JPS6329236A - Gas detecting optical sensor - Google Patents

Abstract

PURPOSE:To improve the detection sensitivity of a photosensor by forming a transmissivity changing optical waveguide part to be provided adjacently to a thin metallic film for dissociating and adsorbing a contact gaseous substrate in such a manner that the refractive index is lower in the outside part thereof in contact with a gas adsorptive layer than in the inside part thereof. CONSTITUTION:A thin film-like single mode optical waveguide 11 is provided on the surface of a transparent dielectric substrate 10. The transmissivity changing optical waveguide part 12 is laminated and formed to a partial region atop the waveguide 11 and further, the gas adsorptive layer 13 is laminated and formed on the waveguide layer 12. The adsorptive layer 13 consists of the thin metallic film for dissocilating and adsorbing gaseous hydrogen and the waveguide layer 12 consists of a material which can change the coefft. of light absorption by reacting with the adsorbed gas. Said layer increases the coefft. of light absorption by bonding to hydrogen. The waveguide layer 12 is constituted of two layers; an upper layer part 12A in contact with the adsorptive layer 13 and a lower layer part 12B. These layers are formed to the have the refractive index lower in the part 12A than in the part 12B. Light of a light source 16 is supplied from an optical fiber 14 for input to one end of the waveguide 11 and a photodetector 17 is connected through an optical fiber for output to the other end. The optical sensor having the improved detection sensitivity is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an essentially explosion-proof optical sensor that detects gas concentration using an all-light method, and particularly to an optical sensor that is used for detecting hydrogen gas.

[Prior art]

As an all-optical, essentially explosion-proof type hydrogen gas optical sensor, one having the structure shown in Figure 1 is conventionally known.

In the figure, / is a transparent dielectric substrate such as LiNbO3, 2
3 is a single mode optical waveguide provided on the surface of this substrate; 3 is a variable transmittance optical waveguide layer partially formed on the optical waveguide 2;
l is a gas adsorption layer provided on the same layer 3, and the optical waveguide 20
A single-mode input optical fiber 5 and an output optical fiber 6 are connected to both ends, respectively.

The gas adsorption layer ψ is made of a metal thin film, for example, Pd, which dissociates and adsorbs hydrogen scum, and the transmittance changing optical waveguide layer 3 is made of a transparent dielectric whose light absorption coefficient changes by reacting with the hydrogen gas adsorbed in the layer. A thin film of, for example, WO2.

In the above sensor, light emitted from a remote light source and transmitted through the input optical fiber 5 propagates through the waveguide, and part of the propagated light passes through the transmittance change waveguide layer 3 and is used for output. Emitted to optical fiber B.

When hydrogen gas exists near the sensor, the hydrogen gas that has come into contact with the gas adsorption layer q is dissociated and adsorbed, and as a result of reacting with this adsorbed gas, the optical absorption coefficient of the waveguide layer 3 changes in proportion to the concentration of hydrogen gas. However, the amount of light emitted from the waveguide changes accordingly.

Therefore, if the amount of light emitted from the waveguide 2 is constantly monitored by a photodetector connected to the other end of the output optical fiber B, it is possible to detect the concentration of hydrogen gas near the sensor from changes in the amount of received light. can.

[Problem that the invention seeks to solve]

As shown in Figure S, the refractive index of each part in the conventional hydrogen gas center is distributed such that the substrate has the lowest index, the waveguide 2 has a higher refractive index, and the transmittance change waveguide layer 3 has an even higher refractive index. have.

As shown in the figure, the power distribution 7 of the propagating light in the part where the 6-pass rate change waveguide layer 3 is provided has a maximum power in both optical waveguides! , 3, and has a distribution that gradually decreases in the vertical direction. In the upper part, a part of the propagating light will be caught by the gas-adsorbing metal thin film tlVc, and for this reason, a part of the propagating light will be absorbed by the metal thin film, resulting in poor light propagation efficiency even in a blank state without hydrogen gas. However, there was a problem in that the detection sensitivity of the sensor could not be made very high.

