JPS6039794Y2 - Temperature sensor using optical fiber - Google Patents

Description

[Detailed explanation of the idea] This invention relates to a temperature sensor using an optical fiber.

Research and development of various types of sensors using light is actively being carried out, and some have been put into practical use.

One of these various sensors is a temperature sensor.

In particular, such a temperature sensor is required to be small, lightweight, inexpensive, highly reliable, and not subject to electromagnetic induction.

Conventionally, as a temperature sensor of this type, an optical fiber temperature sensor that takes advantage of the non-inductive nature of optical fiber and changes the light intensity by shielding the light beam with a bimetal has been reported (e.g., (described in Proceedings of the National Conference of the Optical and Radio Waves Division of the Japan Society of Japan, 229) has bimetal movable parts, which makes it difficult to create a compact device, and the light beam is blocked to change the light intensity, which takes up a lot of space. However, the various components of the sensor cannot be integrated into an integrated structure, resulting in a lack of reliability.

An object of the present invention is to eliminate the above-mentioned drawbacks and provide an optical fiber temperature sensor that is small, lightweight, highly stable, easy to manufacture, inexpensive, and resistant to electromagnetic induction.

According to the present invention, the refractive index decreases according to the square of the distance from the central axis, and the end face is substantially perpendicular to the central axis,
A convergent light transmitter whose length is approximately (21"l-1)/4 pitch (n is a positive integer) in the meandering period of light, and a convergent light transmitter on one end surface of the convergent light transmitter. an optical fiber provided substantially parallel to the central axis of the optical fiber, a liquid crystal cell provided on the end face of the converging light transmitting body not facing the optical fiber, and a liquid crystal cell provided in the converging light transmitting body of the liquid crystal cell. A temperature sensor using an optical fiber is obtained, which is characterized in that it includes a reflector provided on the surface that does not face the temperature sensor.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a schematic diagram showing the first embodiment of this invention, in which 10 is a convergent optical transmission body with a length of approximately 1/4 pitch;
When the refractive index distribution is expressed as n=no(1-]722g2r2 (where r is the radius), the focusing parameter g is 0.3
mm-', the refractive index no on the central axis is 1.60, and the outer diameter is 2.
The length of 0 mm and 1/4 pitch is 5.2 mm.

20 is a liquid crystal cell in which a phase change type liquid crystal is confined in glass and a transparent electrode is attached, and has an outer diameter of 277Ell and a thickness of 2rIrIIL.

Reference numeral 30 denotes a reflector, and a dielectric multilayer film is provided as a total reflection film on the surface of the liquid crystal cell 20 that does not face the convergent light transmission body 10.

Further, reference numeral 40 denotes an optical fiber, which is provided on the end surface not facing the liquid crystal cell 20, approximately on the central axis of the convergent light transmission body 10.

In the above configuration, the light beam that propagates through the optical fiber 40 and enters the convergent light transmitter 10 expands the beam diameter and travels along the central axis of the convergent light transmitter 10 to become a parallel beam and becomes a parallel beam. enters the cell 20.

This light beam propagates within the liquid crystal cell, is totally reflected by the reflector 30, propagates within the liquid crystal cell 20 again, and then travels through the convergent light transmission body 10 while converging, and enters the optical fiber 40 again.

Here, the liquid crystal cell 20 has a change in transmittance with respect to temperature of about Q, 2dB10C (when 15V is applied), so the temperature can be measured by detecting the change in the amount of light beam emitted from the optical fiber 40 with a light receiving element. .

Since there is only one optical fiber, in addition to a light emitting element such as a light emitting diode and a light receiving element such as a photodiode, an optical branching and coupling circuit for separating sending and receiving signals is required, although not shown in the figure.

FIG. 2 is a schematic diagram showing a second embodiment of the present invention, and the difference from the first embodiment is that one optical fiber 4
The point is that two optical fibers 41 and 42 are used instead of 0.

In this embodiment, two optical fibers 41.
42, the optical branching and coupling circuit required in the first embodiment becomes unnecessary.

Note that the reflector 30 may be formed by providing a dielectric multilayer film or a total reflection film of metal such as aluminum or gold on a glass substrate and fixing it to the liquid crystal cell 20 with an adhesive.

FIG. 3 is a diagram showing an example of the mounting structure of the first embodiment of the present invention, and is shown so that a portion of the inside is visible.

45 is an optical fiber cord, 46 is a terminal member that protects the tip of the optical fiber 40 and has a polished end face, 11 is a cylindrical member in which the convergent light transmission body 10 is housed, and 21 is a reflector 30 provided on the end face. a cylindrical member containing a liquid crystal cell 20;
50 is a shrink tube, and 61 and 62 are lead wires from the electrodes of the liquid crystal cell 20.

Terminal member 46 and cylindrical member 11. Cylindrical members 11 and 21
They are each held together with adhesive and are made of plastic material.

The optical fiber temperature sensor according to this invention has been explained in detail using examples.The temperature sensor using optical fiber according to this invention can have an integrated structure of each component, is small, low loss, lightweight, and has high performance. It has features such as reliability, and is particularly well suited as a remote measurement sensor.

[Brief explanation of drawings]

1 and 2 are schematic diagrams showing the first and second embodiments of this invention, and FIG. 3 is a partially cutaway perspective view of the mounting structure of the first embodiment of this invention. It is a diagram. In the figure, 10... focusing optical transmission body, 11...
...Cylindrical member housing the focusing light transmission body, 20
...Liquid crystal cell, 21...Cylindrical member housing the liquid crystal cell, 30...Reflector, 40.41
．． 42... Optical fiber, 45... Optical fiber cord, 46... Terminal member, 50...
. . . Shrink tube, 61, 62 . . . Lead wires.

Claims (1)

[Scope of utility model registration request] The refractive index decreases approximately according to the square of the distance from the central axis, the end surface is approximately perpendicular to the central axis, and the length is approximately (2n-1)/4 pitch (n is a positive integer)
a convergent light transmitter, an optical fiber provided on one end surface of the convergent light transmitter substantially parallel to the central axis of the convergent light transmitter, and an optical fiber facing the optical fiber of the convergent light transmitter. An optical fiber characterized in that it is configured to include a liquid crystal cell provided on the end face of the liquid crystal cell and a reflector provided on the face of the liquid crystal cell on the side that does not face the focusing light transmission body. Temperature sensor used.