JPS61212773A - Photosensor - Google Patents

Abstract

PURPOSE:To achieve a higher sensitivity of a photo sensor, by a method wherein opposed two planes of a medium are tapered at a specified angle and a polarized light from a polarizing means is made incident on the medium to be reflected on the two planes facing each other several times and the polarization component of a specified direction is taken out with a photo detection element on one end side larger in the interval between the two planes of the medium. CONSTITUTION:Opposed reflecting surfaces 7 of a medium 1 comprising an electrooptic material or a magnetooptic material are tapered at a certain angle (2alpha). A light L1 made incident into a horizontal plane 9 at an incident angle theta is converted into linearly polarized or circularly polarized light by a polarization means 8 and reflected on a reflecting surface 7 inclined by an angle alpha of from the horizontal plance 9. Then, as the reflection is repeated on the reflecting surface 7, the incident angle of the light approaches zero gradually and finally reaches zero, where the light returns to the incidence side again and turns to an emission light l2 to obtain a propagation optical path longer in substance in the medium 1. Since the angle of rotation of the polarization surface to the emission of the light from the incidence thereof into the medium 1 is proportional to th propagation optical path length therein 1, the longer the propagation optical path length, the higher the sensitivity of a photosensor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to optical sensors that detect electric or magnetic fields.

BACKGROUND OF THE INVENTION In recent years, with the development of optical fiber technology, in the field of measurement, desired measurement items are measured by detecting changes in the physical properties of various transparent and reflective media using light. Optical sensors are increasingly being introduced. In particular, optical fibers are electrically insulating and non-inductive, so if you use a sensor system in combination with an optical sensor with similar properties to detect electric and magnetic fields and measure voltage and current, High voltage technicians can perform measurements without running the risk of electric shock and the like associated with measurements using metal lines. Therefore, in the power field, there is a great demand for the practical application of highly sensitive optical sensors for detecting electric and magnetic fields.

A configuration diagram of a conventional optical sensor for detecting an electric field is shown in FIG. The incident light is converted into linearly polarized light through a polarizer 2, and into circularly polarized light through a wavelength plate 3, and is incident on a medium 1 having an electro-optic constant at an incident angle θ.

A total reflection film 6 is added to two opposing parallel planes 7 of the medium 1, and after this light undergoes multiple reflections between the two planes and six planes 7, it passes through a polarization compensator 5 and an analyzer 4 and becomes an output light. It becomes L2.

By the way, if we assume that an electric field E is applied to the medium 1 at this time, the refractive index ellipsoid of the medium 1 having an electro-optic constant causes deformation, and the medium 1 exhibits birefringence according to the magnitude of the electric field E. Therefore, the incident light converted into circularly polarized light by the polarizer 2 and wavelength plate 3 becomes elliptically polarized light by passing through the medium 1. Therefore, the energy of the emitted light L2 that has passed through the polarization compensator 5 and the analyzer 4 corresponds to the magnitude of the electric field E, and by measuring this energy, the magnitude of the electric field E can be determined.

On the other hand, the optical sensor for detecting a magnetic field has a structure in which the two-wavelength plate 3 of the optical sensor for detecting an electric field shown in FIG. 5 is removed, and a medium having a magneto-optic constant is provided in place of the medium 1.

Then, the incident light L converted into linearly polarized light by the polarizer 2
1 passes through the medium.

At this time, if the magnetic field H is present, a Faraday effect occurs, and the polarization plane of the linearly polarized light rotates according to the magnitude of the magnetic field H, and the linearly polarized light is incident on the polarization compensator 5 and the analyzer 4. Therefore, if the analyzer 4 is installed in advance so as to be orthogonal to the plane of polarization when the magnitude of the magnetic field H is 0 and the plane of polarization does not rotate, the energy of the emitted light L2 will depend on the magnitude of the magnetic field H. It becomes something.

That is, the magnitude of the magnetic field H can be determined by detecting the energy of the emitted light L2.

Problems to be Solved by the Invention Since the rotation angle of the plane of polarization from the time it enters the medium 1 to the time it exits is proportional to the length of the optical propagation path in the medium 1, the greater the length of the optical propagation path, the greater the sensitivity of the optical sensor. It gets expensive. For example, compared to an optical sensor in which the incident light passes through the medium 1 only once,
An optical sensor that reflects once on a reflective surface and passes through medium 1 twice has twice the propagation path length, that is, has twice the sensitivity, and similarly, when reflected n times, it has n+1 times the sensitivity.