[Means to solve conventional problems]

The gas detection optical sensor of the present invention that solves the above problems consists of a metal thin film that dissociates and adsorbs a contact gas, and a transmittance that is provided adjacent to the metal film and whose light absorption coefficient changes due to reaction with the dissociated gas. In the gas detection sensor having a variable light waveguide, the outer portion of the variable transmittance light waveguide that is in contact with the gas adsorption layer has a lower refractive index than the inner portion.

In the present invention, the transmittance changing optical waveguide section may be provided overlapping the optical waveguide to which the optical fiber is connected and whose optical transmittance does not change due to reaction with gas, or alternatively, the transmittance changing optical waveguide section may be provided over the optical waveguide section to which the optical fiber is connected and whose optical transmittance does not change due to reaction with gas, or alternatively, the transmittance changing optical waveguide section may be provided over the optical waveguide section to which the optical fiber is connected and whose optical transmittance does not change due to reaction with gas. The transmittance-changing optical waveguide may be formed of a substance whose light absorption coefficient changes upon reaction with a dissociated gas.

[For production]

In the sensor with the above structure, the power distribution of the single mode light propagating through the transmittance change waveguide is concentrated in the high refractive index region, so the end of the power distribution slightly enters the low refractive index region, but it is not The end is located in the area and does not penetrate into the metal thin film.

For this reason, all of the propagating light propagates through the waveguide without being absorbed by the gas-adsorbing metal thin film, and therefore the amount of transmitted light in a blank state without coloring due to reaction with gas increases, which increases the detection sensitivity of the sensor. increases. Furthermore, since the thickness of the optical waveguide can be the same as before, the advantages of using single mode light will not be lost.

〔Example〕

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

In FIG. 7, 70 is a transparent current-visitor, for example LiNb.
A thin film-like single mode optical waveguide // is provided on the surface of the substrate 10 by thermal diffusion of T1.

A variable transmittance optical waveguide layer /2 is laminated on a partial region of the upper surface of the optical waveguide //, and a gas adsorption layer /3 is further laminated on this optical waveguide layer /2.

The gas adsorption layer/3 is made of a metal thin film such as Pd that dissociates and adsorbs hydrogen gas, and the optical waveguide layer/2 is made of a material whose optical absorption coefficient can change by reacting with the adsorbed gas, for example WO.
Consists of 3. WO3 combines with hydrogen to form tungsten bronze, increasing the light absorption coefficient.

The optical waveguide layer /2 is the upper layer portion in contact with the gas adsorption layer /3 /,! It is composed of two layers: A and a lower layer part /2B below this, and the refractive index of the upper layer part /2A is lower than that of the lower layer part /2B. An input optical fiber/ge is connected to one end of the optical waveguide // integrally formed on the substrate, and an output optical fiber/S is connected to the other end. The other end of the input optical fiber /+ is connected to a light source /6 located away from the sensor, and the other end of the output optical fiber /j is connected to a light receiving detector /7.

In the above sensor, after being transmitted through the input optical fiber /47, it enters the substrate waveguide //, propagates through this waveguide // and reaches the area where the transmittance change waveguide layer /2 is provided. , a part of the propagating light propagates through the waveguide layer/2.

At this time, the power distribution of the propagating light in the cross section is mostly concentrated in the high refraction portion 7.2B of the waveguide layer 2, as shown in Figure 2, and the power distribution is low near the ends. Refractive index part/
The distribution falls into 2A.

In other words, the edge of the propagating light power distribution, which conventionally entered the metal thin film /3 forming the gas adsorption layer, is
It is located within the low refractive index portion /2A of 2, and does not reach the metal thin film /3.

And since the above part /2A is transparent when there is no reaction with gas, a part of the propagating light is not absorbed by the metal thin film even when there is no reaction with gas as in the conventional case.
High propagation efficiency can be obtained.

