JPS62170840A - Optical sensor for detecting hydrogen - Google Patents

Abstract

PURPOSE:To maintain hydrogen detecting performance stably for a long period of time by coating the entire surface of an adsorptive layer with a selective permeable membrane which allows the permeation of gaseous hydrogen and does not allow the permeation of. CONSTITUTION:LiNbO3 is used as a substrate 10 and Ti is thermally diffused therein to form an optical waveguide 11 in the substrate 10. A thin WO3 film is formed by vacuum deposition to about 1mum thickness as an absorptive layer 12 on the exposed surface of the waveguide 11. Pd is stuck by a vapor deposition method using electron ray heating to about 100Angstrom thickness as the hydrogen adsorptive layer 13 on the WO3 film. An SiO2 film is stuck by the vapor deposition method using electron ray heating as the hydrogen selective permeable membrane 14 on the hydrogen adsorptive layer 13. Semiconductor laser light of 1.3Xm wavelength is made incident on the waveguide 11 of such sensor element through an optical fiber connected to said waveguide and the quantity of the output light is measured by a detector 17, by which the concn. of 10-2,000ppm gaseous hydrogen is measured with + or -5% accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an essentially snow-proof type optical sensor that detects hydrogen gas concentration using an all-light 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 l,
A light absorption layer 3 made of a substance whose light absorption coefficient changes when reacting with hydrogen is provided on the exposed upper surface of this optical waveguide, and an adsorption layer 3 made of a metal film that dissociates and adsorbs hydrogen gas is further provided on the top of this light absorption layer 3. Layer l is laminated. An input optical fiber 1 and an output optical fiber 5B are connected to both ends of the optical waveguide.

□ When the light absorption coefficient of the light@acid layer 3 increases due to contact, the evanescent light is absorbed and attenuated, and the output sight to the output optical fiber, tB, decreases.

Therefore, by measuring the change in the amount of light emitted from the output light 7 eyeball and ltB, it is possible to know the hydrogen gas concentration.
Gate.

[Problem that the invention seeks to solve]

In the conventional structure described above, the surface of the hydrogen gas adsorption layer t is in constant contact with the outside air, and therefore is susceptible to reactions with various substances other than hydrogen gas, and in particular reacts with water vapor, causing the adsorption layer 1 and light There was a problem in that the reactivity of the absorption layer 3 to hydrogen gas deteriorated early.

[Means for solving problems]

The entire surface of the adsorbed N'l was coated with a selectively permeable coating that was permeable to hydrogen gas and impermeable to at least water vapor.

[For production]

Hydrogen gas passes through the selectively permeable membrane, is dissociated and adsorbed in the hydrogen gas adsorption layer as in the past, and the light gIk of the light absorption layer that reacts with the dissociated hydrogen becomes a differential coefficient, and the amount of light emitted from the optical waveguide changes. do.

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 and protected, so that stable nitrogen detection performance is maintained over a long period of time.

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

In Figures 1 and 2, 10 is a substrate, /l is an optical waveguide, and the waveguide // is formed by, for example, thermal diffusion of Ti into a LiNbO3 substrate or ion exchange diffusion into a glass substrate. be done.

Then, a light absorption layer /,
2 are laminated, and an adsorption layer/3 is further laminated on the light absorption layer/2.

The adsorption layer/3 consists of a metal thin film that adsorbs and dissociates hydrogen gas to generate electrons and protons, and the light absorption layer/2 consists of a dielectric thin film whose light absorption coefficient changes in response to the electrons and protons mentioned above. has been done.

Palladium (Pd) or platinum (Pt) is suitable as the material for the adsorption layer/3.

In addition, WO3 is suitable as a material for forming the light absorption layer/2, and other inorganic materials that generally exhibit electrochromic properties, such as EVA M003+V2O5, TiO2゜Ir(O
H)n, Rh203XH20, etc. can be used.

Further, the light absorption layer 12 may be composed of an organic material, such as Ehaheb Elviologen, Shea/Phenylviologen,
Cobalt pyridyl complexes, polymerized tetrathiofulvalene (TTF), lutetium siphthalocyanine, and the like can be used. The adsorption layer 13 is made of a thin film made of a material with excellent weather resistance, such as a 5102 film, having micropores that are capable of blocking at least water vapor transmission.

As an example, an electron beam heating evaporation method is used, high purity SiO pellets are used as the evaporation source, oxygen pressure/X1O-4Torr,
High frequency power for ionization 50W, ion acceleration voltage -5oo
By depositing a 5i02 film with a thickness of about 500 angstroms under the conditions of v, a film/l having the above function can be obtained. In addition to 5i02, zeolite, alumina, etc. are also coated/
The film /g may be formed only in the area where the adsorption layer /3 and the light absorption layer /2 are formed, but it may be formed over the entire length of the optical waveguide // as shown in the example. This is convenient because it also protects the waveguide /l.

In the above case, both layers/2, the coating part in the area outside 13/
i requires selective hydrogen permeability as described above, and it is desirable to smooth it in order to reduce propagation loss.

