JPH02171629A - Light waveguide type temperature sensor - Google Patents

Abstract

PURPOSE:To obtain a simple and small temperature sensor by providing a prism inside a core with a rate of dependence on temperature of refractive index differing from the core. CONSTITUTION:A prism 3 made of a material with a rate of dependence on temperature of refractive index less than that of a core 1, for example, optical glass, is provided inside the core 1 comprising an optical resin. Light beam incident into the core 1 at an angle smaller than a transmission critical angle travels straight through the core 1 and moves being totally reflected on an boundary plane between the core 1 and a clad 2. Transmission of light reaches the maximum thereof at a temperature with a refractive index of the core 1 equaling that of the prism 3. As an ambient temperature rises, the refractive index of the prism 3 becomes less than that of the core 1 and the light beam refracted at an incident side end face 3a exceeds the propagation critical angle to be leaked to the clad 2 so that transmission thereof decreases. Thus, the detection of a quantity of light with a photo detector 5 enables measurement of a change in temperature, thereby producing a simple and small temperature sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a temperature sensor using an optical waveguide.

[Conventional technology]

Conventionally, as a temperature sensor using light, JP-A-62-92
Some of them are disclosed in Japanese Patent Publication No. 40 and Japanese Patent Application Laid-Open No. 62-55532. Both of these utilize optical fibers, and the former has a cladding layer made of a material whose refractive index changes greatly depending on the temperature on the outer periphery of the optical fiber core, and the refraction of the cladding layer due to temperature changes. The temperature is determined by optically detecting the change in the propagation mode of the optical fiber caused by the rate change. The latter involves inserting an object between the end faces of a pair of opposing optical fibers, the refractive index of which is approximately equal to the refractive index of the optical fiber, and the temperature coefficient of the refractive index different from the temperature coefficient of the refractive index of the optical fiber. The ambient temperature is measured by measuring the change in the intensity of the optical power reflected at the boundary.

[Problem to be solved by the invention]

However, in the above conventional example, since an optical fiber is used as the temperature sensor, a jig and a coupling optical system are separately required for aligning the optical axis with the light emitting element and the light receiving element. There are problems in that the overall configuration becomes complicated and the cost becomes high.

The present invention has been made in view of the above points, and its object is to provide a simple, compact, and low-cost leading waveform temperature sensor. Another object of the present invention is to provide an optical waveguide trace temperature sensor with less variation in characteristics.

[Means to solve the problem]

The optical waveguide trace temperature sensor of the present invention includes a prism having a temperature dependence rate of refractive index different from that of the core, inside the core of the optical waveguide consisting of a central core and a cladding formed on the outer periphery of the core. The present invention is characterized in that a ball lens is used in place of the prism.

[Effect]

When the light passing through the core of the optical waveguide changes from the normal temperature, the prism is made of a material whose refractive index has a different temperature dependence rate from that of the core. If is smaller than the temperature dependence of the refractive index of the core, it will cause a larger change in the refractive index than the core, so
The light beam propagating inside the core is refracted at the entrance side end face of the prism, and further refracted at the exit side end face. However,
The angles of the incident end face and the exit end face are different, and the light rays emitted from the prism to the core do not have the same incident angle as the previous light ray, but exceed the critical angle at the boundary between the core and the cladding. Put it away. As a result, the amount of light rays propagating inside the core is reduced.

[Example] Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a perspective view of an optical waveguide trace temperature sensor showing an embodiment of the present invention. Reference numeral 1 denotes a core made of an optical plastic material such as PMMA, through which light rays pass. A cladding 2 covers the core 1.

Reference numeral 3 denotes a prism made of optical glass or the like formed inside the core 1, and is made of a material whose temperature dependence of refractive index is smaller than that of the core. FIG. 2 shows a graph showing the temperature dependence of the refractive index of the optical plastic and optical glass. The temperature dependent coefficient of optical plastic is 1.0 to 1.
．． The temperature dependent coefficient of 2X10-'/'C1 optical glass is:
2.0 to 52 X 10-'/''C.Furthermore, the entrance side end surface 3a of the prism 3, on which the light beam propagating inside the core 1 enters, is not parallel to the exit side end surface 3b. , is tilted.

Note that the prism 3 may be made of a material whose temperature dependence of refractive index is larger than that of the core 1.

In other words, it is sufficient that the temperature dependence rates of the refractive indexes of the two materials are different.

Further, the entrance side end surface 3b of the prism 3 may be tilted. In other words, it is sufficient to prevent the incident side end face 3a and the output side end face 3b from being parallel to each other.

4 is a light source consisting of an LED or LD, and light emitted from the light source 4 is incident on the core 1 of the optical waveguide. Reference numeral 5 denotes a light receiving element made of a PD or the like, which receives the light propagated within the core 1 of the leading waveguide. 6 is a heat insulating layer, and the prism 3 of the optical waveguide
It is installed to cover areas other than the surrounding area. this is,
This is to suppress temperature changes in the cladding 2 and to prevent changes in the critical propagation angle of light rays propagating within the core 1.

