JPS6365329A - Waveguide type temperature sensor - Google Patents

Abstract

PURPOSE:To accurately sense temperature by providing a partial section of a waveguide which has a light output side along in a partial section of a waveguide which has a light input side and a light output side across a narrow- width gap, and charging liquid in the gap. CONSTITUTION:When signal light is made incident on a main waveguide 2 from its input side B, part of the signal light in the waveguide 2 is branched to a subordinate waveguide 3. Then, the liquid charged in the gap 4 for sending varies in temperature with the external temperature, and consequently the refractive index of the light also varies, so that the quantity of the light branched from the waveguide 2 to the waveguide 3 varies. The output light intensity values of the waveguides 2 and 4 are measured and the branching ratio of the light signals is found to detect the temperature. In this case, variation in intensity due to the branching appears on both waveguides 2 and 3, so the ratio varies greatly with the temperature. Thus, the temperature is measured with high accuracy. Further, the temperature is detected from the branching ratio, so when optical fibers connected to the output sides C and D are laid on the same path, then influence of transmission loss is canceled by the ratio of the output light intensity to eliminate the influence of disturbance.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a sensor that optically measures temperature.

"Prior Art and its Problems" Some sensors that optically measure temperature include a core portion of an optical fiber filled with liquid.

This sensor uses Rayleigh scattering of the liquid that forms the core.
It takes advantage of the fact that fiber transmission loss changes with temperature, and by measuring the output intensity of the signal light propagated through the core, it is possible to detect the temperature at the location where the sensor is installed.

However, with this sensor, if the transmission loss of the optical fiber that connects the sensor to the light emitting element that emits the signal light or the detector that detects the output light intensity changes with temperature, it will directly affect the detected output light intensity. Because of this, there were complaints that highly accurate temperature measurements could not be performed.

``Means for Solving the Problems'' Therefore, in the waveguide type temperature sensor of the present invention, a narrow gap is provided in a part of the waveguide having an input side and an output side of light. The above problem was solved by providing a partial section of the waveguide having the light output side and filling the gap with liquid.

Hereinafter, the waveguide type temperature sensor of the present invention will be described in detail with reference to embodiments shown in the drawings.

FIGS. 1 and 2 show an embodiment of the present invention, and reference numeral l in the figures represents a substrate. This substrate 1 is made of silicon (Si).
), silicon dioxide (SiOz), gallium arsenide (GaA
A main waveguide 2 and a sub-waveguide 3 are formed on the surface thereof by means such as electric field ion diffusion or vapor phase growth. The waveguides 2 and 3 of the sensor in this example are formed by vapor phase growth, so
The waveguide 2.3 is provided on the substrate 1 as shown in FIG.

These waveguides 2.3 are formed from core parts 2a, 3a and cladding parts 2b, 3b.

The main waveguide 2 is a waveguide provided across the substrate 1, and its both ends are an input side B and an output side C of light. A central portion of the main waveguide 2 is provided approximately along the center line of the substrate 1. Further, both ends of the main waveguide 2 are provided apart from the center line of the substrate 1, and these ends and the above-mentioned central portion are smoothly connected in a substantially tapered shape.

The sub-waveguide 3 is provided so that one end thereof is along the center part of the main waveguide 2, and the other end extends to the same side as the output side C of the main waveguide 2 and is opened at the end surface of the substrate l. It is said that the output side is the same.

The output side of this sub-waveguide 3 is also provided at a position away from the center line of the substrate 1, and is smoothly connected to the above-mentioned one end portion in a tapered shape.

A narrow sensing gap 4 is provided between the central portion of the main waveguide 2 and one end portion of the sub-waveguide 3 adjacent thereto. The sensing gap 4 in this example is provided in the shape of a groove. The width of the sensing gap 4 is desirably set to 10 μm or less. When the width of the sensing gap 4 is 10μ or more, the loss of light passing through the sensing gap 4 becomes large.
There is a disadvantage that the measurement accuracy of the sensor is impaired. Further, the position and depth dimension of the sensing gap 4 in the depth direction are set such that at least the core portions 2a, 3a of the waveguide 2.3 are partitioned by the gap 4, that is, at least the waveguide 2.3.
It is desirable that a gap having a depth approximately the same as the height of the core portions 2a, 3a exists at a position approximately at the same depth as the core portions 2a, 3a of No. 3.

The cladding parts 2b, 3b of the waveguide 2.3 are either completely removed on both sides of the sensing gap 4, as shown in FIG. 2, or are made thinner than the other parts.

This sensing gap 4 is sealed by a housing 5, and the sealed space formed thereby is filled with liquid. As the liquid to be filled, a liquid whose refractive index changes largely depending on temperature is preferably used. Examples of such liquids include carbon tetrachloride and carbon tetrachloride diluted with hexachlorotri-butadiene.

A sensor section E is formed by the gap 8 filled with such a liquid for temperature detection, the central portion of the main waveguide 2, and one end portion of the sub-waveguide 3.

FIG. 4 shows another example of the waveguide type temperature sensor of the present invention. This sensor was manufactured by electric field ion diffusion method.

The substrate 1 of this sensor is made of a material through which light can propagate, for example S
i02, etc. This substrate 1 contains an additive that increases the refractive index by an ion diffusion method.
Germania (G eo 2) or the like is infiltrated, thereby forming a waveguide 2.3 in the substrate 1, as shown in FIG. This waveguide 2.3 consists of only a core portion, and the substrate 1 functions as a cladding.

