JP5660545B2 - Optical gas sensor - Google Patents

Description

  The present invention relates to an optical gas sensor. More specifically, the present invention relates to an optical gas sensor using a Raman scattering method or an absorption measurement method.

  As a gas sensor, a contact-type gas sensor such as a contact combustion type or a semiconductor type and an optical non-contact type gas sensor are known.

Of these, contact-type gas sensors are widely used because they are small, light, and inexpensive. However, the contact type gas sensor has the following problems.
(1) The response speed is slow The contact-type gas sensor measures the gas concentration by directly contacting the measurement target gas with the detection unit and measuring changes in electrical resistance, current, and the like. Therefore, in order to measure an accurate gas concentration, it takes several tens of seconds until the electric resistance value and current value are stabilized, and there is a problem that the response speed is slow.
(2) One type of gas measurement per sensor The contact-type gas sensor can measure only one type of gas per sensor. Therefore, in order to measure a plurality of types of gases, it is necessary to prepare a plurality of sensors for each type of gas to be measured.
(3) Many false alarming factors Since the contact-type gas sensor measures the gas concentration using a reaction catalyst or heat generation, there is a possibility that interference with gases other than the measurement target may occur, which may cause false alarms. In addition, since the gas to be measured cannot be detected unless it contacts the detector, depending on the wind direction and installation position, the contact time until the electrical resistance value and current value become stable is insufficient, which may cause false alarms. is there.
(4) Risk of ignition and explosion of combustible gas Contact type gas sensors measure the gas to be measured directly in contact with the detection unit. Therefore, if combustible gas comes in contact with electrical systems such as electrodes and electric wires, it will ignite or explode. There is a fear. Moreover, when the portable gas sensor detects the measurement target gas, it is already in a state of exposing itself to danger.

  On the other hand, since the non-contact optical gas sensor uses a Raman scattering method or an absorption measurement method, in principle, the response speed is fast, and a plurality of sensors can be used with one sensor by analyzing the spectrum of the Raman scattered light and the light absorption spectrum. It has the advantage that it can measure various types of gases, has few false alarms, and does not need to be equipped with an electric system in the detection section, so there is no risk of ignition or explosion by combustible gas.

  However, conventional optical gas sensors are large and expensive because optical parts such as mirrors and lenses are large and an adjustment mechanism is required to adjust the optical system according to the measurement conditions such as environmental temperature. (For example, Patent Document 1, Patent Document 2, Non-Patent Document 1).

JP 2011-158307 A JP 2001-188040 A

Tetsuo Fukuchi and Hideki Ninomiya “Ultraviolet Absorption Spectroscopic Measurements of Trace NH3 in Gas Containing High Concentration SO2” IEICE Journal A 2011 Vol.131 No.7 pp.540-546

  In view of the above circumstances, an object of the present invention is to provide a small and inexpensive optical gas sensor.

An optical gas sensor according to a first aspect of the present invention includes an incident side optical fiber having one end connected to a light source, a light receiving side optical fiber having one end connected to a photodetector, and light emitted from the other end of the incident side optical fiber. And a gas detection unit configured with an optical system that makes light emitted by interaction with the measurement target gas incident on the other end of the light receiving side optical fiber. The unit includes a small optical bench, and the small optical bench includes an incident side optical fiber fixing unit that fixes the other end of the incident side optical fiber, and a light receiving side optical fiber that fixes the other end of the light receiving side optical fiber. A fixed portion and a light reflector that reflects light are integrally formed, and the gas detection portion includes the incident-side optical fiber that enters light into the measurement target gas, and the light from the incident-side optical fiber. Arranged on the axis, and Said light reflector that reflects light emitted from the bar at an angle which is not directly incident on the light receiving side optical fiber, the forward emitted by interaction with the measurement target gas with light emitted from the incident-side optical fiber The light receiving side light arranged at a position where the Raman scattered light and the backward Raman scattered light emitted by the interaction between the light reflected by the light reflector and the gas to be measured enter without passing through the reflection. A Raman scattering optical system is constituted by the fiber.
An optical gas sensor according to a second aspect of the present invention includes an incident side optical fiber having one end connected to a light source, a light receiving side optical fiber having one end connected to a photodetector, and light emitted from the other end of the incident side optical fiber. And a gas detection unit configured with an optical system that makes light emitted by interaction with the measurement target gas incident on the other end of the light receiving side optical fiber. The unit includes a small optical bench, and the small optical bench includes an incident side optical fiber fixing unit that fixes the other end of the incident side optical fiber, and a light receiving side optical fiber that fixes the other end of the light receiving side optical fiber. A fixed portion and a light reflector that reflects light are integrally formed, and the gas detection portion includes the incident-side optical fiber that enters light into the measurement target gas, and the light from the incident-side optical fiber. Arranged on the axis, and Said light reflector that reflects light emitted from the bar at an angle which is not directly incident on the light receiving side optical fiber, backward emitted by interaction with the measurement target gas with light emitted from the incident-side optical fiber The light receiving side light arranged at a position where the Raman scattered light and the forward Raman scattered light emitted by the interaction between the light reflected by the light reflector and the measurement target gas enter without passing through the reflection. A Raman scattering optical system is constituted by the fiber.
An optical gas sensor according to a third aspect of the invention includes an incident side optical fiber having one end connected to a light source, a light receiving side optical fiber having one end connected to a photodetector, and light emitted from the other end of the incident side optical fiber. And a gas detection unit configured with an optical system that makes light emitted by interaction with the measurement target gas incident on the other end of the light receiving side optical fiber. The unit includes a small optical bench, and the small optical bench includes an incident side optical fiber fixing unit that fixes the other end of the incident side optical fiber, and a light receiving side optical fiber that fixes the other end of the light receiving side optical fiber. A fixed portion and a light reflector that reflects light are integrally formed, and the gas detection portion includes the incident-side optical fiber that enters light into the measurement target gas, and the light from the incident-side optical fiber. Arranged at predetermined intervals across the shaft The pair of light reflectors that reflect forward Raman scattered light emitted by the interaction between the light emitted from the incident side optical fiber and the measurement target gas, and the pair of light reflectors are reflected. A Raman scattering optical system is constituted by the light receiving side optical fiber disposed at a position where forward Raman scattered light is incident .
An optical gas sensor according to a fourth aspect of the present invention is the optical gas sensor according to the first, second, or third aspect , wherein the small optical bench is formed by any one of photolithography, photofabrication, nanoimprint, injection molding, and mold molding. It is characterized by that.