Next, the operation of this embodiment will be explained.

The refractive index of core 1, cladding 2, and prism 3 is n
+ % nz % ni, then in a normal leading wavepath, n, > n, and if the critical angle of propagation 11 is θ, then θ@, =co s-' (nz /n+)
becomes. A light beam incident at an angle smaller than the propagation critical angle θ travels straight in the core 1 and is totally reflected at the interface between the core 1 and the cladding 2.

Now, if n,=n at the reference temperature T0, as shown in FIG. 3, regardless of the presence of the prism 3, the propagation critical angle θ
Since the light ray R incident at a smaller angle θ passes through the core 1, the amount of light transmitted is the largest in this state.

The temperature around where the optical waveguide is installed is TI(T, <T
, ), the refractive index n of the prism 3 is the core 1
is smaller than the refractive index nl.

If the angle of incidence at the inclined incident side end surface 3a of the prism 3 is θ1, then the angle θ2 at the incident side end surface 3a (θ2>θ,)
It is refracted to From Snell's law, this means that n, sin
Since θ, = n, sin θ2, 11. >n=, θ2>θ1. The incident ray R refracted at the entrance end surface 3a is refracted again at the exit end surface 3b of the prism 3, but the incident angle θ from the core 1 to the cladding 2 is
is θ, > θ, and for the ray R propagating at an angle θ close to the critical propagation angle θ, θ3 exceeds the critical propagation angle θ. As a result, the light ray R leaks to the cladding 2.

In FIG. 4, if the entrance end face of the prism 3 is parallel to the exit end face 3b as shown in 3a, the angle of incidence from the core 1 to the cladding 2 after leaving the prism 3 is:
Since the angle θ is the same as the incident angle θ before the ray R enters the prism 3, it is totally reflected at the boundary between the core 1 and the cladding 2, and the ray R is not leaked to the cladding 2.

Therefore, as the ambient temperature becomes higher than the reference temperature T0, the amount of light propagating within the optical waveguide decreases, and by detecting this amount of light with the light receiving element 5, a change in temperature can be determined.

It should be noted that if the propagation mode of light in the optical waveguide is multi-mode, temperature changes can be detected more accurately.

Further, in this embodiment, n at the reference temperature T0 is set as =i13, but since the temperature change is observed based on a change in the transmittance of the amount of light, n at the reference temperature T0 may be n, ≠n. However, if n, = n3, the amount of transmitted light at the reference temperature T0 becomes larger, and the range of change in transmittance can be increased, so that more accurate measurement is possible.

In order to remove disturbances caused by output fluctuations of the light source, the fifth
As shown in the figure, in addition to the temperature detection leading waveguide 8, a reference optical waveguide 8' is separately provided, each output is amplified by an amplifier 6, and the outputs are compared by a comparator 7. Fluctuations in light emission power due to temperature changes of the light source 4 can be corrected.

Furthermore, it goes without saying that the same effect can be obtained even if the temperature dependence of each refractive index is made to have a relationship opposite to that of the above embodiment depending on the materials of the core 1 and the prism 3. However, in this case, for example, if a temperature range of 0°C to 50°C is to be measured, it is desirable that n+ = n at 50°C.

Furthermore, in the above embodiment, instead of the prism 3,
The use of a ball lens has the effect of reducing variations in characteristics.

In the above embodiment, since an optical waveguide is used as the temperature sensor, the optical axis can be aligned by, for example, forming a lens or the like for aligning the optical axis with the light source 4 and the light receiving element 5 as an integral part of the optical waveguide. This has the effect that it can be easily performed.

〔Effect of the invention〕

As described above, according to the optical waveguide trace temperature sensor of the present invention, the temperature dependence rate of the refractive index exists inside the core of the optical waveguide, which is composed of a central core and a cladding formed on the outer periphery of the core. Since a prism different from the core was provided,
We were able to provide a simple, small, and low-cost leading waveform temperature sensor.

Furthermore, if a ball lens is used in place of the prism, an optical waveguide trace temperature sensor with even fewer variations in characteristics can be provided.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an optical waveguide showing an embodiment of the present invention, FIG. 2 is a graph for explaining the operation of the same, and FIG.
FIG. 4 is a schematic diagram for explaining the same operation as above, FIG. 5 is a block diagram showing another embodiment of the present invention. 1- Core 2... Clad 3- Prism 3a--Incidence end face 3b...Output end face 4--Light source 5--Light receiving element Patent applicant Matsushita Electric Works Co., Ltd. Agent Patent attorney Toshimaru Takemitsu (2 idiots) Figure 2 1ff Figure 3 Figure 4 Figure 5

Claims (2)

[Claims] (1) An optical waveguide comprising a central core and a cladding formed around the outer periphery of the core is provided with a prism having a temperature dependence rate of refractive index different from that of the core. Optical waveguide temperature sensor. (2) The optical waveguide type temperature sensor according to claim 1, characterized in that a ball lens is used in place of the prism.