JPH0933586A - Photosensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the quantity of linearly polarized light entering a detecting section. SOLUTION: In this sensor, light emitted from a light source 11 and propagated through an optical fiber 12 is admitted into a detecting section 14 through a polarizer 13 and the light emitted from the detecting section 14 is propagated trough an optical fiber 15 to be admitted into a photodetector 16. A fiber 23 is used as a part of the optical fiber 12 in such a manner that a first polarization maintaining fiber 21 is connected to a second polarization maintaining fiber 22 with the length thereof at least doubling that thereof keeping the main axes thereof tilted by 45 deg. from each other. The fiber 23 makes the light from the light source 11 non-polarized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sensor such as an electric field sensor or a magnetic field sensor for measuring an electric field or a magnetic field from a change in a propagation state of light, and more particularly to a structure for transmitting light using an optical fiber for a detecting portion. Optical sensor.

[0002]

2. Description of the Related Art The structure of a conventional photosensor of this type is shown in FIG. The light emitted from the light source 11 is propagated by the optical fiber 12 and is incident on the polarizing plate 13, is linearly polarized and is incident on the detection unit 14. The detection unit 14 is composed of, for example, an electric field (voltage) sensor utilizing the Pockels effect, a magnetic field (current) sensor utilizing the Faraday effect, or the like.
It is appropriately selected according to the application.

The light that has passed through the detection section 14 has an optical fiber 15
And is incident on the light receiver 16 and the amount of incident light is measured. Then, from the change of the incident light amount, the detection unit 14
A change in the electric field or magnetic field acting on is detected.

[0004]

As described above, in this type of optical sensor, it is necessary to make the linearly polarized light incident on the detecting portion 14, and therefore the light that has propagated through the optical fiber 12 using the polarizing plate 13 is used. Is linearly polarized. By the way, a laser diode (LD) or a light emitting diode (LED) is generally used as the light source 11, and these L
The D and the LEDs have a polarization property, and the light propagating through the optical fiber is easily disturbed by a weak disturbance (temperature, pressure, vibration, etc.), that is, the polarization state fluctuates due to the disturbance. The light amount of the linearly polarized light after passing varies, resulting in poor accuracy and stability.

For this reason, conventionally, for example, a method of holding the optical fiber 12 so that it does not move or using an expensive polarization-maintaining fiber over the optical fiber 12 is used. However, none of them can completely eliminate the fluctuation of the polarization state, and the method of fixing and holding the optical fiber 12 is troublesome and the handling of the optical fiber 12 is restricted. The use was extremely expensive, and there was a problem in terms of cost.

The object of the present invention is to eliminate these drawbacks of the prior art and to stabilize the quantity of linearly polarized light incident on the detecting section with a simple and inexpensive structure, thereby performing accurate and stable detection. It is to provide an optical sensor capable of

[0007]

According to the present invention, the light emitted from the light source and propagated by the optical fiber is incident on the detection section through the polarizing plate, and the light emitted from the detection section is transmitted by the optical fiber. In an optical sensor configured to propagate and enter a light receiver, a part of an optical fiber between a light source and a polarizing plate has a first polarization-maintaining fiber and a length of the first polarization-maintaining fiber. A fiber formed by connecting at least twice the second polarization-maintaining fiber with their main axes inclined at 45 ° to each other is used with the first polarization-maintaining fiber as the light source side.

[0008]

FIG. 1 shows an embodiment of the present invention.
In this example, a fiber 23 formed by connecting two polarization-maintaining fibers 21 and 22 is connected to a light source 11, and a normal optical fiber 12 is connected to this fiber 23, that is, light between the light source 11 and a polarizing plate 13. A part of the fiber 12 is replaced with the fiber 23.

As shown in FIG. 1B, the fiber 23 is a first polarization-maintaining fiber (hereinafter referred to as the first fiber).
21 and a second polarization-maintaining fiber (hereinafter referred to as a second fiber) 22 are arranged such that their axes (core portions) are coincident with each other, and their principal axes x are inclined at 45 ° with respect to each other. The length L ₂ of the two fibers 22 is equal to the first fiber 21.
Is at least twice the length L ₁ . The length L ₁ of the first fiber 21 is set so that the phase difference between the principal axis x and the minor axis y of the first fiber 21 is equal to or longer than the coherent length of the incident light wave.

According to this fiber 23, when arbitrary linearly polarized light is incident on its end face 23a, it is demultiplexed into x-polarized light and y-polarized light which do not interfere with each other due to the difference in the propagation constants in the first fiber 21, and further the second polarized light. In the fiber 22, they are demultiplexed into the x-polarized wave and the y-polarized wave, respectively, and finally the end face 23a
The linearly polarized light incident on is split into x-polarized light and y-polarized light which have the same amplitude and do not interfere with each other, and become a non-polarized state and are emitted from the end face 23b.

