JPH05196653A - Magneto-optical element and current measurement device using this - Google Patents

Abstract

PURPOSE:To provide a magneto-optical element for measuring current accurately through a Faraday effect by providing a reflecting surface of simple structure that can retain polarization. CONSTITUTION:A hole 2, through which current runs, is formed in the center of a medium 1 having a Faraday effect, and when a light beam is incident on an incident surface 3, the light incident in the medium is reflected by reflecting surfaces 4a, 4b, 4c, and is outputted from the same point. When current runs through the hole, transmitted light in the medium is polarized and rotated according to the level of the current. A multilayer film of a dielectric is formed on each reflecting surface, and the incident angles for the medium and for the dielectric are set so that the incident angle to the reflecting surface is not less than an angle of polarization and not more than a critical angle.

Description

Detailed Description of the Invention

[0001]

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

[0002]

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

Since such a conventional photoammeter utilizes the total reflection of the prism at the three corner reflection portions of the optical closed circuit, it is necessary to correct the change in the polarization generated during the total reflection. is there. Therefore, two total reflection surfaces arranged orthogonally are provided to correct the change in polarization.

[0004]

For this reason, the conventional photoammeter has many problems such as a complicated structure, a large amount of materials, and poor productivity. Further, since the polarized light is not linearly polarized light 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 element according to the present invention is made of a medium made of a material having a magneto-optical effect, and light incident on the inside of the medium is reflected by a plurality of reflecting surfaces on the surface and emitted from near the incident point. This 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 not less than Brewster's angle and not more than the critical angle. It has been set.

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

[0007]

In each reflecting surface, since the incident angle of light is greater than the Brewster's angle and less than the critical angle, the phase of the reflected light is the same with respect to the straight lines deviated in parallel and perpendicular to the incident surface. For this reason, if each film thickness of the multilayer film on the reflecting surface is set to 1/4 with respect to 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 parallel polarized light (P) and vertical polarized light (S).
Will 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 due to the magnetic field generated at each point in the medium is preserved along the optical path, and the polarization state is maintained even when reflected by the reflecting surface. Since it does not change, the amount of current can be accurately measured by measuring the polarization rotation angle of the emitted light.

[0009]

EXAMPLES The magneto-optical element and the current measuring device according to the present invention will be described in detail below. FIG. 1 is a front view of an 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 an electric wire is passed at the time of measuring an electric current is formed in the central portion. Reference numeral 3 is an entrance / exit surface on which a light ray is entered and exited, and 4a, 4b, 4c are reflection surfaces.

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

FIG. 2 is an enlarged sectional view of the reflecting surfaces 4a, 4b, 4c. A multilayer film is formed on the surface (outer surface) of the reflection surface of the medium 1. 4a ₁ is a first dielectric film having a refractive index N ₁ and a thickness D ₁ , and 4a ₂ is a _second dielectric film having a refractive index N ₂ and a thickness D ₂ .
Is a dielectric film. On top of the dielectric films 4a ₁ and 4a ₂ , the same third and fourth dielectric films 4a ₃ and 4a are formed.
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 0} .

The light transmitted through the medium 1 is the 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 on the dielectric film 4a ₂ at an incident angle A ₁ , part of which is reflected by the boundary surface, and part of the light is incident on the dielectric film 4a ₂ . The light incident on the dielectric film 4a ₂ is incident on the dielectric film 4a ₃ at an incident angle A ₂
Is incident on the dielectric film 4a3, part of which is reflected by the boundary surface, and part of which is incident on the dielectric film 4a ₃ . In this way, the light ray that has entered the multilayer film from the medium 1 returns to the medium 1 after repeating the reflection as shown by the dotted optical path. Similar reflection is performed on each reflecting surface.

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

FIG. 3 is a diagram used for designing a magneto-optical element having desired characteristics. The horizontal axis on the right side of _{0 represents} the si of the incident angle A ₀ from the medium 1 to the first dielectric film 4a ₁ .
n value, the vertical axis represents the sin value of the incident angle A ₁ from the _first dielectric film 4a ₁ to the second dielectric film 4a ₂ , and the horizontal axis on the left side from 0 represents the second dielectric film 4a ₂ 3 dielectric film 4a ₃
Is the sin value of the incident angle A ₂ with respect to.