According to the first invention, the following effects can be obtained.
a) Since the incident side optical fiber fixing part and the light receiving side optical fiber fixing part are integrally formed on the small optical bench, the incident side optical fiber is used as the incident side optical fiber fixing part, and the light receiving side optical fiber is used as the light receiving side optical fiber. The optical system can be configured without adjustment by simply fixing each to the fixing portion. Therefore, an adjustment mechanism for the optical system is unnecessary, and the gas detection unit can be downsized.
b) Since the light reflector is integrally formed on the small optical bench, the optical system can be configured without adjustment. Therefore, an adjustment mechanism for the optical system is unnecessary, and the gas detection unit can be downsized.
c) Since a Raman scattering optical system is configured in the gas detector, the measurement target gas can be measured by the Raman scattering method. Therefore, the response speed is fast, and a plurality of types of gases can be measured with one sensor by analyzing the spectrum of the Raman scattered light, there are few false alarm factors, and there is no fear of ignition or explosion due to combustible gas.
d) Since the forward Raman scattered light and the backward Raman scattered light are incident on the light receiving side optical fiber, the light intensity is increased, and the measurement target gas can be measured with high sensitivity.
According to the second aspect of the invention, since the forward Raman scattered light and the backward Raman scattered light are incident on the light receiving side optical fiber, the light intensity is increased, and the measurement target gas can be measured with high sensitivity.
According to the third aspect of the invention, since the forward Raman scattered light emitted to both sides of the optical fiber of the incident side optical fiber is incident on the light receiving side optical fiber, the light intensity is increased, and the measurement object is highly sensitive. Gas can be measured. In addition, since the light emitted from the incident side optical fiber is transmitted between the pair of light reflectors and does not enter the light receiving side optical fiber, the disturbance component is reduced and the measurement accuracy is improved .
According to the fourth invention, the incident side optical fiber fixing portion, the light receiving side optical fiber fixing portion, the optical component fixing portion and / or the optical component can be formed with high positional accuracy and dimensional accuracy. In addition, since the small optical bench can be formed in several mm to several tens mm square, a small gas detection unit can be manufactured. Moreover, since a small optical bench can be mass-produced, an optical gas sensor can be manufactured at low cost.

It is a top view of the gas detection part of the optical gas sensor which concerns on 1st Embodiment of this invention. It is an optical path figure of the gas detection part. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3. FIG. 5 is a cross-sectional view taken along line VV in FIG. 3. FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 1. It is a top view of the gas detection part of the optical gas sensor which concerns on 2nd Embodiment of this invention. It is a top view of the gas detection part of the optical gas sensor which concerns on 3rd Embodiment of this invention. It is a top view of the gas detection part of the optical gas sensor which concerns on 4th Embodiment of this invention. It is a top view of the gas detection part of the optical gas sensor which concerns on 5th Embodiment of this invention. It is a graph which shows the result of a light intensity test. It is a graph which shows the result of a sensitivity test.

Next, an embodiment of the present invention will be described with reference to the drawings.
(First embodiment)
The optical gas sensor 1 according to the first embodiment of the present invention is an optical gas sensor using a Raman scattering method. As shown in FIG. 1, the optical gas sensor 1 includes a gas detection unit 10, and an incident side optical fiber 20 and a light reception side optical fiber 30 connected to the gas detection unit 10.

  One end of the incident-side optical fiber 20 is connected to a light source such as a laser that is a monochromatic light source or a high-brightness LED, and guides light from the light source to the gas detection unit 10. One end of the light receiving side optical fiber 30 is connected to a photodetector such as a photomultiplier tube, an avalanche photodiode, a phototransistor, or a CCD, and the Raman scattered light generated by the gas detector 10 is transmitted to the photodetector. Guided. Note that an ADC (analog-digital conversion circuit), a computer, and the like are connected to the photodetector. And the kind and density | concentration of the gas which exist in the gas detection part 10 are computable from the detection signal of a photodetector with a well-known method. For example, the concentration of the measurement target gas can be measured by inserting an interference filter between the light receiving side optical fiber 30 and the photodetector and selecting the Raman scattered light corresponding to the measurement target gas by the interference filter. Further, the type of gas present in the gas detection unit 10 can be specified by exchanging the interference filter.

  The gas detection unit 10 is a part that is directly exposed to the measurement target gas, and corresponds to a so-called probe that is fixed at a place (measurement position) where the gas is to be measured, for example, inside a pipe. Since the gas detector 10 is connected to the light source and the light detector by the incident side optical fiber 20 and the light receiving side optical fiber 30, only the gas detector 10 is fixed at the measurement position, and the light source and the light detector are detected. Other devices, such as instruments, can be installed away from the measurement location.

The gas detection unit 10 includes a small optical bench 11, an incident side microlens 12, and a light receiving side microlens 13. The small optical bench 11 is a flat plate member having dimensions of several mm to several tens mm square.
Further, the small optical bench 11 is fixed with an incident side optical fiber fixing groove 14 for fixing a ferrule 21 provided at the tip of the incident side optical fiber 20 and a ferrule 31 provided at the tip of the light receiving side optical fiber 30. The light receiving side optical fiber fixing groove 15, the incident side micro lens fixing groove 16 for fixing the incident side micro lens 12, the light receiving side micro lens fixing groove 17 for fixing the light receiving side micro lens 13, and the micro mirror 18 are integrally formed. Has been.

The ferrule 21 of the incident side optical fiber 20 is in the incident side optical fiber fixing groove 14, the ferrule 31 of the light receiving side optical fiber 30 is in the light receiving side optical fiber fixing groove 15, and the incident side microlens 12 is in the incident side microlens fixing groove. 16, the light-receiving side microlens 13 is fitted in the light-receiving side microlens fixing groove 17 to constitute a Raman scattering optical system.
The micromirror 18 corresponds to the light reflector described in the claims.

