JPS61186836A - Liquid sensor - Google Patents

Abstract

PURPOSE:To detect the sticking of liquid to be detected to a coating layer with high reliability by providing a single-mode light guide on a light- transmissive substrate and providing the coating layer that the object liquid immerse thereupon, and thus constituting a sensor. CONSTITUTION:The single-mode light guide 3 is provided on the substrate 2 made of quartz glass, etc., and the coating layer 4 is provided thereupon. The coating layer is formed of the material, such as silicone resin and a porous material, that the liquid to be detected immerses. The refractive index of the light guide 3 is made larger than that of the substrate 2 and the refractive index of the coating layer 3 is made smaller than that of the light guide 3. Further, optical fibers 5A and 5B are connected to both sides of the light guide 3 of this detector 1. When oil which is large in refractive index sticks on the coating layer 4, the oil oozes to the light guide 3 and the ratio of an evanescent wave 7 increases, so that projection light from the optical fiber guide, so an oil leak in a plant, etc., is detected with high reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a liquid sensor that optically senses liquid such as oil.

[Description of prior art]

Recently, oil leak accidents have been occurring frequently at oil storage bases, petrochemical plants, etc., and highly reliable detectors are required in accordance with legal regulations for early detection of such accidents. The sensor must also be highly safe.

Conventionally, polymer lactate fibers have been known as optical liquid sensors. This polymer clad optical fiber has a core made of quartz and a refractive index. Light entering the optical fiber from the quartz end is repeatedly totally reflected at the interface between the core and the cladding, and propagates to the other end with low loss.

However, when oil with a high refractive index adheres to the optical fiber and infiltrates into the cladding, the refractive index of the cladding increases.

As a result, some light that enters the optical fiber is refracted and exits the core without being totally reflected at the interface between the core and the cladding.

For this reason, the amount of light that propagates through the light 7 eyelid while being totally reflected is reduced compared to before oil infiltration.

Therefore, oil leakage can be detected by placing a light source at one end of the optical fiber and a light receiver at the other end and monitoring changes in the amount of propagated light.

[Problems with conventional technology]

In the conventional polymer clad fiber described above, the diameter of the fiber is very small, so oil leakage cannot be detected unless the optical fiber is precisely positioned at the location where oil leakage occurs.

In other words, with optical fibers, oil leaks can only be detected in a linear manner, so oil leaks can be overlooked! A highly reliable sensor with a high probability is a means to solve the problem of Q, 1% (j)0. A coating layer made of a substance into which the sensing liquid can permeate, such as silicone resin, or an inorganic or organic porous material having open cells, is provided to cover this waveguide.

When using a material with a relatively high refractive index such as multi-component glass as a substrate, the coating layer should be removed in order to increase the leakage of evaporative waves from the waveguide to the coating layer when the detection liquid infiltrates the coating layer. A thin intermediate layer having a refractive index smaller than that of the waveguide and larger than that of the coating layer may be provided between the waveguide and the waveguide.

Such an intermediate layer needs to have a thickness that does not interfere with evanescent wave coupling between the coating layer and the waveguide, and is generally about 3/3 of the thickness of a single mode optical waveguide or less. is desirable.

[For production]

If the sensor coating layer has a refractive index higher than this coating layer)! !
: As a result, of the light propagating in the single mode optical waveguide,
The proportion of evanescent waves that seep into the coating layer increases, the amount of light absorbed by the coating layer increases, and the amount of light received decreases.

The presence of a detection liquid, such as an oil leak, at the location where the sensor is installed can be detected with high sensitivity by the above-mentioned change in the amount of received light.

〔Example〕

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

In FIG. 1, / is a sensor, and the sensor l is made of a transparent material such as quartz glass (refraction example n1-8≠j) on the surface of a substrate having a larger refractive index than the substrate 2, e.g. A single mode optical waveguide 3 made of a transparent thin film with a refractive index n2-≠B is provided. The thickness of this single mode optical waveguide 3 is, for example, 5 μm.

Further, a coating layer is provided to cover the upper surface of this single mode optical waveguide 3. This coating layer is made of a material and has a thickness that allows the attached liquid to be detected, such as oil, to easily infiltrate in the thickness direction, and its refractive index n3 is smaller than the refractive index n2 of the single mode optical waveguide 3. is necessary.

Ru. Single mode optical fibers jA and jB are respectively coupled to opposite end surfaces of the sensor having the above structure, and the single mode light is made to enter the waveguide 3 through one optical fiber jA,
Further, after the light emitted from the waveguide 3 is received by the fiber jB, it is guided to a light receiver (not shown) and the change in the received light f is measured.

