JP3215861B2 - Magneto-optical element and current measuring device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical device made of a medium having a Faraday effect and a current measuring device using the magneto-optical device.

[0002]

2. Description of the Related Art Conventionally, four glass rods having a Faraday effect are formed in a rectangular frame shape to form an optical closed circuit, and a current is passed through the frame surface of the optical closed circuit.
Polarized light is incident from one corner of the frame, reflected at three angles at right angles, and then polarized light is emitted from near the point of incidence. Photoammeters for measuring are known. This photoammeter is being put to practical use as an alternative to electrical CT in the power field.

In such a conventional photoammeter, since the total reflection of the prism is used in the three corner reflection portions of the optical closed circuit, it is necessary to correct a change in polarization generated at the time of total reflection. is there. For this purpose, two orthogonally arranged total reflection surfaces are provided to correct the polarization change.

[0004]

For this reason, the conventional photoammeter has a number of problems, such as a complicated structure, a large amount of materials, and a low productivity. Further, since the polarized light is not linearly polarized between two orthogonally arranged total reflection surfaces, there is a problem that a measurement error occurs if a magnetic field parallel to the optical path exists in this portion.

[0005]

A magneto-optical device according to the present invention comprises a medium made of a material having a magneto-optical effect. Light incident inside the medium is reflected by a plurality of reflecting surfaces on the surface and emitted from near the incident point. The reflective surface is formed of a dielectric multilayer film, and the refractive index and the incident angle of the medium are adjusted so that the incident angle of light on the reflective surface is equal to or greater than the Brewster angle and equal to or less than the critical angle. It is set.

In addition, the current measuring device according to the present invention uses the magneto-optical element to form a current path in a space surrounded by an optical path of light reflected in the medium, and according to the amount of current flowing through the path. Thus, the amount of polarization of light is changed, and the amount of current is measured from the amount of polarization.

[0007]

In each of the reflecting surfaces, the incident angle of light is equal to or greater than the Brewster angle and equal to or less than the critical angle. Therefore, the phase of the reflected light is the same with respect to straight lines that are parallel and perpendicular to the incident surface. For this reason, if the thickness of each multilayer film on the reflecting surface is reduced to 1/4 of the oblique ray, all the partially reflected waves generated on each reflecting surface can be overlapped with the same phase. Therefore, by sufficiently increasing the number of films, the amplitude reflection coefficient R _s = R _p = 1 for both the parallel polarization (P) and the vertical polarization (S).
Can be realized. That is, there is a possibility of realizing a completely isotropic optical path.

When a current is passed through the optical closed circuit in the medium, the magneto-optical effect caused by the magnetic field generated at each point in the medium is preserved along the optical path. Since there is no change, the current amount can be accurately measured from the measurement of the polarization rotation angle of the emitted light.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magneto-optical element and a current measuring device according to the present invention will be described in detail. FIG. 1 is a front view of one embodiment of the magneto-optical element of the present invention. 1 is a hexagonal medium made of a material having a Faraday effect which is a magneto-optical effect,
A hole 2 through which the electric wire passes when measuring the current is formed at the center. Reference numeral 3 denotes an entrance / exit surface on which light rays enter or exit, and reference numerals 4a, 4b, and 4c denote reflection surfaces.

When the incident light 5a is incident on the entrance / exit surface 3 at a predetermined angle, the light beam enters the inside of the medium 1 and the reflecting surfaces 4a,
The light is sequentially reflected by 4b and 4c, and is emitted as emission light 5b from the same point as the incident point on the entrance / exit surface 3 or a point close to the incident point. An anti-reflection film can be formed on the entrance / exit surface 3 in order to make incident light efficiently enter the medium.

FIG. 2 is an enlarged sectional view of the reflecting surfaces 4a, 4b, 4c. On the surface (outer surface) of the reflection surface of the medium 1, a multilayer film is formed. 4a ₁ first thickness _{D 1} at a refractive index _{N 1} is the dielectric film, 4a ₂ second thickness _{D 2} at the refractive index _{N 2}
Is a dielectric film. On the dielectric films 4a ₁ and 4a ₂ , the same third and fourth dielectric films 4a ₃ and 4
a ₄ is formed, the multilayer dielectric film is formed of the two dielectric films as a unit. The medium 1 has a refractive index N
_{Has zero} .

Light transmitted through the medium 1 is converted into a dielectric film 4a.
When an incident angle A ₀ to _1, a portion is reflected, a portion is incident on the dielectric film 4a _1. The light incident on the dielectric film 4a ₁ is incident at an incident angle A ₁ into the dielectric film 4a _2, a portion thereof is reflected at the boundary surface, a portion is incident on the dielectric film 4a _2. The dielectric film 4a is the light incident on the _second incident angle _{A 2} in the dielectric film 4a ₃
In incident portion is reflected at the boundary surface, a portion is incident on the dielectric film 4a _3. As described above, the light beam incident on the multilayer film from the medium 1 returns to the medium 1 by repeating reflection as indicated by the dotted optical path. Similar reflection is performed on each reflection surface.

In this reflection, the following equation is established. N ₀ sinA ₀ = N ₁ sinA ₁ = N ₂ sinA ₂

FIG. 3 is a diagram used to design a magneto-optical element having desired characteristics. The horizontal axis right from 0, si angle of incidence _{A 0} for the first dielectric film 4a ₁ from the medium 1
n value, the vertical axis represents sin value of the angle of incidence _{A 1} of the first dielectric film 4a ₁ to the second dielectric film 4a _2, the horizontal axis of the left from 0, the second dielectric film 4a ₂ 3 dielectric film 4a ₃
Is a sin value of the angle of incidence _{A 2} against.

