JPH0513458B2 - - 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 using an all-optical method.

[Description of prior art]

A conventional all-optical hydrogen detection optical sensor of this type has a structure shown in FIG.

In the figure, an optical waveguide 2 is formed on a dielectric substrate 1, and a light absorption layer 3 made of a substance whose light absorption coefficient changes by reacting with hydrogen is provided on the exposed upper surface of the optical waveguide 2. An adsorption layer 4 made of a metal film that dissociates and adsorbs hydrogen gas is laminated on top of the layer 3. An input optical fiber 5A and an output optical fiber 5B are connected to both ends of the optical waveguide 2, respectively.

When hydrogen gas comes into contact with the adsorption layer 4 on the surface of the above sensor, it is dissociated and adsorbed, and the light absorption layer 3 below the dissociated hydrogen reacts, changing its light absorption coefficient.
Most of the guided light propagating through the optical waveguide 2 is confined in the waveguide, but some of it leaks into the light absorption layer 3 as evanescent light, so the light absorption coefficient of the light absorption layer 3 changes due to hydrogen contact. When it increases, the evanescent light is absorbed and attenuated, and the amount of light emitted to the output optical fiber 5B decreases.

Therefore, the hydrogen gas concentration can be determined by measuring the change in the amount of light emitted from the output optical fiber 5B.

[Problem that the invention seeks to solve]

In the above-mentioned conventional structure, the surface of the hydrogen gas adsorption layer 4 is in constant contact with the outside air, and therefore is susceptible to reactions with various substances other than hydrogen gas, and in particular, by reacting with water vapor, the adsorption layer 4 and There was a problem that the reactivity of the light absorption layer 3 to hydrogen gas deteriorated early.

[Means for solving problems]

The entire surface of the adsorption layer 4 was coated with a selectively permeable coating that was permeable to hydrogen gas and impermeable to at least water vapor.

[Effect]

Hydrogen gas passes through the selectively permeable membrane and is dissociated and adsorbed by the hydrogen gas adsorption layer as in the conventional method, and the light absorption coefficient of the light absorption layer that reacts with the dissociated hydrogen changes, changing the amount of light emitted from the optical waveguide. .

On the other hand, water vapor is prevented from entering by the selectively permeable membrane, and the exposed surfaces and side edges of the adsorption layer and light absorption layer are protected, so stable hydrogen detection performance is maintained over a long period of time.

〔Example〕

The present invention will be described in detail below based on embodiments shown in the drawings.

In FIGS. 1 and 2, 10 is a substrate;
1 is an optical waveguide, and the waveguide 11 is, for example,
It is formed by means such as thermal diffusion of Ti into a LiNbO ₃ substrate or ion exchange diffusion into a glass substrate.
A light absorption layer 12 is laminated on the substrate so as to cover the exposed surface of the waveguide 11 except for the vicinity of both ends of the entire length of the optical waveguide 11, and an adsorption layer 13 is further formed on the light absorption layer 12. It's layered.

The adsorption layer 13 adsorbs and dissociates hydrogen gas to generate electrons and
The light absorption layer 12 is made of a metal thin film that generates protons, and the light absorption layer 12 is made of a dielectric thin film whose light absorption coefficient changes in response to the electrons and protons mentioned above.

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

In addition, as a substance forming the light absorption layer 12,
WO ₃ is preferred; other inorganic materials that are generally electrochromic, such as MoO ₃ , V ₂ O ₅ ,
TiO ₂ , Ir(OH)n, 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 hep-er viologen, cyanophenol viologen, cobalt pyridyl complex, polymerized tetrathiofulvalene (TTF), lutetium diphthalocyanine, or the like. The surface of the adsorption layer 13 and the entire circumferential side edges of the adsorption layer 13 and light absorption layer 12 are covered with a hydrogen gas selective permeation film 14 for protection. This coating 14 is formed of a thin film of a material with excellent weather resistance, such as a SiO ₂ film, having micropores that allow hydrogen gas to pass therethrough and at least block water vapor permeation.

As an example, using electron beam heating evaporation method, high-purity
SiO pellets are used as the evaporation source, oxygen pressure is 1×
The film 14 having the above function is obtained by depositing a SiO ₂ film with a thickness of about 500 angstroms under the conditions of 10 ^-4 Torr, ionization high frequency power of 50 W, and ion acceleration voltage of -500 V. In addition to SiO ₂ , zeolite, alumina, etc. can also be used as the coating 14.

Note that the coating 14 may be provided only in the region where the adsorption layer 13 and the light absorption layer 12 are formed, but if it is formed over the entire length of the optical waveguide 11 as shown in the illustrated example, it will also protect the waveguide 11. So it's convenient.

In the above case, since the coating portion 14B in the area outside both layers 12 and 13 does not require selective hydrogen permeability as described above, the coating protection portion 14B of both layers 12 and 13 does not require hydrogen selective permeability as described above.
In order to reduce propagation loss, it is desirable to smooth the interface with the waveguide by applying local heating to the other coating portion 14B, leaving the coating portion 4A, by irradiating with a CO ₂ laser or the like.

An input optical fiber 15A is connected to one end of the optical waveguide 11 of the sensor element 20 configured as described above, and an output optical fiber 15B is connected to the other end.