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

In order to satisfy the conditions of the present invention, the incident angle must be outside the semicircle C and inside the rectangle, that is, on the line segments PQ and RS. Therefore,
The incident angle that satisfies 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 and the line segment PQ is X,
When the intersection with the line segment RS is Y, the line segment XY is parallel to the horizontal axis.

FIG. 4 shows a concrete example of the magneto-optical element of the present invention. SF6 is formed on the axially symmetric hexagonal medium 1.
Using glass (refractive index N ₀ = 1.784), a light ray (wavelength λ = 633 nm) is incident at an angle as shown and reflected. Then, as the first (third) dielectric film 4a ₁ , S
iO ₂ (N ₁ = 1.45), second (fourth) dielectric film 4
TiO ₂ (N ₂ = 2.22) is used as a ₂ .

Under this condition, each incident angle is B ₀ = 5
When set to 0 °, B ₁ = 70.7 ° and B ₂ = 37.7 °
Becomes This B ₀ = 50 ° is a boundary reflection surface between the medium 1 and the first dielectric film 4a ₁ , and Brewster angle = 39.1 °,
The critical angle is within the range of 54.4 °. Also, at the boundary reflection surface between the first dielectric film 4a ₁ and the second dielectric film 4a ₂ , B
₁ = 70.7 ° is within the range of Brewster's angle = 56.5 ° and critical angle = 90 °. This result satisfies the required condition shown in FIG.

Further, in the film thickness of each dielectric film, D ₁ = λ / (4N ₁ cosB ₁ ) = 406 nm, D
₂ = λ / (4N ₂ cosB ₂ ) = 111 nm,
Since the optical film thickness of each dielectric film is a quarter wavelength, the partially reflected light at each boundary reflection surface causes a constructive interference effect. For example, when the unit of the dielectric film is 12 pairs, the amplitude reflection coefficient R _s = 1.00000 and R _p = 0.99996, and the polarization-preserving reflection 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. There is. The laser light 15 passes through the polarizer 17 and enters the magneto-optical element 10. As described above, the laser light 15 is internally reflected by each reflection surface in the medium and makes one round, and is emitted 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 the emitted light is transmitted through the analyzer 18 and detected by the detector 19 which is a photoelectric converter. This received light detection amount is proportional to the current amount of the electric wire 16. When 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 transmitting the end face at the time of emission, the measurement sensitivity becomes maximum.

[0021]

According to the present invention, a closed circuit of light can be formed in a medium in which a reflection film that retains polarized light is formed, so that the entire optical path can be made optically isotropic. Further, when such a magneto-optical element is used for current measurement, the current flowing in any direction can be measured very accurately.

[Brief description of drawings]

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

FIG. 2 is an enlarged cross-sectional view of a reflecting surface of the magneto-optical element shown in FIG.

FIG. 3 is a diagram used for designing a magneto-optical element having desired characteristics.

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

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

[Explanation of symbols]

 1 Medium with Magneto-Optical Effect 2 Hole 3 Entrance / Exit Surface 4a, 4b, 4c Reflective Surface 5a Incident Light 5b Exit Light 10 Magneto-Optical Element 12 Hole 15 Laser Light 16 Wire 17 Polarizer 18 Analyzer 19 Detector

Claims (2)

[Claims] 1. A medium made of a material having a magneto-optical effect, wherein light incident on the inside of the medium is reflected by a plurality of reflecting surfaces of the surface and emitted from the vicinity of the incident point, and the reflecting surface is a dielectric. The magneto-optical element which is formed of the multi-layered film and has the refractive index of the medium and the dielectric material and the incident angle set such that the incident angle of light with respect to the reflecting surface is not less than the Brewster angle and not more than the critical angle. 2. The magneto-optical element according to claim 1,
A current path is formed in the space surrounded by the optical path of the light reflected in the medium, the polarization amount of light is changed according to the amount of current flowing through this path, and the current amount is measured from this polarization amount. Current measuring device.