JP3459089B2 - Optical isolator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator and, more particularly, to optical communication and writable using a semiconductor laser having a wavelength range of 0.6 to 1.1 μm as a light source. The present invention relates to an optical isolator for preventing light reflected from an end face of an optical fiber, a lens system, a connector, or the like in a video disk or the like. 2. Description of the Related Art Generally, an optical isolator comprises a magneto-optical crystal plate having a thickness such that a Faraday rotation angle of 45 ° can be obtained between a polarizer and an analyzer whose polarization directions are arranged at 45 ° to each other. The basic configuration is such that an optical element is placed, and a permanent magnet for applying an external saturation magnetic field to the magneto-optical element is arranged around the magneto-optical element. FIGS. 2A and 2B are diagrams showing the principle of an optical isolator. FIG. 2A shows the state of the plane of polarization of light that has entered in the forward direction. Of the incident light 22 that has entered the polarizer 21, the linearly polarized light 24 that has passed through the polarizer 21 is given a 45 ° rotation by the magneto-optical element 25. The linearly polarized light 26 rotated by 45 ° passes through an analyzer 28 whose polarization axis is at 45 ° with respect to the polarization axis of the polarizer 21 and is emitted as emission light 27. The white arrow 29 in the figure indicates the direction of the applied magnetic field. On the other hand, FIG. 2B shows the state of polarization of light (reflected light) incident in the opposite direction. The linearly polarized light 36 from which the reflected light 32 has passed through the analyzer 28 has a non-reciprocal property of the Faraday rotation, so that the Faraday rotation only depends on the direction of the magnetic field indicated by the white arrow 29 irrespective of the light incident direction. The direction of rotation is determined, and the linearly polarized light 34 further undergoes a 45 ° Faraday rotation when passing through the magneto-optical element 25.
Are orthogonal to the polarization direction of the polarizer 21 and cannot pass through the polarizer. Conventionally, this type of optical isolator has a configuration as shown in FIG. In FIG. 3, a magneto-optical element 25 is arranged between a polarizer 21 and an analyzer 28, a permanent magnet 30 for applying a saturation magnetic field to the magneto-optical element is arranged, and housed in a case 31. [0006] Incident light 22 from a light source such as a semiconductor laser
Are transmitted through the optical isolator and become outgoing light 27. The output light includes a polarizer 21, a magneto-optical element 25, and an analyzer 28.
Are all arranged in parallel with the light entrance / exit surface of the case 31. [0007] The magneto-optical element conventionally used is not limited to a specific orientation and can be used as it is arbitrarily cut because the magneto-optical single crystal used is optically isotropic. . [0008] [Problems that the Invention is to Solve magneto-optical element used in the optical isolator _{Cd 1-x-y Mn x} Hg y T
_{e, Cd 1-x-y} -z Mn x Hg y Zn z Te, Cd
The _{1-x-y Mn x Zn} y Te, generally, is produced in flux method from Bridgman method or Te melt. However, with the composition (x ≧ 0.1, x + y + z = 1) blended with a high Mn concentration, the experimental fact that twins tended to be confirmed was confirmed. This twin is a phenomenon that is remarkably observed in a compound semiconductor based on group 2-6, and is generally considered to easily occur in a compound semiconductor having a property of low thermal conductivity. In addition, the twin crystal becomes a bottleneck, so that the insertion loss with respect to the laser is small, and a crystal quality that can ensure high isolation cannot be obtained. In addition, lead glass or the like is used for the optical isolator in the wavelength region (0.6 to 1.1 μm) because there is no suitable material. However, the use of a multiple reflection method to compensate for the lack of the material's own Verdet constant results in a complicated structure. As a result, the cost is high and the use is limited to a special measuring instrument. Since the optical isolator in this wavelength region cannot find an excellent magneto-optical element [small size, can be made into an LD module, practical performance (insertion loss: <1 dB, isolation:> 30 dB), good transmitted wavefront quality] Practical application was not advanced to the mass production level. Therefore, the technical problem of the present invention is that Cd
_{1-x-y Mn x Hg} y Te, Cd 1-x-y-z Mn
_{x Hg y Zn z Te, Cd} 1-x-y Mn x Zn y Te
An object of the present invention is to provide an optical isolator using a magneto-optical element in a wavelength region (0.6 to 1.1 μm) in a single crystal. SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and a polarizer and an analyzer having polarization directions arranged at 45 ° to each other, and the polarizer and the analyzer. In an optical isolator composed of a magneto-optical element disposed between a photon and a magnet disposed around the magneto-optical element to saturate the magnetization of the magneto-optical element, a wavelength region (0.6 to a magneto-optical element used in _{1.1μm) Cd 1-x-y} Mn x Hg y Te, Cd
_{1-x-y-z Mn} x Hg y Zn z Te, Cd
Consists _{1-x-y Mn x Zn} y Te single crystal plate, the light incident surface and the light exit surface of the magneto-optical element is an optical isolator, which is a single crystal {111}. In the present invention, the magneto-optical single crystal Cd _1-xy M
_{n x Hg y Te, Cd 1} -xyz Mn x Hg y Zn z Te, Cd
_{1-xy Mn x Zn y Te} (x ≧ 0.1, x + y + z = 1) in uses a crystal plate having a plane parallel to the crystal plane {111}. The reason is as follows. As described above, the magneto-optical single crystal used for this magneto-optical element is generally produced by a Bridgman method or a flux method from Te melt. However, the composition (x ≧ 0.1,
In x + y + z = 1), an experimental fact that twins tend to occur was confirmed. The present inventor has found that when considered as an optical isolator material, the Verdet constant is not significantly affected by twinning. However, it was confirmed that the isolation (extinction ratio) was significantly affected by twinning. That is, the influence of twinning hindered practical application. In addition, when the twin plane exists in the plane, there is a problem that the roughness becomes clear along the twin boundary during polishing processing, and a sufficient transmitted wavefront quality cannot be secured. It has been found that this twin has a regular structure in which stripes are stacked vertically in the [111] direction. According to a study by the present inventors, when light enters parallel to a twin boundary, birefringence occurs and the isolation (extinction ratio) is reduced to 10 to 20 dB. When the boundary between twins was inclined in the light incident direction, the isolation (extinction ratio) gradually improved. In particular, when light enters the twin boundaries vertically,
The isolation (extinction ratio) achieved a practical level of 40 dB. Also, in this case, there is no unevenness along the twin boundary during polishing, and a sufficient transmitted wavefront quality can be ensured. That is, the twin is a stripe pattern perpendicular to the [111] direction. Utilizing the property of having a regular structure in which is stacked, has a small insertion loss with respect to a practically useful laser, and is an excellent magneto-optical element (Cd
_{1-x-y Mn x Hg} y Te, Cd 1-x-y-z Mn
_{x Hg y Zn z Te, Cd} 1-x-y Mn x Zn y T
e) It is possible to provide a wavelength region (0.6 to 1.1 μm) optical isolator using a single crystal. Hereinafter, the present invention will be described with reference to examples. FIGS. 1 (a), 1 (b), 1 (c) and 1 (d)
Magneto-optical single crystal _{(Cd 1-xy Mn x Hg} y Te: x = 0.1
5, y = 0.15) is cut out in a specific direction, and a figure of a magneto-optical element manufactured by optically polishing a specific crystal plane as a light incident surface and a light output surface is shown. The twin has a regular structure in which striped patterns are stacked at intervals of 10 to 1000 μm perpendicular to the [111] direction. FIG. 1A shows the (110) plane. FIG. 1B shows the (100) plane. FIG. 1 (c)
Indicates a (111) plane. FIG. 1D shows a randomly cut surface. [0020] Table 1, the optical isolator configuration shown in FIG. 3, the magneto-optical element _{(Cd 1-x Mn x Hg} y Te single crystal: x
= 0.15, y = 0.15), and FIG.
(B), (c), and (d) are employed to produce an optical isolator as shown in FIG. 3 and to measure the isolation (extinction ratio). The measurement conditions were as follows: sample thickness = 3 mm, measurement wavelength = 0.980 μm, beam diameter = 1 m
mφ, measurement temperature = 25 ° C. [Table 1] The magneto-optical device (Cd
_1-xy Mn _x Hg _y Te single crystal: x = 0.15, y = 0.1
The result of measuring the isolation (extinction ratio) characteristics when the optical isolator as shown in FIG. 3 is manufactured using 5) will be described. First, for comparison, a case where an optical isolator is manufactured by a conventional method and the isolation is measured will be described. Conventional methods are shown in FIGS. 1 (a), (b),
A magneto-optical element (Cd having the crystal orientation shown in FIG.