  The Raman scattering phenomenon is a phenomenon in which when a substance such as a gas is irradiated with light, the wavelength of some scattered light changes due to molecular vibration or rotation of the substance. Such scattered light is called Raman scattered light. Further, it is known that the wavelength of Raman scattered light differs for each molecular species (gas species for gas and bonded molecular species for liquid), and there is a correlation between the concentration of gas and the intensity of Raman scattered light. Therefore, the gas type can be specified from the Raman scattered light wavelength, and the gas concentration can be specified from the Raman scattered light intensity.

  In the gas detector 10 according to the present embodiment, the laser light emitted from the tip of the incident side optical fiber 20 is incident on the measurement target gas, and the Raman scattered light emitted by the interaction between the laser light and the measurement target gas. The Raman scattering optical system which injects into the front-end | tip of the light reception side optical fiber 30 is comprised.

  More specifically, as shown in FIG. 2, one end of the gas detection unit 10 (left end in FIG. 2) is at the tip of the incident-side optical fiber 20 and the end surface is the other end of the gas detection unit 10 (in FIG. 2). It is fixed so that it faces the right end. A micromirror 18 having a flat reflecting surface is formed on the optical axis of the incident side optical fiber 20. The reflection surface of the micromirror 18 is substantially opposed to the end surface of the incident side optical fiber 20, and the angle thereof is such that the laser light L <b> 1 emitted from the incident side optical fiber 20 is directed toward or near the incident side optical fiber 20. It is set to be reflected. The angle of the reflection surface of the micromirror 18 is set to an angle at which the reflected laser light L2 does not directly enter the light receiving side optical fiber 30. For example, the angle formed by the optical axis of the incident side optical fiber 20 and the normal of the reflecting surface (incident angle of the laser light L1 emitted from the incident side optical fiber 20 to the micromirror 18) α is 0 ° to 30 °. Is set to

  Further, the tip of the light receiving side optical fiber 30 is fixed to the other end (the right end in FIG. 2) of the gas detection unit 10. The position and angle of the light receiving side optical fiber 30 are determined by the forward Raman scattered light Rf emitted by the interaction between the laser light L1 emitted from the incident side optical fiber 20 and the measurement target gas present in the gas detection unit 10, and The backward Raman scattered light Rb emitted by the interaction between the laser light L <b> 2 reflected by the micromirror 18 and the measurement target gas is set to enter the light receiving side optical fiber 30. The position and angle of the light receiving side optical fiber 30 are such that the laser light L1 emitted from the incident side optical fiber 20 and the laser light L2 reflected by the micromirror 18 are not directly incident on the light receiving side optical fiber 30 and It is set to an angle. For example, the angle β formed by the optical axis of the incident side optical fiber 20 and the optical axis of the light receiving side optical fiber 30 is set to 150 ° to 175 °.

  As shown in FIG. 3, the incident-side microlens 12 is disposed in front of the end face of the incident-side optical fiber 20, and the optical axis a thereof is disposed so as to coincide with the optical axis a of the incident-side optical fiber 20. ing. The incident-side microlens 12 is a convex lens, and is arranged so that the end surface of the incident-side optical fiber 20 is located at the focal point thereof. Therefore, the laser light emitted from the tip of the incident-side optical fiber 20 is converted into parallel rays. Can be.

  On the other hand, the light-receiving side microlens 13 is also arranged in front of the end face of the light-receiving side optical fiber 30 and is arranged so that its optical axis coincides with the optical axis of the light-receiving side optical fiber 30. The light-receiving side microlens 13 is a convex lens, and is arranged so that the end face of the light-receiving side optical fiber 30 is located at the focal point thereof. Therefore, Raman scattering emitted by the interaction between the laser light and the measurement target gas is used. The light can be collected and incident on the light receiving side optical fiber 30.

With the above optical system, the laser light L1 emitted from the tip of the incident side optical fiber 20 is incident on the measurement target gas existing in the gas detection unit 10 and is emitted by the interaction with the measurement target gas. The forward Raman scattered light Rf is incident on the tip of the light receiving side optical fiber 30. Further, the laser beam L1 that has passed through the measurement target gas is reflected by the micromirror 18 and is incident on the measurement target gas again. Then, the backward Raman scattered light Rb emitted by the interaction between the reflected laser light L <b> 2 and the measurement target gas can enter the tip of the light receiving side optical fiber 30.
As described above, since the forward Raman scattered light Rf and the backward Raman scattered light Rb are incident on the light receiving side optical fiber 30, the light intensity is increased compared to the case where only one of them is incident, and the sensitivity is high. Measurement target gas can be measured. Therefore, sufficient sensitivity can be maintained even if the gas detection unit 10 is downsized.

  In addition, since the optical gas sensor 1 includes a Raman scattering optical system in the gas detection unit 10, the measurement target gas can be measured by the Raman scattering method. Therefore, the optical gas sensor 1 has a high response speed in principle, and can measure a plurality of types of gases with one sensor by analyzing the spectrum of Raman scattered light, and there are few false alarm factors.

  In general, when a combustible gas comes in contact with an electric system such as an electrode or an electric wire, there is a risk of ignition or explosion. However, in the present embodiment, the gas detection unit 10 exposed to the measurement target gas does not have an electrical system, and thus is safe without the risk of ignition or explosion. Therefore, the optical gas sensor 1 can be attached to a site that requires detection of combustible gas, such as electric power equipment or a petrochemical plant.

  Incidentally, as shown in FIGS. 3 and 4, the small optical bench 11 is integrally formed with an incident side optical fiber fixing groove 14 constituted by a pair of wall bodies. The ferrule 21 of the incident side optical fiber 20 is fitted in the incident side optical fiber fixing groove 14.