[0015] The well-known law of refraction, the relationship refraction between the medium 1 and the first dielectric film 4a ₁ is on a straight line 0Q, first dielectric film 4a ₁ second dielectric film relationship refraction and 4a ₂ are on a straight line 0S. A semicircle C with a radius of 1 is
This is the condition of the incident angle corresponding to the Brewster angle. Semicircle C
The rectangle circumscribing is the condition corresponding to the criticality of total reflection at each boundary reflection surface.

In order to satisfy the conditions of the present invention, the angle of incidence must be outside the semicircle C and inside the rectangle, that is, on the line segments PQ and RS. Therefore,
The incident angle satisfying the condition is, for example, A ₀ = B in FIG.
₀ (sinA ₀ = sinB ₀ ), A ₁ = B ₁ (sin
A ₁ = sinB ₁ ), A ₂ = B ₂ (sinA ₂ = s
inB ₂ ). The intersection of this condition with the line segment PQ is X,
Assuming that the intersection with the line segment RS is Y, the line segment XY is parallel to the horizontal axis.

FIG. 4 shows a specific embodiment of the magneto-optical element according to the present invention.
Using glass (refractive index N ₀ = 1.84), a light beam (wavelength λ = 633 nm) is incident and reflected at an angle as shown in the figure. Then, as the dielectric film 4a ₁ of the first (second 3), S
iO ₂ (N ₁ = 1.45), second (fourth) dielectric film 4
using _TiO 2 _(N 2 = 2.25) as a _2.

Under these conditions, each incident angle is B ₀ = 5
When 0 ° is set, B ₁ = 76.4 ° and B ₂ = 38.8 °
Becomes This B0 = 50 ° corresponds to the difference between the medium 1 and the first dielectric film 4.
In the boundary reflection surface of a _1, Brewster angle = 38.2 °, in the range of the critical angle 52.0 °. Further, in the first dielectric film 4a ₁ and the boundary reflection surface of the second dielectric film 4a _{2, B} 1 =
76.4 ° is a Brewster angle of 57.1 ° and a critical angle = 9.
It is in the range of 0 °. This result satisfies the required conditions shown in FIG.

Here, in the thickness of each dielectric film, D ₁ = λ / (4N ₁ cosB ₁ ) = 463.27n
m, D ₂ = λ / (4N ₂ cosB ₂ ) = 90.19 nm
Then, since each of the dielectric films has a quarter wavelength, partially reflected light on each boundary reflection surface causes constructive interference. For example, when 8 pairs of units of the dielectric film, the amplitude reflectance factor _R s ₌ 1.0000, reflections held R p = 0.99997. Therefore, the polarization can be achieved.

FIG. 5 is a block diagram of a current measuring device using the magneto-optical element of the present invention. An electric wire 16 for passing a current to be measured is inserted into a hole 12 at the center of the magneto-optical element 10. I have. The laser beam 15 is transmitted through the polarizer 17 and enters the magneto-optical element 10, internally reflected by the respective reflection surfaces in the medium as described above, makes one round, and exits from the same point as the incident point. The emitted laser light has its polarization angle rotated according to the amount of current flowing through the electric wire 16, and this emitted light passes through the analyzer 18 and is detected by the detector 19 composed of a photoelectric converter. The amount of detected light is proportional to the amount of current flowing through the wire 16. If the azimuth of the transmission axis of the analyzer 18 is set to 45 ° with respect to the polarization azimuth received at the time of transmission through the end face at the time of emission, the measurement sensitivity is maximized.

[0021]

According to the present invention, since a closed circuit of light can be formed in a medium in which a reflection film for retaining polarized light is formed, it is possible to make the entire optical path optically isotropic. When such a magneto-optical element is used for current measurement, a current flowing in any direction can be measured very accurately.

[Brief description of the drawings]

FIG. 1 is a front view of one embodiment of a magneto-optical element according to the present invention.

FIG. 2 is an enlarged sectional view of a reflection surface of the magneto-optical element of FIG.

FIG. 3 is a diagram used to design a magneto-optical element having desired characteristics.

FIG. 4 is a front view showing a specific example of the magneto-optical element of FIG. 1;

FIG. 5 is a configuration diagram of a current measuring device using the magneto-optical element of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 medium having magneto-optical effect 2 hole 3 entrance / exit surface 4a, 4b, 4c reflection surface 5a incident light 5b exit light 10 magneto-optical element 12 hole 15 laser light 16 electric wire 17 polarizer 18 analyzer 19 detector 19

Claims (2)

(57) [Claims] 1. A medium made of a material having a magneto-optical effect, wherein light incident on the medium is reflected by a plurality of reflection surfaces on the surface and emitted from near an incident point, and the reflection surface is made of a dielectric material. And a refractive index of the medium and the dielectric and the incident angle are set so that the incident angle of light on the reflecting surface is not less than the Brewster angle and not more than the critical angle. 2. Use of the magneto-optical element according to claim 1,
A current path is formed in a space surrounded by an optical path of light reflected in the medium, the amount of polarization of light is changed according to the amount of current flowing through the path, and the amount of current is measured from the amount of polarization. Current measuring device.