_1-xy Mn _x Hg _y Te single crystal, x = 0.15, y = 0.1
This corresponds to the case where an optical isolator is manufactured using 5). At that time, the spot of the light source hits a boundary surface between many twins, and birefringence occurs. As a result, the isolation required for the optical isolator cannot be obtained in any case. FIG. 4A shows a transmitted wavefront of a surface polished on the (110) plane in the conventional method. (B) shows the transmitted wavefront of the surface polished with the (111) plane of the present invention. In the conventional method, it can be seen that the wavefront is distorted corresponding to the twin. In the embodiment of the present invention, FIG. 1 (c) is used so that the light source illuminates the twin boundaries at right angles so that the spot of the light source hits a large number of twin boundaries and no birefringence occurs. (Cd _1-xy Mn _x Hg _y)
An optical isolator was manufactured using a Te single crystal, x = 0.15, y = 0.15). When the isolation (extinction ratio) of the optical isolator was measured, the isolation required for the optical isolator (> 40 dB) was obtained.
When the state of the transmitted wavefront was measured, there was no practical problem [see FIG. 4 (b)]. Note that Cd
_{1-x-y-z Mn} x Hg y Zn z Te, Cd
_{1-x-y Mn x Zn} y Te Cd 1-x-y M In the case of
It is similar to the n _x Hg _y Te. As described above, according to the present invention,
An optical isolator using a magneto-optical element used in a wavelength region (0.6 to 1.1 μm) can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] magneto-optical element _{(Cd 1-xy Mn x Hg} y Te single crystal, x = 0.15, y = 0.15 ) between the crystal surface and the twin boundary surface of The figure which shows a relationship. FIG. 1A shows a crystal plane {110},
FIG. 1B is a diagram illustrating a crystal plane {100}, FIG. 1C is a diagram illustrating a crystal plane {111}, and FIG. 1D is a diagram illustrating a relationship between a random plane and a twin boundary. FIG. 2 is an explanatory diagram showing the principle of an optical isolator. FIG.
2A is a diagram illustrating incident light, and FIG. 2B is a diagram illustrating reflected light. FIG. 3 is a configuration diagram of an optical isolator. FIG. 4 is a view showing a transmitted wavefront image taken at a measurement wavelength λ = 0.85 μm. FIG. 4A is a diagram illustrating a case where light is incident on a crystal plane {110}, and FIG. 4B is a diagram illustrating a case where light is incident on a crystal surface {111}. [Description of Signs] 1, 2, 3, 4, 25 Magneto-optical elements 1a, 2a, 3a, 4a Twin boundary surface 21 Polarizer 22 Incident light 24, 26, 34, 36 Linear polarized light 27 Transmitted light (emitted light ) 28 analyzer 29 arrow indicating the direction of the magnetic field 30 permanent magnet 31 case 32 reflected light (return light)

Continuation of front page       (56) References Japanese Journal               of Applied Physic               s, Vol. 30, No. 2A pp. L               198-L201 (1991)                 ИзвестяВ. У. З. "ФИЗ               ИКА "NO. 3 pp. 96−97               (1990) (Izvestia Vuz               of, Physics)

Claims (1)

(57) Claims 1. A polarizer and an analyzer having polarization directions arranged at 45 ° to each other, a magneto-optical element arranged between the polarizer and the analyzer, and In an optical isolator including a magnet disposed around the magneto-optical element to saturate the magnetization of the optical element, a wavelength region (0.6 to
The composition formula is C as a magneto-optical element used for 1.1 μm).
_{d 1-x-y Mn x} Hg y Te, Cd 1-x-y-z M
n _x Hg _y Zn _z Te, or _{Cd 1-x-y Mn x} Z
It is n y _Te made of single-crystal plate, optical isolator, wherein the light incident elevation surface and the light exit surface of the magneto-optical element is a crystal plane {111}.