In the above device, when the liquid 6 to be detected adheres to the surface of the WIt layer 6 to be detected, this liquid 6 quickly infiltrates into the coating layer q,
As a result, the refractive index n3 of the coating layer increases.

For example, if the liquid to be detected 6 is oil with a refractive index of /4Z5g and the coating layer ψ is made of silicone resin with a refractive index of 0, the refractive index n3 of the coating layer increases to about tI3/.

As a result, the proportion of evanescent waves 7 that seep into the coating layer 4 from the single mode light passing through the waveguide 3 increases, the proportion of light absorbed by the coating layer increases, and Since the amount of emitted light is reduced, it is possible to detect the appearance of a liquid to be detected, such as an oil leak.

FIG. 2 shows another embodiment of the invention.

Even if the index difference becomes relatively large and the refractive index of the coating layer increases due to infiltration of the liquid to be detected, the leakage of evanescent waves to the coating layer is insufficient, making it impossible to obtain high detection sensitivity. Therefore, in the structure of this example, an intermediate layer made of a material having a refractive index n4 between the two is provided between the single mode optical waveguide 3 and the y-layer t.

If the thickness of this intermediate layer is too large, the seepage of evanescent waves from the waveguide 3 to the covering layer will be blocked.
It is desirable to set it to less than 1/min. - As an example, a multi-component glass with a refractive index of 85j is used for the substrate λ, and the refractive index j! A single mode optical waveguide 3 having a thickness of approximately tμm and a refractive index of 8j5 is laminated on the waveguide 3 as an intermediate layer g. Then, a coating layer made of, for example, silicone resin is provided on this intermediate layer.

The appearance of a known liquid can be detected.

In addition, when multi-component glass, quartz glass, or plastic is used as the material of the substrate 2, the two-stage electric field ion exchange method, the flame hydrolysis method used in the production of Hikari 7 Aiper, etc., or the Optical waveguides can be formed by using well-known techniques such as photopolymerization. The refractive index distribution in the vertical cross section of this optical waveguide may be uniform or may have a slope. In addition to the above, the optical waveguide can be formed by vapor deposition,
There is no problem even if it is formed by a method such as sputtering, ion implantation, or thermal diffusion.

If the above-mentioned sensor is constructed of multi-component glass or quartz glass, and no coating layer ψ is provided near the input end and output end of the waveguide 30, the optical fiber 5A,
Even if a glass optical fiber with low transmission loss is used as tB, the optical 7-inode and the substrate can be easily connected by fusion bonding or the like. Moreover, the single mode optical waveguide 3 in the illustrated example is 2,? effect can be obtained. Also Hikari 7 Aino<! ;A.

Figure 3 in the box above shows a device for actually detecting oil leakage using a prism coupler, lenses, etc. without using i'B. First, sensors 1 are placed at locations in the oil tank 10 where oil leakage is likely to occur, and these sensors are connected in series or in parallel using optical fibers 1. The light from the light source /2 is input to the light 7 Aiper/l at the farthest end, and the light emitted from the optical fiber // at the other end is detected by the photodetector 13. Then, the electrical signal from the photodetector /3 is guided to the alarm /6 via the amplifier l≠ and the comparator 93/j.

Note that by using the backscattering method, which is used to measure the connection loss of optical fiber connectors and the transmission loss of optical fibers, it is possible not only to simply detect oil leaks, but also to know the location of oil leaks.

In the above description, the sensing of oil has been described, but any liquid that infiltrates the coating layer 1 and increases the refractive index of the coating layer 1 can be sensed without being limited to oil.

〔Effect of the invention〕

Since the liquid sensor according to the present invention uses a flat plate waveguide, the coating layer in which the liquid is permeated can be provided over a wider range than the optical waveguide 3 in the conventional polymer clad fiber type sensor. Also, the detection area can be increased to the extent of light.

Furthermore, it is easier to replace than conventional fibers constructed of continuous fibers.

In addition, in order to detect changes in the amount of evanescent waves seeping out from a single mode optical waveguide, processing is required to control the incident angle of light into the waveguide within a fixed angle range, as in the case of using a multimode optical waveguide. It is easy to manufacture as there is no need for it.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, FIG. 1 is a cross-sectional view showing another embodiment of the present invention, and FIG. 3 is a cross-sectional view showing an example in which the sensor of the present invention is applied to oil leak detection. It is a schematic diagram.

Claims (1)

[Claims] A transparent substrate, a single mode optical waveguide formed on the substrate, and a coating layer made of a substance that can be infiltrated by a sensing liquid and laminated on the optical waveguide with or without an intermediate thin film. A liquid sensor characterized by being equipped with.