Therefore, by using this fiber 23 as a part of the optical fiber 12 between the light source 11 and the polarizing plate 13 so that the first fiber 21 is on the light source 11 side, the light emitted from the light source 11 is polarized. Even if it has a state, it can be made into a non-polarized state, so that the variation in the amount of linearly polarized light after passing through the polarizing plate 13 due to the influence of disturbance can be eliminated.

FIG. 2A shows an example in which polarizing plates 13 are arranged before and after the detection section 14, and FIG. 2B shows the details. As shown in FIG. 2B, rod lenses 24 are attached to the output end of the optical fiber 12 and the input end of the optical fiber 15, respectively. This figure 2
In the above configuration, the detecting unit 14 is a liquid crystal cell in which the liquid crystal array changes depending on the strength of the electric field to change the light transmittance, and the electric field strength acting on the detecting unit 14 is kept constant to give a disturbance to the optical fiber 12. The amount of light incident on the light receiver 16 at that time was monitored. In addition, the first fiber 21 and the second fiber of the fiber 23
Each length of the fiber 22 was 1 m and 2 m. As a result of monitoring the amount of incident light, it was confirmed that the amount of light did not fluctuate even when a disturbance was given to the optical fiber 12, and an extremely stable amount of light was obtained.

The detection unit 14 is, for example, a BSO crystal (Bi ₁₂ S).
For example, an electric field sensor using the Pockels effect may be used using iO ₂₀ ) or the like, and a magnetic field sensor using the Faraday effect using a magnetic substance crystal such as YIG may be used. FIG. 3A shows another embodiment of the present invention, in which a plurality of detecting portions 31 with polarizing plates are connected in parallel between the optical fibers 12 and 15, and an optical pulse transmitter 32 is used as a light source.
In an optical sensor using the optical pulse receiver 33 as a light receiver, the optical fiber 12 is connected to the optical pulse transmitter 32 via the fiber 23 described above.

Further, FIG. 3B shows an optical sensor in which a plurality of detecting portions 31 with polarizing plates are attached with reflecting plates 34 and these are connected to an optical fiber 12 connected to an optical pulse transmitter / receiver 35. The optical fiber 12 is connected to the transceiver 35 via the fiber 23. In each of the above examples, the fiber 23 is connected to the light source, but the fiber 23 may be partially used at an arbitrary position between the light source and the polarizing plate.

[0015]

As described above, according to the present invention, the polarization state of the light emitted from the light source 11 is replaced by a part of the optical fiber 12 between the light source 11 and the polarizing plate 13, and the fiber 23 is provided. Since it becomes a non-polarized state by propagating, the problem that the polarization state changes due to disturbance is solved, and thus the amount of linearly polarized light that passes through the polarizing plate 13 and enters the detection unit 14 does not change due to disturbance. Since it becomes stable, accurate and stable detection can be performed.

Since only a part of the optical fiber 12 between the light source 11 and the polarizing plate 13 uses the fiber 23 formed by connecting the two polarization-maintaining fibers 21 and 22, the influence of disturbance is exerted. It is possible to easily and inexpensively configure an optical sensor that does not receive the light.

[Brief description of drawings]

FIG. 1A is a diagram for explaining a first embodiment of the present invention, and B is an exploded perspective view for explaining a connection state of two polarization-maintaining fibers.

2A is a diagram for explaining a second embodiment of the present invention, and B is a partial detailed diagram of A. FIG.

FIG. 3A is a diagram for explaining a third embodiment of the present invention, and B is a diagram for explaining a fourth embodiment of the present invention.

FIG. 4 is a diagram for explaining a conventional optical sensor.

[Explanation of symbols]

 11 Light Source 12 Optical Fiber 13 Polarizing Plate 14 Detector 15 Optical Fiber 16 Light Receiver 21 Polarization Preserving Fiber 22 Polarization Preserving Fiber 23 Fiber

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location G02B 6/00 G01R 15/07 C G02B 6/00 B

Claims (1)

[Claims] 1. A structure in which light emitted from a light source and propagated by an optical fiber is incident on a detector through a polarizing plate, and light emitted from the detector is propagated by an optical fiber and incident on a light receiver. In the above optical sensor, a part of the optical fiber between the light source and the polarizing plate has a first polarization-maintaining fiber and a second polarization-maintaining fiber whose length is at least twice as long as that of the first polarization-maintaining fiber. An optical sensor characterized in that a fiber formed by connecting a polarization maintaining fiber to each other with their principal axes inclined at 45 ° to each other is used as the light source side of the first polarization maintaining fiber.