Therefore, the amount of received light increases under the same usage conditions as before, and the detection sensitivity of the sensor improves accordingly.

In the embodiment described above, the optical waveguide region of the sensor has a laminated structure of an optical waveguide l/2 whose transmittance does not change, which is integrally formed on the substrate, and a waveguide layer /2 whose light absorption coefficient changes due to reaction with a gas. However, it is also possible to use a waveguide with a single structure as shown in FIG.

That is, in the example shown in FIG. 3, a ridge-shaped waveguide 2 made of a substance whose light absorption coefficient changes upon reaction with a dissociated gas is formed on a transparent dielectric substrate 10 such as a glass plate, and
A structure in which the constant thickness part /, 2A on the outer surface side of this waveguide / 2 has a low refractive index, the inside / 2B has a high refractive index, and the exposed surface of the waveguide / 2 is covered with a gas dissociation and adsorption metal thin film / 3. An input optical fiber and an output optical fiber are connected to both ends of the waveguides 2 and 2, respectively.

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

〔Concrete example〕

Using I, 1Nbo3 as the substrate 10, T1 was changed to LiNb by heat treatment at 7000°C for 1/2 hour in an oxygen atmosphere.
It was diffused into the O3 substrate to form an optical waveguide // integrated with the substrate.

Polycrystalline Wo, 3 is placed on this waveguide as a high refractive index portion /2B of the transmittance change waveguide layer /2.
It was vacuum deposited to a thickness of m. For Wo3, pellets with a purity of 99.99% were used and resistance heating vapor deposition was performed using an alumina-coated W wire crucible.

The vapor deposition condition is oxygen pressure! ;×10-4 Torr, high frequency power for ionization q 200W, ion acceleration voltage -5
oov.

The substrate temperature is 300″C, and the refractive index of colorless and transparent material is 2.2.
A polycrystalline WO3 film of No. 2 was obtained.

On top of this film is a low refractive index part /, 2A with a refractive index of 2, /
Amorphous Wo3 was vacuum-deposited to a thickness of O,OSμm.

The deposition conditions were the same as the polycrystalline W described above except that the substrate temperature was room temperature.
It was the same as when forming the O3 film. Furthermore, the above amorphous WO3
On film/2A, Pd was deposited as gas adsorption layer/3 to a thickness of 700A by electron beam heating evaporation.

The input optical fiber /1 and the output optical fiber 15 were connected to this so that the coupling efficiency was maximized. Place the sensor unit in the atmosphere to be detected, input a source light with a wavelength of 3 μm from one end of the input optical fiber /L, and place a photodetector at the other end of the output optical fiber /S to measure the output light amount. was measured.

As a result of experiments, it was confirmed that it was possible to measure a hydrogen gas concentration range of 10 to 2000 ppm with an accuracy of ±2%.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, FIG. 2 is a diagram showing the refractive index distribution and propagation light power distribution in the sensor of the present invention, and FIG. 3 is a cross-sectional view showing another embodiment of the present invention. Figure q is a sectional view showing a conventional hydrogen gas detection optical sensor, and Figure S is a diagram showing the refractive index distribution and propagation light power distribution of the conventional product. 10... Substrate //... Optical waveguide /2... Transmittance change optical waveguide layer /2A low refractive index part
/2B-...High refractive index part/3 Gas adsorption layer /<Z
, /3 Optical fiber /6...Light source /7 Light receiver/Propagating light power distribution

Claims (1)

[Claims] A gas detection sensor comprising a metal thin film that dissociates and adsorbs a contact gas, and a transmittance-changing optical waveguide section that is provided adjacent to the film and whose light absorption coefficient changes due to reaction with the adsorbed gas. A gas detection optical sensor characterized in that the outer part of the optical waveguide in contact with the gas adsorption layer has a lower refractive index than the inner part.