Generally, the outer dimension of an optical fiber ferrule has a dimensional accuracy on the order of μm. Therefore, if the incident side optical fiber fixing groove 14 is formed with a positional accuracy and dimensional accuracy of the order of μm, the ferrule 21 can be positioned and arranged with an accuracy of the order of μm. Further, the general ferrule has a cylindrical shape concentric with an optical fiber inserted therein. Therefore, by bringing the side surface of the ferrule 21 into contact with the surface of the small optical bench 11, the optical axis a of the incident side optical fiber 20 can be made parallel to the surface of the small optical bench 11.
The ferrule 21 and the incident side optical fiber fixing groove 14 may be configured to be fixed by friction or may be fixed by an adhesive.

  As shown in FIGS. 3 and 5, the small optical bench 11 is integrally formed with an incident-side microlens fixing groove 16 composed of a pair of wall bodies. The entrance-side microlens fixing groove 16 has a substantially rhombic space in plan view, and the entrance-side microlens 12 is fitted in this space (see FIG. 1).

Here, the microlens is a lens having a diameter of several millimeters and generally has a dimensional accuracy on the order of μm. Therefore, if the incident-side microlens fixing groove 16 is formed with a positional accuracy and dimensional accuracy on the order of μm, the incident-side microlens 12 can be positioned and arranged with an accuracy on the order of μm. Further, when the incident-side microlens 12 having the same diameter as the ferrule 21 is employed, the incident-side optical fiber 20 can be obtained by bringing the outer peripheral edge of the incident-side microlens 12 into contact with the surface of the small optical bench 11. And the height of the optical axis a of the incident side microlens 12 can be matched.
The incident side microlens 12 and the incident side microlens fixing groove 16 may be configured to be fixed by friction or may be fixed by an adhesive.

  The light receiving side optical fiber fixing groove 15 and the light receiving side micro lens fixing groove 17 are also integrated with the small optical bench 11 with the same shape, position accuracy and dimensional accuracy as the incident side optical fiber fixing groove 14 and the incident side micro lens fixing groove 16. Is formed. Therefore, the ferrule 31 and the light receiving side microlens 13 of the light receiving side optical fiber 30 can also be arranged with an accuracy of the order of μm.

  The shape of each of the fixing grooves 14 to 17 is not limited to the shape described in the present embodiment, and any shape may be used as long as it is suitable for fixing the microlenses 12 and 13 and the optical fibers 20 and 30. Good. In addition, as long as the microlenses 12 and 13 and the optical fibers 20 and 30 can be fixed, a fixing portion having a non-groove shape may be employed.

As shown in FIG. 6, a micro mirror 18 that is a wall body perpendicular to the surface of the small optical bench 11 is integrally formed on the small optical bench 11. The light reflectance of the surface of the micromirror 18 is increased by a method such as plating, vacuum vapor deposition, or sputter vapor deposition.
The micromirror 18 is also formed with a positional accuracy and dimensional accuracy on the order of μm.

As described above, the small optical bench 11 includes the incident side optical fiber fixing groove 14, the light receiving side optical fiber fixing groove 15, the incident side microlens fixing groove 16, the light receiving side microlens fixing groove 17, and the micromirror 18. It is integrally formed with the positional accuracy and dimensional accuracy of the order.
Such a small optical bench 11 can be formed by, for example, a method such as photolithography, photofabrication, nanoimprinting, injection molding, or mold molding.

  For example, when the small optical bench 11 is formed by photolithography, a photosensitive resin such as SU-8 or polyimide is applied on a silicon substrate or a glass substrate to a thickness of 100 μm to 2 mm, and is exposed and developed. The optical fiber fixing groove 14, the light receiving side optical fiber fixing groove 15, the incident side microlens fixing groove 16, the wall constituting the light receiving side microlens fixing groove 17, and the micromirror 18 (hatched portion in FIG. 1) are made into a small optical bench. 11 can be integrally formed. In the case of using a negative photosensitive resin, a portion left as a structure is exposed, and in a case of using a positive photosensitive resin, a portion not left as a structure is exposed. Further, the light reflectance on the surface of the micromirror 18 can be increased by performing plating, vacuum deposition, sputter deposition, or the like on the entire small optical bench 11 after being formed by photolithography.

  If it is said formation method, each fixed groove 14-17 and the micromirror 18 can be integrally formed in the small optical bench 11 with high position accuracy and dimensional accuracy. Therefore, the ferrule 21 of the incident side optical fiber 20 is in the incident side optical fiber fixing groove 14, the ferrule 31 of the light receiving side optical fiber 30 is in the light receiving side optical fiber fixing groove 15, and the incident side microlens 12 is in the incident side microlens fixing groove. 16, the optimum Raman scattering optical system can be configured without adjustment by simply fitting the light receiving side microlens 13 into the light receiving side microlens fixing groove 17. As described above, since the adjustment mechanism of the optical system is unnecessary, the gas detection unit 10 can be reduced in size. And since the gas detection part 10 is small, the optical gas sensor 1 can be installed also in narrow places, such as the inside of piping, and can measure gas in various places.

In addition, since the small optical bench 11 can be formed in several mm to several tens mm square by the above-described formation method, the small gas detection unit 10 can be manufactured.
Furthermore, since the small optical bench 11 can be mass-produced by a method such as photolithography, photofabrication, nanoimprint, injection molding, mold molding, etc., the optical gas sensor 1 can be manufactured at low cost. Therefore, since the gas detection part 10 can be installed in many points, facilities, such as a plant, can be network-monitored in real time.

  In addition, the optimal optical system is designed in advance by optical simulation or the like, and the small optical bench 11 is formed based on the design. Therefore, by simply fixing the optical fibers 20 and 30 and the microlenses 12 and 13 to the small optical bench 11, an optimum optical system can be configured without adjustment.

  Furthermore, since each fixed groove 14-17 and the micromirror 18 are integrally formed in the small optical bench 11, the optical gas sensor 1 has few parts. Therefore, the frequency of failures is low and the durability is excellent.

(Second Embodiment)
The optical gas sensor 2 according to the second embodiment of the present invention is an optical gas sensor using a Raman scattering method. As shown in FIG. 7, the gas detection unit 10 of the optical gas sensor 2 according to the present embodiment is different from the Raman scattering optical system configured in the gas detection unit 10 of the optical gas sensor 1 according to the first embodiment. A Raman scattering optical system is configured.