A groove-shaped sensing gap 4 is provided between the central portion of the main waveguide 2 and one end portion of the sub-waveguide 3 provided along the main waveguide 2, and this gap 4 is closed by a lid member 6. Closed. The sealed space thus formed is filled with a liquid for temperature detection.

"Operation" Next, the operation of the waveguide type temperature sensor of the present invention will be explained.

First, when signal light enters the main waveguide 2 of the sensor of the present invention from the input side B, a part of the signal light in the main waveguide 2 is branched to the sub-waveguide 3.

When the temperature of the liquid filled in the sensing gap 4 changes due to external temperature changes, the refractive index of the liquid changes, and the amount of light branched from the main waveguide 2 to the sub-waveguide 3 changes. The temperature can be detected by measuring the intensity of the output light from the main waveguide 2 and the sub-waveguide 3 and determining the branching ratio of the signal light.

In this case, since the intensity change due to branching appears in both the main waveguide 2 and the sub waveguide 3, the ratio of these changes significantly depending on the temperature. Therefore, temperature can be measured with high precision.

In the sensor of the present invention, the temperature is detected by the ratio of the output light intensity from the main waveguide and the sub-waveguide, that is, the branching ratio, so both optical fibers connected to the output sides C and D can be connected in the same path. If installed, even if there is a change in transmission loss due to temperature changes in the optical fiber that connects this sensor to the light emitting element or detector, those effects will be canceled out by taking the ratio of the output light intensity. Ru. Therefore, the sensor of the present invention is less susceptible to disturbances.

"Example" Hereinafter, the waveguide type temperature sensor of the present invention will be described in more detail with reference to Examples.

(Example 1) A waveguide type temperature sensor having the structure shown in FIGS. 1 to 3 was created.

This waveguide type temperature sensor is made of a quartz substrate l, and the sensor part E is composed of core parts 2a and 3a of the waveguides 2 and 3.
A sensing gap 4 with a width of 5 μm is provided between them, and this sensing gap 4 is sealed by a housing 5. This sealed sensing gap 4 is filled with a temperature sensing liquid. In the sensor of this example, this liquid contains 75 vol of hexachloro 1.3 butadiene.
% and carbon tetrachloride 25vol% was used. The refractive index of this solution was 1.485 at 20°C.

A light emitting diode was connected to the input side B of the main waveguide 2 of this sensor via a 500 m long 50/125 graded index type optical fiber. In addition, on each output side C1D of the main waveguide 2 and sub waveguide 3,
An avalanche photodiode was connected via a 500 m optical fiber.

First, we set only this waveguide type temperature sensor in a constant temperature machine and investigated its temperature characteristics. The results are shown in Figure 5.

From the results shown in Fig. 5, a correspondence of 1.1 is obtained between the ratio of the output from the waveguide 2.3 (branching ratio) and the temperature, and the waveguide type temperature sensor of the present invention can be used as a temperature sensor. I was able to confirm that it is possible.

Next, in addition to this sensor, optical fibers connecting the sensor and light emitting element, and the sensor and light receiving element are set in a constant temperature machine.
When the relationship between branching ratio and temperature was investigated, the same data as the results shown in FIG. 5 were obtained. From this result, it was confirmed that the sensor of the present invention can perform stable measurements even when the temperature of the measurement environment changes.

(Example 2) A waveguide type temperature sensor was manufactured that differed from that of Example 3 only in that the sensing gap 4 was filled with carbon tetrachloride, and its temperature characteristics were investigated. The refractive index of carbon tetrachloride is 1.460 at 20°C
Met. The results are shown in Figure 6. From the results shown in FIG. 6, it was confirmed that this sensor could also be put to practical use as a temperature sensor.

"Effects of the Invention" As explained above, the waveguide temperature sensor of the present invention has the following effects:
A partial section of a sub-waveguide having an optical input end and an output side is provided along with a partial section of a sub-waveguide having an optical output side through a narrow gap, and a liquid is injected into the gap. Since the waveguide is filled, the temperature can be detected by calculating the ratio of the output light intensity from the main waveguide to the output light intensity from the sub waveguide.

In this case, since the intensity change due to branching appears in both the main waveguide and the sub waveguide, the ratio of the output light intensities from these two waveguides changes greatly with temperature. Therefore, the waveguide type temperature sensor of the present invention can sense temperature with high accuracy.

Furthermore, in the sensor of the present invention, the temperature is detected by the ratio of the output light intensity from the main waveguide and the sub-waveguide, that is, the branching ratio. Even if there are effects such as temperature on the optical fibers that connect them, those effects can be canceled out by taking the ratio of the output light intensities.

Therefore, the sensor of the present invention is less susceptible to disturbances and can accurately measure the temperature at the location where the sensor is installed.

[Brief explanation of drawings]

1 to 3 show a first embodiment of the waveguide type temperature sensor of the present invention, FIG. 1 is a plan view, and FIG.
Figure 3 is a cross-sectional view along the line ■-■ in Figure 1. Figure 4 is a cross-sectional view showing the sensor portion of the second embodiment of the waveguide type temperature sensor of the present invention. Figure 5 is a graph showing the branching ratio vs. temperature characteristics of the sensor of Example 1, and Figure 6 is the graph of Example 2.
2 is a graph showing the branching ratio versus temperature characteristic of the sensor. 2... Main waveguide, 3... Sub-waveguide, 4... Sensing gap, B... Input side, C, D... Output side.

Claims (1)

[Claims] A part of the waveguide having an input side and an output side of light is provided with a part of the waveguide having an output side of light through a narrow gap, and a liquid is further provided in the gap. A waveguide type temperature sensor characterized by being filled.