The sensor element 20 is placed at the detected location, and the other end of the input optical fiber 15A is connected to a light source device 16 such as a semiconductor laser located at a remote location.
The other end of the output optical fiber 15B is connected to the photodetector 17. The light emitted from the light source device 16 is transmitted through the optical fiber 15A, enters the optical waveguide 11 of the sensor element 20, and propagates through the waveguide 11. A part of the propagated light leaks into the light absorption layer 12 as evanescent light. The amount of seepage of this evanescent light is determined by the curvature of the light absorption layer 12 and the waveguide 11.
can be as large as about 20%, depending on the magnitude of the curvature. When hydrogen gas is present at the location where the sensor element 20 is installed, the hydrogen gas passes through the protective coating 14 and comes into contact with the adsorption layer 13, for example, a Pd thin film, and is dissociated and adsorbed, and this dissociated hydrogen is absorbed into the light absorption layer 12.
The light absorption coefficient of the absorption layer 12 changes as a result of the reaction.

For example, when the light absorption layer 12 is made of WO ₃ , tungsten bronze is produced and colored.

As a result, the evanescent light of the guided light propagating through the optical waveguide 11 is absorbed and attenuated in the WO ₃ layer, and the amount of light received by the photodetector 17 is reduced. Since the amount of received light depends on the hydrogen gas concentration, the hydrogen gas concentration can be detected by measuring the amount of change in the amount of received light.

FIG. 3 shows another embodiment of the invention.

In this example, as in the previous example, there are an input optical fiber 15A and an output optical fiber 1 at both ends of the optical waveguide.
5B, a reflector 18 such as an aluminum vapor-deposited film is provided in close contact with one end face of the optical waveguide 11, and an optical fiber 15 for both input and output is connected to the other end of the waveguide. The structure of is similar to that of the previous embodiment.

The structure of this example undergoes evanescent light absorption and attenuation by the light absorption layer 12 during both the reciprocating strokes of the waveguide 11, so the element can be made smaller compared to the structure of the previous example, and the detection sensitivity can be improved with the same size element. It has the advantage of being even better.

Next, specific numerical examples of the present invention will be explained.

Using LiNbO ₃ as the substrate 10, an optical waveguide 11 is formed in the substrate 10 by thermally diffusing Ti, and a light absorption layer 12 is formed on the exposed surface of the optical waveguide 11.
A WO ₃ thin film was vacuum deposited to a thickness of 1 μm.

WO ₃ was deposited using resistance heating using pellets with a purity of 99.99% using a W-wire crucible carted with alumina.

The deposition conditions were an oxygen pressure of 1×10 ⁻⁴ Torr, high-frequency power for ionization of 200 W, and ion acceleration voltage of −500 V. The obtained WO ₃ thin film was amorphous and colorless and transparent. Hydrogen adsorption layer 13 on the above WO ₃ film
Pd was deposited to a thickness of 100 angstroms by electron beam heating evaporation.

Next, a SiO ₂ film was deposited on the hydrogen adsorption layer 13 as a hydrogen selective permeation film 14 by electron beam heating evaporation. Using SiO pellets with a purity of 99.99% as a deposition source, a SiO ₂ film 14 with a thickness of 500 angstroms was obtained under conditions of an oxygen pressure of 1×10 ^-4 Torr, a high frequency power for ionization of 50 W, and an ion acceleration voltage of −500 V.

Semiconductor laser light with a wavelength of 1.3 μm was introduced through the optical fiber connected to the waveguide 11 of the sensor element created as described above, and the output light amount was measured with a photodetector connected to the end of the optical fiber on the output side. Approximately ±5% hydrogen gas concentration range from 10 to 2000 ppm
It was possible to measure with an accuracy of

Further, when the hydrogen gas concentration was measured after the sensor element was left at a temperature of 50° C. and a humidity of 90% for 6 months, almost no deterioration in the detection characteristics was observed. On the other hand, when the conventional sensor element without the protective coating 14 was subjected to the above environmental test and the hydrogen gas concentration was measured, a significant decrease in the detection characteristics was observed.

〔Effect of the invention〕

According to the present invention, since the hydrogen gas adsorption layer is protectively coated with a hydrogen selectively permeable coating, hydrogen gas, which is the object to be detected, can freely contact the adsorption layer of the sensor as in the past, and at the same time The permeation of other components, especially water vapor, which adversely affect the reaction of the light absorption layer is prevented, and therefore stable hydrogen detection performance can be maintained over a long period of time.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view showing one embodiment of the present invention, Fig. 2 is a plan view of the same, Fig. 3 is a side sectional view showing another embodiment of the invention, and Fig. 4 is a conventional optical sensor. FIG. 10... Substrate, 11... Optical waveguide, 12... Light absorption layer, 13... Hydrogen adsorption layer, 14... Hydrogen selectively permeable protective coating, 15, 15A, 15B... Optical fiber, 16... Light source device , 17... photodetector,
18...Reflector.

Claims (1)

[Claims] 1. A dielectric film whose light absorption coefficient changes due to reaction with hydrogen is provided in contact with the optical waveguide, and a metal film that dissociates and adsorbs hydrogen gas is provided on the film, so that the light emitted from the waveguide is A hydrogen detection optical sensor configured to detect hydrogen based on changes in the amount of light, characterized in that the surface of the metal film is protectively coated with a selectively permeable coating that is permeable to hydrogen gas and impermeable to at least water vapor. Detection light sensor. 2. The hydrogen detection optical sensor according to claim 1, wherein the selective transmission film is a vapor deposited film of SiO ₂ .