JP2985022B2 - Magneto-optical element and optical isolator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a short wavelength (0.6 to 0.8)
The present invention relates to a magneto-optical element used for a Faraday rotator of an optical isolator and an optical isolator using the same.

[0002]

2. Description of the Related Art It has been proposed to use an optical isolator for removing return optical noise in optical communication, optical measurement, magneto-optical disk systems and the like using a short wavelength (0.6 to 0.8 .mu.m band) semiconductor laser or the like as a light source. ing. Optical isolator has a structure sandwiching axially Faraday rotator with deflectors及検photons, the use of semi-magnetic semiconductor _{Cd 1-x Mn x Te (} 0 <x ≦ 1) as a Faraday rotator material Are being considered.

[0003]

Generally, Cd _1-x Mn
_An xTe (0 <x ≦ 0.7) single crystal is produced by solidification from a liquid phase by the Bridgman method, but it is known that twin defects are generated. When a crystal having such twin defects is used as a Faraday rotator, a problem arises in that sufficient quenching characteristics cannot be obtained. The generation of this twin defect is attributed to the phase transformation of the substance, and it is described that a twin defect is generated at the time of a phase transition from a hexagonal crystal, which is a high-temperature phase, to a cubic crystal, which is a low-temperature phase. Recently, the THM method (Travelling Heater Method), in which the cubic crystal is grown directly by setting the melting point below the phase transformation temperature using Te as a solvent.
Has been proposed, and it has become possible to grow crystals without twin defects.
However, at present, the THM method has a growth rate of 1/10 or less of that of the Bridgman method, and is expensive and has not reached mass production level because it is difficult to produce a large single crystal. It was a situation.

[0004] Therefore the technical problem of the present invention was made by better Bridgman method in productivity Cd _1-x Mn _x Te
It is an object of the present invention to provide a Faraday rotator material that is crystallized and has practically sufficient extinction characteristics, and an optical isolator using the same.

[0005]

Since the Verdet constant of the problem-solving means for the] Cd _1-x Mn _x Te crystal does not depend on the orientation of the crystal plane through which light enters, conventionally constituted the Faraday rotator in any plane . However, the twin defects generated in the crystal have a regular structure in which twin planes are stacked perpendicular to the [111] direction. The present inventors have experimentally found that the extinction characteristic of a crystal depends on the crystal orientation, and have accomplished the present invention.

According to the present invention, a vertical wall open surface in twin planes of the grown _{(Cd 1-x Mn x Te} (0.1 ≦ x ≦ 0.7) single crystal by the Bridgman method {110 According to the present invention, there is provided a magneto-optical element characterized in that a laser beam is made to be incident perpendicularly to the｝ plane.
An optical isolator characterized in that a maximum extinction azimuth in a {110} plane of the magneto-optical element is defined as an extinction axis, and a polarization direction of a polarizer or an analyzer is inclined by 22.5 degrees with respect to the extinction axis. Is obtained, and a quenching characteristic sufficient for practical use can be ensured with a crystal having twin defects.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, linear polarization 1 was perpendicularly incident on the crystal plane 2, the polarization azimuth θ was changed, and the extinction ratio was measured without applying a magnetic field. The extinction ratio I [dB: decibel] is defined by I = −10 loy10 (intensity of transmitted light at the time of extinction / intensity of incident light). The result is as shown in FIG.

In FIG. 2, the extinction ratio fluctuates with a period of θ of 90 °. The magnitude of the fluctuation is largest in the {110} plane which is perpendicular to the twin plane or the cleavage plane shown by the curve 21, and is an arbitrary plane except for the {110} plane and the {111} plane which is the twin plane (curve 21). In 23), the fluctuation is minimized, but the peak value of the extinction ratio is reduced. The extinction axis at which the extinction ratio is maximized exists in the {111} plane (curve 22) and the {110} plane. That is, birefringence is caused in the originally optically isotropic crystal by the influence of twin defects. $ 11 to get high extinction ratio
The extinction axis of the {1} or {110} plane may be used. However, in the case of a Faraday rotator of an optical isolator, the polarization vector of the return light is rotated by 45 degrees, so that the light passes through the area of ± 22.5 degrees from the extinction axis Will be. In this regard, it is most advantageous to use the {111} plane of the crystal. However, since the crystal by the Bridgman method grows in the <110> direction, the grown crystal ingot has the orientation shown in the perspective view of FIG. 3A and the side view of FIG.
The processing of the {1} plane has the following disadvantages compared to the {110} plane. In FIGS. 3A and 3B,
The cutting of the {111} plane indicates that the ingot is to be made perpendicular to the growth plane, and the {110} plane is to be sliced in parallel to the growth plane. Since the {110} plane is an open wall, it is not necessary to determine the orientation. However, the {111} plane requires the orientation. At present, an etching solution effective for a crystal having a high concentration (x> 0.5) is not known, and it is not easy to determine the orientation.
As shown in FIG. 3 (b), the cutting 33 of the {111} plane cuts the crystal ingot perpendicular to the growth plane, so that a wafer of the same size cannot be cut out. Further, since the wall is opened perpendicular to the wafer, the yield is likely to be reduced due to breakage in the cutting and polishing steps. On the other hand, in the case of the cutting of the {110} plane in FIG. 9B, a wafer having the same diameter can be cut out to cut the ingot. Further, since the wall of the wafer is not opened, the yield in the cutting and polishing steps is high. Therefore, the {110} plane is more advantageous than the {111} plane for mass production, and practically sufficient extinction characteristics can be obtained even with the {110} plane.