In a multiple reflection type optical sensor as shown in Fig. 5, the propagation optical path length differs depending on the incident angle θ, but in reality the incident angle θ is a small value, so the sensitivity m is determined by the number of reflections n. I can say it. From Fig. 5, the number of reflections n is β n= -1 (1) Wl tanθ where l: effective length of medium 1 W: thickness of medium 1 θ: angle of incidence, and sensitivity m is as follows. It is expressed by the formula.

m= (n+ 1)XEXP = C] θ=
When the angle is 10°, the sensitivity m=11·E−P. Here, since the electro-optical constant P is a value specific to the crystal of medium 1, the sensitivity m is proportional to the length l of the crystal constituting medium 1, and inversely proportional to the thickness W of the crystal and the tangent tanθ of the incident angle θ. do. Therefore, in order to increase the sensitivity m, the crystal length l may be increased, the crystal thickness W may be reduced, or the tangent tan θ may be reduced.

Incidentally, when the tangent tan θ is below a certain value, that is, when the incident angle θ is below a certain value, the incident point P.

Since the distance between the light beam and the first reflection point P1 on the reflection surface 7 on the incident side becomes less than the diameter of the luminous flux, efficient energy injection is no longer performed, so the tangent tan θ must be set to a certain value or more. Therefore, in order to increase the sensitivity m,
Crystal length! must be set as large as possible compared to the thickness W.

Note that the same can be said of the optical sensor for detecting a magnetic field.

As described above, conventionally, when attempting to realize a highly sensitive multiple reflection type optical sensor, the sensor becomes large in size.

An object of the present invention is to provide a compact and highly sensitive optical sensor.

Means for Solving the Problems As shown in FIG. 1, the optical sensor of the present invention has a tapered structure in which the opposing reflecting surfaces 7 of the medium 1 are not parallel but are arranged at a certain angle (2α). As the light L1 enters at an incident angle θ and is repeatedly reflected on the reflecting surface 7, the incident angle gradually approaches 0, and finally reaches 0 and returns to the incident side again to become the output light L2, which causes light to enter the medium 1. In this case, a substantially long optical path length is obtained.

In a preferred embodiment of the present invention, as shown in FIG. 2, a substance 11 having a higher refractive index than the medium 1 is provided between the polarizing means 8 for generating linearly polarized light or circularly polarized light, the analyzer 4, and the medium 1. It has been inserted.

First, the operating principle of the optical sensor according to the present invention will be explained. FIG. 3 is an enlarged view of the dotted line section A in FIG. In this figure, light incident on a horizontal surface 9 at an incident angle θ is converted into linearly polarized light or circularly polarized light by a polarizing means 8, and then reflected by an inclined reflecting surface 7 forming an angle α with the horizontal surface 9. Ru. At that time, the reflection angle of the reflected light L3 with respect to the horizontal plane 9 is θ
-2α. Next, the reflected light L3 similarly enters the opposing reflecting surface 7 that forms an angle of α with the horizontal surface 9 at an incident angle θ−2α with respect to the horizontal surface 9, and this time, the reflected light L3 enters at an incident angle θ−2α with respect to the horizontal surface 9.
It is reflected by 4α.

When the light is reflected n times by the opposing reflecting surfaces 7 in this manner, the angle of incidence with respect to the horizontal surface 9 becomes θ-2nα. Here, if the angles θ and α are set to appropriate values in advance, the incident angle will be θ−2nα=0 at a certain number of reflections n.
...(3), and the incident light is as shown in Figure 1,
After passing through an optical path that is vertically symmetrical to the optical path that has been traced so far and being reflected n times at the reflecting surface 7, the polarization compensator 5 and the analyzer 4
It becomes the emitted light L2. That is, from equation (3), n
= θ/2α, so the number of round-trip reflections N is: N=2n=2 (θ/2 cx ) ・・・・・・(
4).

The sensitivity of this optical sensor is determined by the number of reflections N,
Taking an optical sensor for detecting an electric field as an example, the formula (2) is as follows. In this case, the distance l from the light incidence point of the medium 1 to the turning point where the incident angle becomes 0 is expressed by the following equation, so the medium 1 must have a length equal to or greater than this distance 1.

2 ta mouth α
...(6) However, W is the maximum thickness of the medium 1.

As can be seen from equation (5), the sensitivity m is determined by the incident angle θ and the angle α of the reflecting surface 7 with respect to the horizontal plane 9. For example, if the incident angle θ=10°, when α=1°, 1. : m=11EXP, m=21XEX when α=0.5
When P, a= 0°1°, m= l0IXEXP.

According to equation (3), theoretically, the smaller the angle α, the higher the sensitivity m becomes. However, as the angle α becomes smaller, the propagation optical path becomes longer and the insertion loss increases. When the increase in sensitivity m becomes equal to the increase in insertion loss, the effect of increasing sensitivity becomes zero from a system perspective. That is, this time becomes the lower limit value of the angle α. The lower limit value of the angle α will be explained below.

The general optical path length of the optical sensor of the present invention is expressed as follows.

W: Thickness of the medium N: Number of reflections θ: Incident angle By the way, since the total reflection film 6 is generally composed of a multilayer film, it is well known that the reflection characteristics will deteriorate unless the incident angle θ is 15° or less. be. Therefore, the number of reflections N is set to 100.
If the value is set to a value larger than 100, the equation (7) can be approximated as follows.

L=NW (8) Also, in order for the light beams to efficiently propagate inside the medium 1 without overlapping each other at each reflection point on the reflection surface 7, the thickness of the medium is set to W1. The interval W between each reflection point, where the angle of human incidence is θ and the diameter of the luminous flux is a
It is necessary that tan θ is twice or more the diameter of the luminous flux. That is, W tanθ≧2a ”(
9).

Considering that the core diameter of the excitation fiber is 50 μm, the diameter a of the light beam propagating in the medium 1 cannot be narrowed down to less than 50 μm, and the maximum value of the incident angle θ is 15° (9)
From the equation, it can be seen that the following relational expression holds true.

W2O, 373 (mm) ``'' 1 mouth Substituting this α1 formula into formula (8), then ≧0.373・N (mm) ・・・(11
).

FIG. 4 shows the insertion loss when the diameter a of the medium-propagating light beam is 100 μm. Using equation (11), the propagation optical path length in Fig. 4 is converted into the number of reflections N, and as mentioned above, the sensitivity of the multiple reflection type optical sensor with the number of reflections N is N+1 times as compared to the case where the number of reflections is 0. Therefore, by expressing the multiple N+1 of this sensitivity in decibels, the conduction optical path length is LLlmm.
When the sensitivity is 24.7 dB, that is, 300 times higher, the insertion loss is also 24.7 dB, and it can be seen that the sensitivity of 300 times is the limit of high sensitivity.

At this time, from equation (4), 299=θ/α (12),
Further, when the maximum value of the incident angle θ, 15°, is substituted into this equation (12), the lower limit value of the angle α becomes 0.05°.

That is, the angle 2α formed by the reflective surface 7 needs to be 0.1° or more.

Also, when actually manufacturing an optical sensor like the one shown in Figure 1,
Since the incident angle is small, in the enlarged view of FIG. 3, the distance S between the emitted light L2 from the medium 1 having an electro-optic constant or magneto-optic constant and the reflected light L3 by the reflecting surface 7 is small;
It is not easy to separate these lights L2 and L3. For example, the thickness W is 5 mm.

When the incident angle θ is 10°, the distance S between the emitted light L2 and the reflected light L3 is 1.76 mm, and assuming that the diameter of the light beam is 1 mm, there is no margin for separation of 0.76 aun. becomes difficult.

Therefore, as shown in FIG. 2, a medium 11 having a higher refractive index than the medium 1 is inserted between the medium 1 having an electro-optic constant or a magneto-optic constant and the polarizing means 8 and the polarization compensating plate 5. Then, since the incident light L1 is refracted when it enters the medium 1 from the medium 11, and the outgoing light L2 is refracted when it enters the medium 11 from the medium 1, the incident angle θ of the incident light with respect to the horizontal plane 9 and the outgoing light L2 Both of the take-out angles θ can be set large. Therefore, the output light L
2 from the reflected light L3 on the reflecting surface 7 or from the incident light L1.

Note that the refractive index of the medium 11 needs to be kept low enough to prevent total reflection when light is incident on the medium 1. Further, it is desirable that the interface between the medium 1 and the medium 11 be coated with an antireflection film to suppress reflection of light.

Note that the above-mentioned effects have been described in the case where the mutually opposing reflecting surfaces 7 of the medium 1 are inclined symmetrically with respect to the horizontal plane 9. However, in the present invention, only one of the pair of opposing reflecting surfaces 7 may be inclined with respect to the horizontal surface 9, and the other reflecting surface may be parallel to the horizontal surface 9. In that case, if the angle formed by the pair of reflecting surfaces is 2α, the only difference is that the angle of the light with respect to the horizontal plane 9 decreases by 4α for each reflection on the inclined reflecting surface, and the above relationship is the same. This is true, and similar effects can be obtained.

Example Examples of the present invention will be described below.

Example 1 In the first example, in FIG. 1, the medium 1 is 8! having a thickness of 0.5 mm and a length of 4.3 mm. A +zS10□o crystal was used, and the surfaces were polished into a tapered shape so that the angle 2α between the opposing surfaces was 0.1°. Next, Ti is deposited on these surfaces.
A total reflection film 6 made of a multilayer film of O2 and Sin is formed.

Further, parts of the opposing surfaces of the medium 1 are polished so that they form an angle of 10° with respect to the horizontal plane 9, and an X wavelength plate and a polarizer are provided as polarizing means 8 on one side, and a polarization compensating plate 5 and a polarizer on the other side. An analyzer 4 was provided to constitute an optical sensor for detecting an electric field.

When the electric field was measured with light incident at an incident angle of 10', a sensitivity more than 10 times that of the conventional multiple reflection type optical sensor shown in FIG. 5 was obtained.

Example 2 In the second example, in FIG. 2, the same B11°5iO2o crystal as the first example was used as the medium 1, and the angle 2α formed by the tapered surface was 0.1°. A total reflection film 6 made of a multilayer film of Ti1t and SiO□ was formed on these surfaces. Next, GaP is used as the medium 11 and installed so as to be in contact with one thick end surface of the medium 1, and further an X wavelength plate and a polarizer are provided as the polarizing means 8 in the same manner as in the first embodiment. A polarization compensation plate 5 and an analyzer 4 were also provided to form an optical sensor for detecting an electric field.

The refractive index of medium 1 (Bi, 2SiO□.) and (GaP) is 2.45.3.31, respectively, and the horizontal plane 9
On the other hand, when the angle of incidence on the medium 11 was set to 47°, the angle of incidence on the medium 1 was 9°, and the same sensitivity as in the first example was obtained in the measurement of the electric field.

In Example 1.2, the medium 1 having an electro-optic constant is Bi+2S! 02o was used, but ZnS.

Zn5eSLiNbOa, Bt4(GeO4)+, Bj
4(SLOn)i, Bi+zGeOzo can also be used.

Moreover, when configuring an optical sensor for detecting a magnetic field, FR-5 or ZnS having a magneto-optical constant is used as the medium 1.

It is sufficient to use Bi+2GeOzo or the like, and use only a polarizer as the polarizing means 8.

Furthermore, in the above embodiment 1.2, the total reflection film 6 is TlO.
Although a multilayer film made of 2.Sin was used, a film made of other dielectric materials may be used. However, gold, A1, and the like, which are generally used as reflective films, have different reflectances for P-polarized light and S-polarized light, so it is not preferable to use them in the optical sensor of the present invention.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention as described above, it is possible to provide an optical sensor that is small but has very high sensitivity. Therefore, by using the optical sensor of the present invention, it is possible to safely and accurately measure voltage and current even under high voltage, so the present invention is useful in the electric power field and the like.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical sensor according to an embodiment of the present invention,
Fig. 2 is a block diagram of another embodiment, Fig. 3 is a partially enlarged view of the embodiment of Fig. 1, Fig. 4 is a graph showing insertion loss versus propagation optical path length, and Fig. 5 is a diagram of a conventional optical sensor. FIG. (Main reference numbers) L,...Incoming light, L2...Outgoing light, 1...Medium having an electro-optic constant or magneto-optic constant, 2...Polarizer, 3...A wavelength plate, 4...Detection Photon, 5. Polarization compensation plate, 6. Total reflection film, 7. Reflection surface, 8. Polarizing means, 9. Horizontal surface, 11. Medium

Claims (8)

[Claims] (1) A medium made of an electro-optic material or a magneto-optic material, a polarizing means for inputting polarized light into the medium, and an analyzer for receiving light emitted from the medium, and the polarized light from the polarizing means is transmitted to the medium. In the optical sensor, the light enters the analyzer and after being reflected multiple times on two opposing planes of the medium, the polarized light components in a predetermined direction are extracted, the two planes of the medium forming a predetermined angle. The polarizing means and the analyzer are formed in a tapered shape.
An optical sensor characterized in that the optical sensor is located on one end side of the medium where the distance between the planes is wide. (2) The optical sensor according to claim 1, wherein the predetermined angle is 0.1° or more. (3) The optical sensor according to claim 1 or 2, wherein the polarizing means emits circularly polarized light, and the medium is made of an electro-optic material. (4) The optical sensor according to claim 1 or 2, wherein the polarizing means emits linearly polarized light, and the medium is made of a magneto-optical material. (5) The first layer is made of an electro-optic material or a magneto-optic material.
a medium, a polarizing means for inputting polarized light into the first medium, and an analyzer for receiving light emitted from the first medium, the polarized light from the polarizing means is input to the first medium. , an optical sensor in which a polarized light component in a predetermined direction is extracted by entering the analyzer after being reflected multiple times on two opposing planes of the first medium, wherein the two planes of the first medium are in a predetermined direction. The polarizing means and the analyzer are formed in a tapered shape at an angle of
located on one end side of the first medium where the distance between the two planes is wide, and inserted between the polarizing means and the analyzer and the first medium; An optical sensor comprising a second medium having a refractive index greater than the refractive index of the second medium. (6) The optical sensor according to claim 5, wherein the predetermined angle is 0.1° or more. (7) The optical sensor according to claim 5 or 6, wherein the polarizing means emits circularly polarized light, and the first medium is made of an electro-optic material. (8) The optical sensor according to claim 5 or 6, wherein the polarizing means emits linearly polarized light, and the first medium is made of a magneto-optical material.