  More specifically, the tip of the incident side optical fiber 20 is fixed to one end (the left end in FIG. 7) of the gas detection unit 10 so that the end surface thereof faces the other end (the right end in FIG. 7) of the gas detection unit 10. Has been. A micromirror 18 having a flat reflecting surface is formed on the optical axis of the incident side optical fiber 20. The reflection surface of the micromirror 18 is substantially opposed to the end surface of the incident side optical fiber 20, and the angle thereof is such that the laser light L <b> 1 emitted from the incident side optical fiber 20 is slightly away from the incident side optical fiber 20. It is set to be reflected toward. The angle of the reflection surface of the micromirror 18 is set to an angle at which the reflected laser light L2 does not directly enter the light receiving side optical fiber 30. For example, the angle formed by the optical axis of the incident side optical fiber 20 and the normal of the reflecting surface (incident angle of the laser light L1 emitted from the incident side optical fiber 20 to the micromirror 18) α is 5 ° to 30 °. Is set to

In addition, the tip of the light receiving side optical fiber 30 is fixed to one end of the gas detection unit 10 (left end in FIG. 7) along with the incident side optical fiber 20. The position and angle of the light receiving side optical fiber 30 are determined by the backward Raman scattered light Rb emitted by the interaction between the laser light L1 emitted from the incident side optical fiber 20 and the measurement target gas present in the gas detection unit 10, and The forward Raman scattered light Rf emitted by the interaction between the laser beam L2 reflected by the micromirror 18 and the measurement target gas is set to enter the light receiving side optical fiber 30. The position and angle of the light receiving side optical fiber 30 are such that the laser light L1 emitted from the incident side optical fiber 20 and the laser light L2 reflected by the micromirror 18 are not directly incident on the light receiving side optical fiber 30 and It is set to an angle. For example, the optical axis of the light receiving side optical fiber 30 and the normal of the reflecting surface are set to coincide with each other, and the angle β between the optical axis of the incident side optical fiber 20 and the optical axis of the light receiving side optical fiber 30 is 5 It is set to ° ~ 30 °.
Since the remaining configuration is the same as that of the optical gas sensor 1 according to the first embodiment, the same members are denoted by the same reference numerals and description thereof is omitted.

With the above optical system, the laser light L1 emitted from the tip of the incident side optical fiber 20 is incident on the measurement target gas existing in the gas detection unit 10 and is emitted by the interaction with the measurement target gas. The back Raman scattered light Rb is incident on the tip of the light receiving side optical fiber 30. Further, the laser beam L1 that has passed through the measurement target gas is reflected by the micromirror 18 and is incident on the measurement target gas again. Then, the forward Raman scattered light Rf emitted by the interaction between the reflected laser light L 2 and the measurement target gas can be incident on the tip of the light receiving side optical fiber 30.
As described above, since the forward Raman scattered light Rf and the backward Raman scattered light Rb are incident on the light receiving side optical fiber 30, the light intensity is increased compared to the case where only one of them is incident, and the sensitivity is high. Measurement target gas can be measured. Therefore, sufficient sensitivity can be maintained even if the gas detection unit 10 is downsized.

As described above, the gas detection unit 10 is fixed as a so-called probe inside a pipe or the like. Therefore, it is assumed that the gas detection unit 10 is inserted into the pipe from a gas detection hole provided in the pipe or the like. Further, it is assumed that the gas detection unit 10 is inserted into a place where a plurality of pipes are densely arranged or fixed to a narrowed part inside the pipes.
In the optical gas sensor 2 according to the present embodiment, since the distal ends of the incident side optical fiber 20 and the light receiving side optical fiber 30 are fixed to the same end of the gas detection unit 10, those cables extend in one direction. . Therefore, workability when inserting the gas detector 10 into the narrow space as described above is good.

(Third embodiment)
The optical gas sensor 3 according to the third embodiment of the present invention is an optical gas sensor using a Raman scattering method. As shown in FIG. 8, the gas detector 10 of the optical gas sensor 3 according to this embodiment includes a Raman scattering configured in the gas detector 10 of the optical gas sensors 1 and 2 according to the first and second embodiments. A Raman scattering optical system different from the optical system is configured.

  More specifically, the distal end of the incident side optical fiber 20 is fixed to one end (the left end in FIG. 8) of the gas detection unit 10 such that the end surface faces the other end (the right end in FIG. 8) of the gas detection unit 10. Has been. In addition, a pair of micromirrors 18 a and 18 b are formed at the other end (the right end in FIG. 8) of the gas detection unit 10 and spaced apart from each other with the optical axis of the incident side optical fiber 20 interposed therebetween. That is, a slit s located on the optical axis of the incident side optical fiber 20 is formed between the pair of micromirrors 18a and 18b. The reflecting surfaces of the micromirrors 18a and 18b are concave and substantially face the end surface of the incident side optical fiber 20. Then, the forward Raman scattered light Rf1 emitted by the interaction between the laser light L emitted from the incident side optical fiber 20 and the measurement target gas can be reflected and condensed at a position slightly away from the incident side optical fiber 20. It is like that.

  Further, the ends of the two light receiving side optical fibers 30a and 30b are fixed to one end (the left end in FIG. 8) of the gas detection unit 10 with the incident side optical fiber 20 interposed therebetween. The position and angle of one of the first light receiving side optical fibers 30a are set so that the forward Raman scattered light Rf2 reflected and collected by one micromirror 18a is incident on the first light receiving side optical fiber 30a. Yes. The position and angle of the other second light receiving side optical fiber 30b are set so that the forward Raman scattered light Rf2 reflected and collected by the other micromirror 18b is incident on the second light receiving side optical fiber 30b. Yes. The other ends of the two light receiving side optical fibers 30a and 30b are connected to a common photodetector or to different photodetectors, and the light intensity is measured by a computer or the like to which the photodetectors are connected. Can be added.

