) A prism was closely attached with a matching oil on a substrate provided with a reaction film on the waveguide layer to form a sensor chip portion.

The sensor chip portion obtained as described above was housed and disposed in a chamber having an inlet for ammonia gas and nitrogen gas for regeneration and a gas outlet.
Next, the concentration of ammonia gas was measured by the following procedure.

  (1) Laser light from a 635 nm semiconductor laser was incident on the optical waveguide layer of the sensor chip portion as circularly polarized light through a phase difference plate. In order to use the “0th-order mode”, the incidence angle was 65 °.

  (2) The light emitted from the optical waveguide layer was separated into an S-polarized component and a P-polarized component using a polarization beam splitter, and each was detected by a photoelectric conversion element.

  (3) The sensor chip part was fixed so that the gas hits the reaction film of the sensor chip part, and ammonia gas diluted to a desired concentration was led to the reaction film. Ammonia gas was sucked at 500 ml / min by a pump from the discharge port side.

  (4) A standard ammonia gas of 300 ppb, 500 ppb, and 800 ppb was prepared and reacted sequentially with one sensor chip portion.

  The result is shown in FIG. In FIG. 4, the horizontal axis represents the elapsed time, and the vertical axis represents the outputs (%) of the first and second photodiodes that detect the P-polarized component and the S-polarized component, respectively.

  In FIG. 4, as described above, 300 ppb of ammonia standard gas is introduced to react with the sensor chip part, and instead of this ammonia standard gas, nitrogen gas is introduced to regenerate the sensor chip part, Instead of nitrogen gas, 500 ppb ammonia standard gas is introduced to react with the sensor chip part, and instead of ammonia standard gas, nitrogen gas is introduced to regenerate the sensor chip part. Further, instead of nitrogen gas, A change is shown when 800 ppb ammonia standard gas is introduced and reacted with the sensor chip portion, and nitrogen gas is introduced instead of the ammonia standard gas.

  As shown in FIG. 4, the S-polarized component indicated by the solid line is greatly attenuated according to the respective concentrations of the 300 ppb, 500 ppb, and 800 ppb ammonia standard gases as compared to the P-polarized component indicated by the alternate long and short dash line. I understand that.

  In addition, although attenuation | damping is recognized also about P polarization | polarized-light component, it is thought that this is based on the influence of the S polarization | polarized-light component which the S polarization component was not isolate | separated completely.

  (5) Based on the obtained results, FIG. 5 shows the results of plotting the ammonia gas concentration on the horizontal axis and the correction value (S1 / S2) × (P2 / P1) of the output on the vertical axis.

As shown in FIG. 5, a proportional relationship is recognized between the output correction value (S1 / S2) × (P2 / P1) and the ammonia gas concentration, and the proportionality constant can be obtained from FIG.
Therefore, the unknown concentration obtained by correcting the influence of the fluctuation of the laser beam or the like from the correction value (S1 / S2) × (P2 / P1) of the output obtained by measuring the ammonia gas having an unknown concentration and the proportionality constant. It is possible to calculate the concentration of ammonia gas.

(Embodiment 2)
In the above embodiment, as shown in FIG. 1, a linearly polarized laser diode 5 is used, and linearly polarized light from the laser diode 5 is converted into circularly polarized light by the phase difference plate 4. As another embodiment, as shown in FIG. 6, a laser diode 5-1 having a random polarization output may be used, and the phase difference plate may be omitted.

  Other configurations are the same as those of the above-described embodiment.

  In each of the above-described embodiments, description has been made by applying to the measurement of the concentration of ammonia gas. However, the present invention can also be applied to measurement of gases other than ammonia gas if the detection material is changed to one corresponding to the gas to be detected. Of course.

It is a schematic block diagram of the gas sensor which concerns on embodiment of this invention. It is a block diagram of the sensor chip part of FIG. It is a figure for demonstrating the output change of each photodiode which each detects an S polarization component and a P polarization component. It is a figure which shows the output change of each photodiode when measuring 300ppb, 500ppb, and 800ppb ammonia standard gas. It is a figure which shows the relationship between the calculated value based on the output change of each photodiode, and ammonia gas concentration. It is a schematic block diagram of the gas sensor which concerns on other embodiment of this invention. It is a figure which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Sensor chip part 4 Phase difference plate 5,5-1 Laser diode 8 Polarization beam splitter 10 Glass substrate 11 Optical waveguide layer 12 Reaction film

Claims (5)

A gas sensor including an optical waveguide layer and a detection material that is provided on the optical waveguide layer and reacts with a detection target gas,
Laser light including a P-polarized component and an S-polarized component is incident on the optical waveguide layer, and the guided light emitted from the optical waveguide layer is separated into a P-polarized component and an S-polarized component. A gas sensor, wherein the concentration is detected and the concentration of the detected gas is determined.   A laser light source that outputs laser light; a separating unit that separates the guided light emitted from the optical waveguide layer into a P-polarized component and an S-polarized component; and a first photoelectric conversion that detects the separated P-polarized component. The gas sensor according to claim 1, comprising: an element; and a second photoelectric conversion element that detects the separated S-polarized light component.   The outputs of the first and second photoelectric conversion elements when the gas to be detected does not exist are P1 and S1, and the outputs of the first and second photoelectric conversion elements when the gas to be detected exists. 3. The gas sensor according to claim 2, wherein the concentration of the gas to be detected when the gas to be detected is present as a value proportional to (S1 / S2) × (P2 / P1) when P2 and S2 are set. .   The gas sensor according to claim 2 or 3, wherein the laser light source is a semiconductor laser, and a polarization state of an output of the semiconductor laser is random. The laser light source is a semiconductor laser, and the polarization state of the output of the semiconductor laser is linearly polarized light,
The gas sensor according to claim 2, further comprising a retardation plate that converts the linearly polarized light into circularly polarized light or elliptically polarized light and makes the light incident on the optical waveguide layer.

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