Next, a specific example of manufacturing a magneto-optical element according to an embodiment of the present invention will be described. Composition C by Bridgman method
and growing a single crystal of _{d 1-x Mn x Te (} x = 0.2,0.5). These crystals had a structure in which twin planes overlapped at about 10 μm intervals in the <111> direction. {111} plane parallel to the twin plane and {110} which is a wall open plane perpendicular to the {111} plane
A Faraday rotator having a Faraday rotation angle of 45 degrees was formed by cutting out a surface and an arbitrary surface other than the above, applying an antireflection film after optical polishing and applying a magnetic field of 2000 Gauss. When x = 0.5, the wavelength is 633 nm, x =
The one with 0.2 was a 780 nm Faraday rotator.
With respect to the Faraday rotators of the {111} plane and the {110} plane, the polarization direction of the analyzer is set at 22.5 degrees from the extinction axis of the crystal, and 6 degrees.
Arranged at an arbitrary angle of 7.5 degrees for comparison. 22.5
In the case of degrees, the deflection vector causing a 45 degree Faraday rotation is set within 22.5 degrees from the main axis, and in the case of 67.5 degrees, the deflection vector is set so as to be between 22.5 degrees and 45 degrees from the main axis. Further, for the Faraday rotator on an arbitrary surface, the polarization direction of the analyzer is arbitrarily arranged so as to obtain the maximum extinction ratio. Tables 1 and 2 show the results of measuring the extinction ratio of the Faraday rotator having such a configuration. In Table 1, Table 1 shows the extinction ratio at a wavelength of 780 nm when using a crystal having a composition x = 0.2, and Table 2 shows the extinction at a wavelength 633 nm when using a crystal having a composition x = 0.5. Shows the ratio. As shown in Tables 1 and 2, in the case of a Faraday rotator in which the polarization direction of the analyzer is tilted by 22.5 degrees from the extinction axis on the {110} plane, the extinction ratio satisfies a practically necessary level of 40 dB. .

[0010]

[Table 1]

[0011]

[Table 2]

[0012]

As described above, according to the present invention, a Faraday rotator material for an optical isolator having good extinction characteristics and an optical isolator using the same can be provided at low cost.

[Brief description of the drawings]

FIG. 1 shows a method for measuring an extinction ratio of a magneto-optical element according to an embodiment of the present invention.

FIG. 2 is a diagram showing the polarization azimuth dependence of a magneto-optical element according to an example of the present invention.

FIG. 3A is a perspective view showing the orientation of a crystal ingot grown by the Bridgman method. (B) is a side view of the crystal ingot of (a), showing a cutting direction.

[Explanation of symbols]

1 the incident light 2 optical surface 3 the polarization direction 4 the emitted light 10 Cd _1-X Mn curve of X Te 21 {110} plane curve 23 any surface curve 22 {111} plane of the

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G02F 1/09-1/095 C30B 29/52 G02B 27/28 CA (STN) JICST file (JOIS)

Claims (2)

(57) [Claims] Cadmium produced by the Bridgman method used for incident light in a wavelength band of 0.6 to 0.8 μm.
Manganese telluride _{Cd 1-x Mn x Te (} 0.1 ≦ x ≦
0.7) A magneto-optical element made of a single crystal, wherein the single crystal has a {110} plane as an incident surface for the incident light. 2. The extinction axis is defined as the maximum extinction azimuth in the {110} plane of the magneto-optical element according to claim 1, and the polarization direction of a polarizer or an analyzer is inclined by 22.5 degrees with respect to the extinction axis. An optical isolator characterized by: