JP2841260B2 - Magneto-optical element - 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 used as an optical isolator such as an optical amplifier, and more particularly to a magneto-optical device suitable for use in a wavelength region of substantially 0.98 .mu.m.

[0002]

2. Description of the Related Art Heretofore, 1.
The 5 μm band traveling wave type optical amplifier has characteristics of high efficiency, no polarization dependency, and excellent matching with the transmission system. From a practical viewpoint, a laser diode using a 0.98 μm and 1.48 μm band ( Hereafter, LD) excitation is actively studied. As a result of experimentally examining the signal light gain and noise characteristics, it has been found that 0.98 μm band pumping has higher efficiency and lower noise characteristics than 1.48 μm band pumping. However, at present, the development of an optical amplifier having an optical device (such as an optical isolator) suitable for the 1.48 μm band is progressing.

[0003]

At present, an optical isolator using a terbium gallium garnet (TGG) single crystal has been put into practical use as a 0.98 μm optical isolator. However, since the dimensions are too large compared to LDs, they have not been studied from a future perspective. In addition, bulk yttrium / iron / garnet (YIG) and Bi
The substituted garnet has a large absorption in the 0.98 μm band, and thus has a transmission loss of about 5 dB, which is not practical. C in which a part of Cd of CdTe having a ZnS type crystal structure is substituted with Mn
d _1-x Mn x Te is a material having a large Verdet constant, practical performance is confirmed as an optical isolator material for visible light wavelength 0.85～0.63Myuemu {Onodera, Oikawa: 15th Magnetics Society of Japan Academic Lecture summary 30aB-7,
p179 (1991)｝.

However, at 0.98 μm, the Verdet constant is too small, and practical use has been difficult.
That is, L used for the 0.98 μm band pumping optical amplifier
The fact that there is no real optical isolator that can be made into a D module is essentially 1.48μ in high efficiency and low noise characteristics.
This was one of the factors behind the delay in practical application development despite being superior to m-band excitation.

Accordingly, it is an object of the present invention to provide a magneto-optical element suitable for use in a wavelength region of substantially 0.98 μm in view of the above-mentioned drawbacks.

[0006]

According to the present invention SUMMARY OF], have _{Cd 1-x -y Mn x Hg} y Te single crystal obtained by mixing Mn and Hg, substantially used in the wavelength region of 0.98μm A magneto-optical element having possible characteristics, wherein the single crystal is M
In nTe-HgTe-CdTe quasi ternary phase diagram, surrounded _{Mn 0.01 Hg 0.04 Cd 0.95 Te,} Mn 0.01 Hg 0.1 Cd 0.89 Te, Mn 0.12 Hg 0.17 Cd 0.71 Te, Mn 0.25 Hg 0.04 Cd 0.71 Te, the four points Thus, a magneto-optical element characterized by having a composition falling within the range described above is obtained.

Further, according to the present invention, there is provided an optical isolator including the magneto-optical element as a Faraday rotator.

[0008]

Cd _1-x Mn _x Te where a part is substituted with Mn of CdTe and Cd with [action] ZnS-type crystal structure of a material having a large Verdet constant, optical isolator materials for visible light wavelength 0.85~0.63μm As described above, practical performance was not confirmed in the 0.98 μm band because the Verdet constant was small. This is because there is a feature that the Verdet constant increases near the light absorption edge. Therefore, in order to obtain practical performance using this material, it is only necessary to consider adjusting the band gap energy of the material and selecting the Mn composition so as to increase the absolute value of the Verdet constant. In order to shift the band gap energy to the 0.9 μm band, Cd may be partially replaced with Hg. Eventually,
The bulk crystallinity has a significant effect. Therefore, an optimum crystal composition is determined in consideration of crystallinity.

According to the magneto-optical device of the present invention, an LD module having practical characteristics of an isolation of 30 dB or more and an insertion loss of 1 dB or less is 0.98 μm.
An m-band optical isolator can be obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magneto-optical device according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

First, the selection of the optimum composition will be described.

Crystals of various compositions in the phase diagram of the MnTe-HgTe-CdTe pseudo-ternary system were prepared by the Bridgman method. Cd, Mn, Te, and Hg were compounded in a quartz ampoule at respective composition ratios and sealed in a vacuum. If not completely melted at the time of heating, the quartz ampule may be cracked due to an increase in vapor pressure. Therefore, the quartz ampule is required to have a sufficient thickness and to have a Te excess composition of about 80%.
A melting point of about 0 ° C. is used to reduce the internal pressure in the growing process.