Since the remaining configuration is the same as that of the optical gas sensor 1 according to the first embodiment, the same members are denoted by the same reference numerals and description thereof is omitted.
Reference numerals 31a and 31b are ferrules of the first light receiving side optical fiber 30a and the second light receiving side optical fiber 30b, respectively. Reference numerals 13a and 13b are respectively the first light receiving side optical fiber 30a and the second light receiving side optical fiber 30b. The incident side microlens arranged at the front of the end face, reference numerals 15a and 15b are light receiving side optical fiber fixing grooves for fixing the ferrules 31a and 31b, and reference numerals 17a and 17b are respectively fixed to the incident side microlenses 13a and 13b. This is a light receiving side microlens fixing groove.

If it is said optical system, the laser beam L radiate | emitted from the front-end | tip of the incident side optical fiber 20 will inject into the measuring object gas which exists in the gas detection part 10, and will be radiate | emitted by the interaction with the measuring object gas. The forward Raman scattered light Ra1 is reflected and condensed by the micromirrors 18a and 18b, and can enter the front ends of the light receiving side optical fibers 30a and 30b.
Thus, since the forward Raman scattered light Rf1 emitted on both sides of the optical fiber of the incident side optical fiber 20 is incident on the light receiving side optical fibers 30a and 30b, the forward Raman scattering emitted only on one side is entered. The light intensity is stronger than when the light Rf1 is incident, and the measurement target gas can be measured with high sensitivity. Therefore, sufficient sensitivity can be maintained even if the gas detection unit 10 is downsized.

  Further, since the laser light L emitted from the incident side optical fiber 20 passes through the slit s between the pair of micromirrors 18a and 18b, it does not enter the light receiving side optical fibers 30a and 30b. Raman scattered light has directivity distributed in front and rear of incident light, but is known to have lower light intensity than incident light. Therefore, as in this embodiment, by not allowing the laser light L to enter the light receiving side optical fibers 30a and 30b, disturbance components are reduced and measurement accuracy is improved.

  Furthermore, since the tips of the incident side optical fiber 20 and the light receiving side optical fibers 30a and 30b are fixed to the same end of the gas detection unit 10, these cables extend in one direction. Therefore, workability when inserting the gas detector 10 in a narrow place is good.

(Fourth embodiment)
The optical gas sensor 4 according to the fourth embodiment of the present invention is an optical gas sensor using an absorption measurement method. As shown in FIG. 9, the optical gas sensor 4 is connected to the gas detection unit 10 and the gas detection unit 10 in the same manner as the optical gas sensors 1, 2, and 3 according to the first, second, and third embodiments. The incident side optical fiber 20 and the light receiving side optical fiber 30 are provided.

The gas detection unit 10 includes a small optical bench 11, an incident side microlens 12, and a light receiving side microlens 13. The small optical bench 11 is a flat plate member having dimensions of several mm to several tens mm square.
Further, the small optical bench 11 is fixed with an incident side optical fiber fixing groove 14 for fixing a ferrule 21 provided at the tip of the incident side optical fiber 20 and a ferrule 31 provided at the tip of the light receiving side optical fiber 30. The light receiving side optical fiber fixing groove 15, the incident side micro lens fixing groove 16 for fixing the incident side micro lens 12, and the light receiving side micro lens fixing groove 17 for fixing the light receiving side micro lens 13 have a positional accuracy of μm order, It is integrally formed with dimensional accuracy.

The small optical bench 11 can be formed by, for example, photolithography, photofabrication, nanoimprint, injection molding, mold molding, or the like.
If it is said formation method, each fixed groove 14-17 can be integrally formed in the small optical bench 11 with high position accuracy and dimensional accuracy. Therefore, the ferrule 21 of the incident side optical fiber 20 is in the incident side optical fiber fixing groove 14, the ferrule 31 of the light receiving side optical fiber 30 is in the light receiving side optical fiber fixing groove 15, and the incident side microlens 12 is in the incident side microlens fixing groove. 16 and the light receiving side microlens 13 is fitted into the light receiving side microlens fixing groove 17, respectively, and an optimum light absorbing optical system can be configured without any adjustment. As described above, since the adjustment mechanism of the optical system is unnecessary, the gas detection unit 10 can be reduced in size.

In addition, since the small optical bench 11 can be formed in several mm to several tens mm square by the above-described formation method, the small gas detection unit 10 can be manufactured.
Furthermore, since the small optical bench 11 can be mass-produced, the optical gas sensor 4 can be manufactured at low cost.

Next, the absorption optical system configured in the gas detection unit 10 will be described.
The absorption measurement method is a method for quantitatively analyzing the concentration of the measurement target gas from the absorbance when the light enters the measurement target gas and the incident light passes through the measurement target gas. Moreover, the gas species can also be specified from the peak wavelength of the light absorption spectrum.

In the gas detection unit 10 according to the present embodiment, light emitted from the tip of the incident side optical fiber 20 is incident on the measurement target gas, and light emitted through the measurement target gas is incident on the tip of the light receiving side optical fiber 30. More specifically, as shown in FIG. 9, at one end of the gas detection unit 10 (left end in FIG. 9), the tip of the incident-side optical fiber 20 and its end face are formed. The gas detector 10 is fixed so as to face the other end (the right end in FIG. 9). Further, the other end (the left end in FIG. 9) of the gas detection unit 10 is fixed such that the tip of the light receiving side optical fiber 30 faces the end surface of the incident side optical fiber 20. That is, the incident side optical fiber 20 and the light receiving side optical fiber 30 are fixed to face each other on the same optical axis.

  With the optical system described above, the laser beam emitted from the tip of the incident side optical fiber 20 is incident on the measurement target gas existing in the gas detection unit 10, and the emission light that has passed through the measurement target gas is converted into the light reception side optical fiber 30. Can be incident on the tip.

  As described above, since the optical gas sensor 4 includes the light absorption optical system in the gas detection unit 10, the measurement target gas can be measured by the absorption measurement method. Since the optical gas sensor 4 measures the gas to be measured by the absorption measurement method, in principle, the response speed is fast, and by analyzing the light absorption spectrum, one type of gas can be measured by one sensor, and there is a false alarming factor. Few.

Further, since there is no electrical system in the gas detection unit 10 exposed to the measurement target gas, there is no risk of ignition or explosion and it is safe.
Furthermore, since each fixed groove 14-17 is integrally formed in the small optical bench 11, the optical gas sensor 4 has few parts. Therefore, the frequency of failures is low and the durability is excellent.

(Fifth embodiment)
The optical gas sensor 5 according to the fifth embodiment of the present invention is an optical gas sensor using an absorption measurement method. As shown in FIG. 10, the gas detection unit 10 of the optical gas sensor 5 according to the present embodiment has an absorbance different from that of the absorption optical system configured in the gas detection unit 10 of the optical gas sensor 4 according to the fourth embodiment. An optical system is configured.

More specifically, as shown in FIG. 10, the incident side optical fiber 20 and the light receiving side optical fiber 30 are fixed to one end (left end in FIG. 10) of the small optical bench 11 so that the respective optical axes are parallel. Has been. In addition, three micromirrors 18a, 18b, and 18c are integrally formed on the small optical bench 11 with a positional accuracy and dimensional accuracy on the order of μm. Among these, the micromirror 18 a is disposed on the optical axis of the incident side optical fiber 20, and the micromirror 18 c is disposed on the optical axis of the light receiving side optical fiber 30. In addition, the micromirror 18 b is disposed between the incident side optical fiber 20 and the light receiving side optical fiber 30. The angle of the micromirror 18a is set so as to reflect the light emitted from the incident side optical fiber 20 toward the micromirror 18b, and the angle of the micromirror 18b allows the light from the micromirror 18a to be microscopically reflected. The angle of the micromirror 18c is set so as to reflect the light from the micromirror 18b toward the light receiving side optical fiber 30.
Since the remaining structure is the same as that of the optical gas sensor 4 according to the fourth embodiment, the same members are denoted by the same reference numerals and description thereof is omitted.

If it is said optical system, the light radiate | emitted from the front-end | tip of the incident side optical fiber 20 will be reflected in measurement object gas 3 times by three micromirrors 18a, 18b, 18c, and the emitted light which passed the measurement object gas will be reflected. The light can enter the front end of the light receiving side optical fiber 30.
Thus, since the light emitted from the tip of the incident side optical fiber 20 is reflected many times in the measurement target gas, the optical path length becomes long, and the measurement target gas can be measured with high sensitivity. Therefore, sufficient sensitivity can be maintained even if the gas detection unit 10 is downsized.

  Furthermore, since the tips of the incident side optical fiber 20 and the light receiving side optical fiber 30 are fixed to the same end of the gas detection unit 10, these cables extend in one direction. Therefore, workability when inserting the gas detector 10 in a narrow place is good.

(Other embodiments)
The optical system configured in the gas detection unit 10 in the above embodiment is an example, and other various optical systems may be configured in the gas detection unit 10.
For example, in the first embodiment, the micromirror 18 may not be provided, and the forward Raman scattered light emitted by the interaction with the measurement target gas may be directly incident on the tip of the light receiving side optical fiber 30.
Further, in the second embodiment, the micromirror 18 may not be provided, and the backward Raman scattered light emitted by the interaction with the measurement target gas may be directly incident on the tip of the light receiving side optical fiber 30.
In these cases, if a plurality of light receiving side optical fibers 30 are provided, the Raman scattered light can be received efficiently, so that the measurement accuracy is improved. When a plurality of light receiving side optical fibers 30 are provided, all the light receiving side optical fibers may be configured to receive forward Raman scattered light or backward Raman scattered light, or a part of the light receiving side optical fibers. 30 may receive forward Raman scattered light, and the remaining light receiving side optical fiber 30 may receive backward Raman scattered light.

  In the fifth embodiment, the number of micromirrors 18a, 18b, 18c may be less than or greater than three. If a larger number of micromirrors are provided, the optical path length can be increased. However, if the number of reflections is large, the light intensity of the outgoing light incident on the light receiving side optical fiber 30 becomes weak due to the reflectance of the light of the micromirrors. Therefore, it is preferable to adopt an optimum optical system in consideration of the optical path length and the reflectance.

  In addition to a plane mirror, a mirror having a curved surface such as a concave mirror or a convex mirror may be employed as the micromirror. Further, instead of the micromirror, other light reflectors such as a grating that reflects light of a specific wavelength may be provided. When a light reflector formed as a separate member from the small optical bench 11 such as a grating is employed, a fixed portion may be integrally formed on the small optical bench 11 and the light reflector may be fixed to the fixed portion. . Furthermore, the present invention is not limited to lenses and mirrors, and various other optical components may be employed. In this case, a fixed portion may be integrally formed on the small optical bench 11 and the optical component may be fixed to the fixed portion.

[Light intensity test]
Example 1
Using the optical gas sensor 1 according to the first embodiment (see FIGS. 1 and 2), the light intensity of the Raman scattered light incident on the light receiving side optical fiber 30 was measured.
In the Raman scattering optical system configured in the gas detection unit 10 of the optical gas sensor 1 used for the test, the angle α formed by the optical axis of the incident side optical fiber 20 and the normal line of the reflection surface of the micromirror 18 is 8.6 °, The angle β formed by the optical axis of the incident side optical fiber 20 and the optical axis of the light receiving side optical fiber 30 is 151.9 °, and the distance between the incident side microlens 12 and the micromirror 18 on the optical axis of the incident side optical fiber 20. Is 20.0 mm, and the distance between the light receiving side microlens 13 and the optical axis of the incident side optical fiber 20 on the optical axis of the light receiving side optical fiber 30 is set to 9.55 mm. Further, a second harmonic laser beam of an Nd: YAG laser (Explorer made by SpectraPhysics Co., Ltd.) having an oscillation wavelength of 532 nm as a light source connected to the incident side optical fiber 20, and a photomultiplier as a photodetector connected to the light receiving side optical fiber 30. A tube (R3896 manufactured by Hamamatsu Photonics) was used. Then, hydrogen gas having a concentration of 100% was introduced into the gas detector 10 and the signal intensity obtained by the photodetector was measured.
As a result, a signal indicated by a black line in the graph of FIG. 11 was obtained from the photodetector.

(Comparative Example 1)
In the optical gas sensor 1 of Example 1 described above, a test was performed under the same conditions as in Example 1 using an optical gas sensor in which the micromirror 18 was not provided.
As a result, a signal indicated by a gray line in the graph of FIG. 11 was obtained from the photodetector.

As shown in FIG. 11, it was confirmed that the signal intensity of Example 1 was twice or more stronger than the signal intensity of Comparative Example 1. This is because both forward Raman scattered light and backward Raman scattered light are incident on the light receiving side optical fiber 30 in the first embodiment, whereas only forward Raman scattered light is incident on the light receiving side optical fiber 30 in the comparative example. Because.
From the above, it has been confirmed that if the Raman scattering optical system in the first embodiment is configured, the light intensity of the Raman scattered light incident on the light receiving side optical fiber 30 is increased, and the measurement target gas can be measured with high sensitivity.

[Sensitivity test]
(Example 2)
The sensitivity to the gas concentration was measured using the optical gas sensor 4 (see FIG. 9) according to the fourth embodiment.
In the light absorption optical system configured in the gas detector 10 of the optical gas sensor 4 used for the test, the distance between the incident side microlens 12 and the light receiving side microlens 13 is set to 10 mm. Also, a deuterium lamp (L10671 manufactured by Hamamatsu Photonics) was used as the light source connected to the incident side optical fiber 20, and a spectrometer with a CCD array (USB2000 + manufactured by Ocean Optics) was used as the photodetector connected to the light receiving side optical fiber 30. . Then, various concentrations of ammonia gas (NH ₃ ) were introduced into the gas detector 10 and the absorbance at each concentration was measured.
As a result, the graph of FIG. 12 was obtained.

  As shown in FIG. 12, it was confirmed that when the optical gas sensor 4 of Example 2 was used, it was possible to sufficiently detect up to 25 ppm, which is the allowable toxicity concentration of ammonia gas.

1, 2 Optical gas sensor,
10 gas detector,
11 Small optical bench,
12 Incident side microlens,
13 Light receiving side microlens,
14 Incident side optical fiber fixing groove,
15 Receiving side optical fiber fixing groove,
16 Incident side microlens fixing groove,
17 Light receiving side microlens fixing groove,
18 Micromirror,
20 incident side optical fiber,
30 receiving side optical fiber,

Claims (4)

An incident-side optical fiber having one end connected to the light source;
A light receiving side optical fiber having one end connected to the photodetector;
An optical system is configured in which light emitted from the other end of the incident side optical fiber is incident on the measurement target gas and light emitted by interaction with the measurement target gas is incident on the other end of the light receiving side optical fiber. A gas detection unit,
The gas detection unit
With a small optical bench,
The small optical bench includes
An incident side optical fiber fixing portion for fixing the other end of the incident side optical fiber;
A light receiving side optical fiber fixing portion for fixing the other end of the light receiving side optical fiber;
And a light reflector that reflects light are integrally formed,
In the gas detector,
The incident-side optical fiber that makes light incident on the measurement object gas; and
The light reflector disposed on the optical axis of the incident side optical fiber and reflecting the light emitted from the incident side optical fiber at an angle not directly incident on the light receiving side optical fiber ;
Forward Raman scattered light emitted by the interaction between the light emitted from the incident side optical fiber and the measurement object gas, and the interaction between the light reflected by the light reflector and the measurement object gas backward Raman scattered light, optical and gas sensor you characterized in that the arranged light receiving side optical fiber at a position that is incident without passing through the reflection, Raman scattering optical system from being configured to be. An incident-side optical fiber having one end connected to the light source;
A light receiving side optical fiber having one end connected to the photodetector;
An optical system is configured in which light emitted from the other end of the incident side optical fiber is incident on the measurement target gas and light emitted by interaction with the measurement target gas is incident on the other end of the light receiving side optical fiber. A gas detection unit,
The gas detection unit
With a small optical bench,
The small optical bench includes
An incident side optical fiber fixing portion for fixing the other end of the incident side optical fiber;
A light receiving side optical fiber fixing portion for fixing the other end of the light receiving side optical fiber;
And a light reflector that reflects light are integrally formed,
In the gas detector,
The incident-side optical fiber that makes light incident on the measurement object gas; and
The light reflector disposed on the optical axis of the incident side optical fiber and reflecting the light emitted from the incident side optical fiber at an angle not directly incident on the light receiving side optical fiber ;
Back Raman scattered light emitted by the interaction between the light emitted from the incident side optical fiber and the measurement object gas, and the interaction between the light reflected by the light reflector and the measurement object gas forward Raman scattered light, is disposed at a position that is incident without passing through the reflection was the light receiving side optical fiber and, optical and gas sensor you characterized by Raman scattering optical system is composed of being. An incident-side optical fiber having one end connected to the light source;
A light receiving side optical fiber having one end connected to the photodetector;
An optical system is configured in which light emitted from the other end of the incident side optical fiber is incident on the measurement target gas and light emitted by interaction with the measurement target gas is incident on the other end of the light receiving side optical fiber. A gas detection unit,
The gas detection unit
With a small optical bench,
The small optical bench includes
An incident side optical fiber fixing portion for fixing the other end of the incident side optical fiber;
A light receiving side optical fiber fixing portion for fixing the other end of the light receiving side optical fiber;
And a light reflector that reflects light are integrally formed,
In the gas detector,
The incident-side optical fiber that makes light incident on the measurement object gas; and
A pair that is arranged at a predetermined interval across the optical axis of the incident side optical fiber and reflects forward Raman scattered light emitted by the interaction between the light emitted from the incident side optical fiber and the measurement object gas. Said light reflector,
It said pair of optical and gas sensor you characterized by Raman scattering optical system from said light receiving side optical fiber disposed at a position forward Raman scattered light reflected incident, the light reflector is formed. The miniature optical bench, photolithography, photo-fabrication, nanoimprint, injection molding, according to claim 1, 2 or 3 optical type, wherein the is one formed by any one of means of molding Gas sensor.