Optical waveguide of sensor element 20 configured as described above//
Connect the input optical fiber /jA to one end of the input optical fiber 1, and connect the input optical fiber 1 to the light source device such as a semiconductor laser located at
Connect the other end of 5A and connect the output optical fiber/j
Connect the other end of B to photodetector/7. The light emitted from the light source device/B is transmitted through the optical fiber/S'A, enters the optical waveguide // of the sensor element 20, and propagates through the waveguide //.

A part of the propagated light leaks into the light absorption layer/2 as evanescent light. The amount of this evanescent light seeping out depends on the refractive index of the light absorption layer /2 and the refractive index of the waveguide //, and can be increased to about 20%. When hydrogen gas is present at the N location of the sensor element 20,
Hydrogen gas passes through the protective coating /II, contacts the adsorption layer /3, for example, a Pd thin film, and is dissociated and adsorbed, and this dissociated hydrogen reacts with the light absorption layer /2 to absorb light in the absorption layer /2. The coefficient changes.

For example, when the light absorption layer/2 is made of WO3, tungsten bronze is produced and colored.

As a result, the evanescent light of the guided light propagating through the optical waveguide // is absorbed and attenuated in the WO3 layer, and the amount of light received by the photodetector /7 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.

Optical fiber for human power/jA and optical fiber for output 75B,
Instead of connecting =, one end face of the optical waveguide //
11, a reflector such as an aluminum vapor-deposited film is provided in close contact with the
An optical fiber 2□15 for both input and output is connected to the other end of the waveguide, and the other structure is the same as that of the previous embodiment.

The structure of this example undergoes evanescent light absorption attenuation by the light absorption layer 2 during both the round trip of the waveguide //, so the element can be made smaller compared to the structure of the previous example, and the detection sensitivity can be increased with the same size element. This has the advantage of further improving.

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

Using LiNbO3 as the substrate 10, T1 is thermally diffused to form an optical waveguide // in the substrate lO.
A 7μ thin film of WO3 is placed as a light absorption layer 7.2 on the exposed surface of the
It was vacuum deposited to a thickness of m.

WO3 was deposited using resistance heating using pellets with a purity of 99.99% using a W-wire crucible coated with alumina.

The deposition conditions were oxygen pressure/X1O-4 TOrr, ionization high frequency power of 200 W, and ion acceleration voltage=soov thermal evaporation method.

Next, on this hydrogen adsorption layer/3, a 5102 film was deposited as a hydrogen selective permeation film/l by an electron beam heating vapor deposition method. Using a 99.99% pure 5J-0 beret as a deposition source, the film thickness was determined under the conditions of oxygen pressure/X1O-4 TOrr, ionization high frequency power of 50 W, and ion acceleration voltage of -5oov.
A film of 8102 O angstroms/ge was obtained.

Semiconductor laser light with a wavelength of 3 μm is incident on the optical fiber connected to the waveguide // of the sensor element created as described above, and the output light amount is measured by the photodetector connected to the end of the optical fiber on the output side. When measured, it was 70~. ! ooopp
It was possible to measure a hydrogen gas concentration range of m with an accuracy of approximately ±S%.

Further, when the hydrogen gas concentration was measured after the sensor element was left for 6 months at a temperature of SO DEG C. and a humidity of 90%, almost no deterioration in the detection characteristics was observed.

On the other hand, when the conventional sensor element without the protective film/II was subjected to the above environmental test and the hydrogen gas concentration was measured, a significant decrease in the detection characteristics was observed.

[Effects of the Invention] According to the present invention, since the hydrogen gas adsorption layer is coated with a hydrogen selectively permeable film, hydrogen gas, which is the object to be detected, can freely contact the adsorption layer of the sensor as before. At the same time, the permeation of other components, particularly water vapor, which adversely affect the reaction of the adsorption layer and the light absorption layer is prevented, and therefore stable hydrogen detection performance can be maintained over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a side sectional view showing one embodiment of the present invention, FIG. 2 is a plan view thereof, and FIG. 3 is a side sectional view showing another embodiment of the present invention.
FIG. 1 is a side sectional view showing a conventional optical sensor. 10...Substrate //...Optical waveguide/,!・・・
...Light absorption layer /3...Hydrogen adsorption layer /lI...
・Hydrogen selectively permeable protective film/! ;,/! ;A,,/3;
B...Hikari 7 Aiba/Otsu...Light source device/7
...Photodetector/r...Reflector Patent applicant Todoroki Director, Agency of Industrial Science and Technology Figure 1'm2

Claims (2)

[Claims] (1) Provide a dielectric film in contact with the optical waveguide whose light absorption coefficient changes due to reaction with hydrogen, and provide a metal film on the film that dissociates and adsorbs hydrogen gas, so that hydrogen gas can be absorbed by changing the amount of light emitted from the waveguide. A hydrogen detection optical sensor configured to detect hydrogen, 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. (2) The hydrogen detection optical sensor according to claim 1, wherein the selective transmission film is a vapor deposited film of SiO_2.