The quartz ampoule was placed in a vertical Bridgman furnace and maintained at a melting temperature of 800 ° C. for 10 hours. Then, the quartz crucible was gradually lowered, and crystallized from one end of a low-temperature portion of the quartz ampule.

FIG. 1 shows that when an applied magnetic field of 3000 Oe capable of realizing an optical isolator (9.5 φ × 10 Lmm) that can be made into an LD module is applied, the isolation becomes 30
This shows a composition that can realize an insertion loss of 1 dB or less and a loss of 1 dB or more. As shown in FIG. _{1, Cd 1-x -y Mn} x Hg y Te single crystal constituting the magneto-optical device according to the present invention, MnTe
-HgTe-CdTe pseudo ternary phase diagram, Mn _0.01
Hg _0.04 Cd _0.95 Te, Mn _0.01 Hg _0.1 Cd _0.89 T
e, Mn _0.12 Hg _0.17 Cd _0.71 Te, Mn _0.25 Hg _0.04
It has a composition included in a range surrounded by four points of Cd _0.71 Te.

An embodiment of the present invention will be described below.

Example 1 A single crystal having a composition of Mn _0.1 Hg _0.1 Cd _0.8 Te was
e The material was grown by the Bridgman method at a low melting temperature (800 ° C.) by making the melt excessive. The breeding method is as described above. From the grown single crystal, a square plate-shaped sample of 2 mm × 2 mm × 1.7 tmm was prepared such that the {111} plane was an end face. When a magnetic field of 3000 Oe was applied, 45 ° Faraday rotation was obtained with respect to a laser beam having a wavelength of 0.98 μm, isolation: 30 dB, insertion loss: 0.7 dB, size of the isolator: φ8 × 5 Lm
It has been clarified that m can be used sufficiently as an optical isolator.

Example 2 A single crystal having a composition of Mn _0.05 Hg _0.05 Cd _0.9 Te
e By growing the melt in excess, it was grown by the Bridgman method at a low melting temperature (850 ° C.). The breeding method is as described above. From the grown single crystal, a square plate-shaped sample of 2 mm × 2 mm × 2.5 mm was prepared such that the {111} plane was an end face. When a magnetic field of 5000 Oe was applied, a wavelength of 0.
A 45 ° Faraday rotation is obtained for 98 μm laser light, isolation: 30 dB, insertion loss:
0.7dB, isolator size: φ13 × 10Lm
It has been clarified that m can be used sufficiently as an optical isolator. However, it is slightly larger than a semiconductor laser when viewed from the intended use.

Comparative Example A single crystal having a composition of Mn _0.03 Hg _0.00 Cd _0.97 Te
e Grew by the Bridgman method at low melting (1000 ° C.) by making the melt excessive. The breeding method is as described above. A square plate sample of 2 mm × 2 mm × 7.0 mm was prepared from the grown single crystal such that the {111} plane was an end face. When a magnetic field of 5000 Oe is applied, the wavelength becomes 0.9.
A 45 ° Faraday rotation is obtained for 8 μm laser light, isolation: 25 dB, insertion loss:
1.0dB, isolator size: φ13 × 15Lm
m. The performance is insufficient for the intended use, and is larger than a semiconductor laser from a practical point of view.

[0019]

As described above, according to the present invention,
It is possible to provide a magneto-optical element suitable for use as an optical isolator substantially in a wavelength range of 0.98 μm.

[Brief description of the drawings]

FIG. 1 shows a crystal composition that can realize an optical isolator capable of forming an LD module in the present invention is MnTe-HgTe.
FIG. 3 is a diagram represented by a CdTe pseudo-ternary phase diagram.

Claims (2)

(57) [Claims] 1. Cd _{1-x -y} containing Mn and Hg
Mn _x Hg _y Te single crystal, substantially 0.98 μm
Wherein the single crystal is MnTe-HgTe-CdTe pseudo-3.
In the original system diagram, the composition included in the range surrounded by the four points of Mn _0.01 Hg _0.04 Cd _0.95 Te, Mn _0.01 Hg _0.1 Cd _0.89 Te, Mn _0.12 Hg _0.17 Cd _0.71 Te, Mn _0.25 Hg _0.04 Cd _0.71 Te, A magneto-optical element comprising: 2. An optical isolator comprising the magneto-optical element according to claim 1 as a Faraday rotator.