JPH0481738B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an essentially explosion-proof optical sensor that detects hydrogen gas concentration in an all-optical manner, which is useful in oil refining plants and the like.

[Description of prior art]

A conventional all-optical hydrogen detection sensor of this type is shown in FIG.

In the figure, an optical waveguide 2 is formed on a dielectric substrate 1, and this waveguide 2 is connected to an input optical fiber 3A.
It consists of an input waveguide 2A to which is connected, and branch waveguides 2B and 2C that branch into two in a Y-shape from this input waveguide 2A and reach the other end surface of the substrate. Output optical fiber 3
B and 3C are connected respectively.

Of the branch waveguides 2B and 2C, one 2B is a hydrogen detection waveguide and the other 2C is a reference optical waveguide, and on the former waveguide 2B is a dielectric material that reacts with hydrogen and changes its light absorption coefficient. A thin film 4 consisting of
A metal thin film 5 for dissociating and adsorbing hydrogen gas is further laminated on this thin film 4.

In the above sensor, most of the light propagating through the waveguide 2B is confined within this waveguide, but some of it leaks into the dielectric thin film 4 as evanescent light.

When hydrogen gas comes into contact with the surface thin film 5, the hydrogen is dissociated and adsorbed by this thin film, and this dissociated hydrogen reacts with the base film 4 to color the underground film 4, and the evanescent light is absorbed and attenuated in the film 4. , the amount of light emitted to the output optical fiber 3B decreases. Therefore, by comparing this emitted light amount with the light amount of the reference light emitted from the branch waveguide 2C in which the thin film is not provided, the hydrogen gas concentration can be detected from the amount of change in the light amount difference. .

[Problem that the invention seeks to solve]

In the conventional all-optical hydrogen detection sensor described above, the optical fiber is at least one input side and two output sides of the waveguide.
A total of three optical fibers are required, and since these optical fibers are located on opposite sides of the waveguide, complicated means are required to protect and hold the optical fibers when actually installing them in various plants and equipment. The disadvantage was that the workability of installation and maintenance was poor.

[Means to solve problems]

A dielectric thin film whose light absorption coefficient changes by reacting with hydrogen is laminated on the side of the optical waveguide formed on the substrate, and the surface of the thin film is coated with a metal thin film that dissociates and adsorbs hydrogen gas, In addition, a reflector was provided in close contact with one end face of the waveguide, and an input/output optical fiber was connected to the other end face to constitute a hydrogen detection sensor.

[Effect]

In the sensor with the above configuration, when light is introduced into the waveguide through the input/output optical fiber, the propagating light propagates inside the waveguide and is then reflected by the reflector provided at the other end, causing the same waveguide to pass through the same waveguide. The light returns and is emitted to the input/output optical fiber again. When hydrogen gas is adsorbed, the thin film on the waveguide becomes colored, and the evanescent light that seeps out of the waveguide and passes through the thin film is attenuated during reciprocating propagation through the waveguide.

In this way, compared to the conventional one, it is equivalent to providing a detection waveguide that is substantially twice the length using a waveguide element of the same length, and the detection sensitivity can be improved accordingly. As a result, only a single optical fiber connection is required, so the overall size of the device can be reduced, and assembly, installation, and maintenance operations are greatly facilitated.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments shown in the drawings.

In FIGS. 1 and 2, reference numeral 10 denotes a substrate that is transparent to the wavelength used, and a single linear optical waveguide 11 is embedded in this substrate 10.

The waveguide 11 is formed, for example, by thermally diffusing Ti into the substrate 10 made of LiNbO ₃ or by ion-exchange diffusion of monovalent cations such as Tl, which contribute to increasing the refractive index of glass, into the glass substrate 10. can do. A light absorption layer 12 is provided on the upper part of the optical waveguide 11 so as to cover almost the entire length of the waveguide and at least the entire width of the waveguide, and a hydrogen adsorption layer 13 is further laminated on the light absorption layer 12. There is. The hydrogen adsorption layer 13 is made of a substance that adsorbs and dissociates hydrogen gas to generate electrons and protons, and the light absorption layer 12 is made of a substance whose light absorption coefficient changes upon receiving the electrons and protons.

As the material for the above adsorption layer 13, palladium (Pd) or platinum (Pt) is suitable.

Moreover, as a substance forming the light absorption layer 12,
WO ₃ is suitable, and other inorganic materials that are generally electrochromic, such as M ₀ O ₃ , V ₂ O ₅ ,
TiO ₂ , Ir(OH) _o , Rh ₂ O ₃ .XH ₂ O, etc. can be used.

The light absorption layer 12 may be made of an organic material, such as hepyl viologen, cyanophenyl viologen, cobalt biridyl complex, polymerized tetrathiofulvalene (TTF), or lutetium diphthalocyanine.

A reflector 14 is provided in close contact with an end surface 11A of the optical waveguide 11 exposed on one end surface 10A of the substrate 10. This reflector 14 is for example
It is formed by attaching a highly reflective metal film such as Al or Ag to the above surface by vapor deposition, sputtering, or the like.
Alternatively, a reflection film provided on a separate base material surface may be bonded to the waveguide end face. A dielectric reflective film can also be used. Further, an optical fiber 15 for both input and output is optically connected to the other end surface 11B of the optical waveguide 11. In the hydrogen detection sensor 20 having the above configuration, when the transmitted light is made to enter the optical waveguide 11 through the optical fiber 15, the optical waveguide 1
After propagating through the optical fiber 1, the entire amount of the propagating light is reflected by the reflector 14 at the other end, returns to the optical waveguide 11 again, and is emitted to the optical fiber 15.

When hydrogen gas comes into contact with the adsorption layer 13, it is dissociated and adsorbed, and the dissociated hydrogen reacts with the light absorption layer 12, increasing the light absorption coefficient of the absorption layer 12.

For example, when WO ₃ is used as the light absorption layer 12, what was initially transparent becomes colored tungsten bronze. As a result, the evanescent light portion of the guided light propagating through the optical waveguide 11 is absorbed by the light absorption layer 12 and attenuated. This light absorption attenuation occurs during the round trip when the light travels within the waveguide 11 toward the reflector 14, is reflected by the reflector 14, and returns toward the optical fiber 15; therefore, it occurs over a relatively short distance. Even if the wave path 11 is used, or even if the concentration of hydrogen gas is low, sufficient attenuation of the amount of light occurs.

In this way, by connecting a light receiving element to the other end of the optical fiber 15 and measuring changes in the amount of received light, it is possible to detect the generation of hydrogen gas and its concentration at the location where the sensor is disposed.

FIG. 4 shows another example of the structure of the sensor of the present invention.
In this example, in order to improve the moisture resistance of the sensor, a hydrogen selective permeable membrane 16 made of a material with excellent weather resistance is provided on the outside of the hydrogen adsorption layer 13 so as to cover both layers 12 and 13 entirely. This selectively permeable membrane 16 is a coating having a microscopic pore size that allows _hydrogen to permeate selectively while blocking the permeation of water vapor. It can be formed by depositing it to a thickness of .

FIG. 3 shows an example of a hydrogen detection system using the sensor according to the present invention.

In the figure, light from a light emitting device 31 passes through an input optical fiber 32 and enters a directional coupler 33.
Here, part of the light is transmitted to the input/output optical fiber 15 and the remaining light is transmitted to the monitor optical fiber 37. The light propagating through the input/output optical fiber 15 reaches the reflective hydrogen detection sensor 20, undergoes attenuation according to the hydrogen gas concentration, returns to the directional coupler 33 through the input/output optical fiber 15, and a portion of the light is transmitted through the input/output optical fiber 15. Light reaches output optical fiber 36. Output optical fiber 36
The light from the monitor optical fiber 37 and the light from the monitor optical fiber 37 are converted into electrical signals by the light receiving devices 38 and 39, respectively, and compared by the arithmetic device 40.

Next, to show a specific numerical example of the present invention, the substrate 1
LiNbO ₃ was used as a reflector 14, and Ti was thermally diffused thereto to form an optical waveguide 11. After polishing both end faces of the substrate 10 at right angles to the waveguide, aluminum was used as a reflector 14 on the end face of the waveguide. Vacuum deposited to a thickness of angstroms. Further, a WO ₃ thin film was vacuum-deposited as a light absorption layer 12 on the waveguide 11 to a thickness of 1 μm. WO ₃ was ion plated using pellets with a purity of 99.99% and evaporated by resistance heating using a W-wire crucible coated with alumina.
The deposition conditions were an oxygen pressure of 1×10 ⁻⁴ Torr, ionization high-frequency power of 200 W, and ion acceleration voltage of −500 V. The substrate temperature during deposition was room temperature, and the obtained
The WO ₃ film was amorphous and colorless and transparent.

Further, Pd was deposited thereon as an adsorption layer 13 to a thickness of 100 angstroms by electron beam heating vapor deposition.

When the above sensor was incorporated into the measurement system shown in Figure 3 and the hydrogen gas concentration was measured, it was found that 20~
It was possible to measure a concentration range of 2000 ppm with an accuracy of ±5%.

〔Effect of the invention〕

According to the present invention, the hydrogen detection sensor and the measurement system can be connected with a single optical fiber, which is economical, and also improves workability in installation and maintenance.

Furthermore, since light is absorbed and attenuated during both the forward and backward propagation processes of the waveguide, the device can be made smaller compared to conventional structures, and at the same time, the detection sensitivity can be greatly improved with the same size device.

Further, even if the waveguide pattern is a simple single straight path, sufficient detection sensitivity can be obtained, so manufacturing is easy.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing an embodiment of the present invention, FIG. 2 is a plan view thereof, and FIG. 3 is a block diagram showing an example of an all-optical hydrogen detection system incorporating the sensor of the present invention. FIG. 4 is a cross-sectional view showing another embodiment of the present invention, and FIG. 5 is a perspective view showing a conventional hydrogen detection sensor. 10... Substrate, 11... Optical waveguide, 12... Light absorption layer, 13... Adsorption layer, 14... Reflector, 15
...Input/output optical fiber, 16...Hydrogen selective transmission protective coating, 20...Hydrogen detection optical sensor, 31...
Light emitting device, 32, 36, 37... Optical fiber, 3
3... Directional coupler, 38, 39... Light receiving device,
40...Arithmetic device.

Claims (1)

[Claims] 1. Laminating a dielectric thin film whose light absorption coefficient changes by reacting with hydrogen on the top of the optical waveguide formed on the substrate, and coating the surface of the thin film with a metal thin film that dissociates and adsorbs hydrogen gas, A reflective hydrogen detection optical sensor characterized in that a reflector is provided in close contact with one end face of the waveguide, and an input/output optical fiber is connected to the other end face.