Optical: systems and elements – Optical modulator – Having particular chemical composition or structure
Patent
1994-09-15
1997-01-21
Ben, Loha
Optical: systems and elements
Optical modulator
Having particular chemical composition or structure
359321, 359257, 359484, 359497, 372 37, G02F 100
Patent
active
055964478
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a magnetooptical element for use as an optical isolator in an optical amplifier or the like and, more particularly, to a magnetooptical element which is suitable for use in a wavelength range between 0.8 micrometer and 1.1-micrometers. This invention relates furthermore to an optical isolator in which the magnetooptical element is used as a Faraday rotator.
BACKGROUND ART
A travelling-wave optical amplifier of a 1.5-micrometer band with an Er (erbium) added optical fibre has a high efficiency, no polarization dependency, and an excellent feature of match with a transmission system. Its practical application to excitation of laser diodes (hereafter LD) of a 0.98-micrometer and 1.48-micrometer bands has vigorously been studied. As a result of experimental studies of signal-to-optical gain and noise characteristics, it is already known that higher-efficiency and lower-noise characteristics are achieved by the excitation in the 0.98-micrometer band than the excitation in the 1.48-micrometer band. Development is, however, currently in progress as regards an optical amplifier comprising an optical device (as, for example, an optical isolator) suitable in the 1.48-micrometer band.
As a 0.98-micrometer optical isolator, optical isolators are in practical use at present with use of a terbium-gallium-garnet (TGG) single crystal. They are too bulky as compared with an LD and are not studied for future points of view. Bulk yttrium-iron-garnet (YIG) and Bi-substituted garnet are highly absorbing at the 0.98-micrometer band and are not practical because of an insertion loss of about 5 dB. It has been confirmed that Cd.sub.l-x Mn.sub.x Te is a material having a great Verdet constant and is confirmed to exhibit a practical performance as a material for optical isolators of visible wavelengths of 0.85 to 0.63 micrometer when Mn is substituted for a part of Cd of CdTe of a ZnS crystal structure (Onodera and Oikawa, the 15-th Scientific Lecture Proceedings of the Applied Magnetism Institute of Japan, 30aB-7, page 179 (1991)).
The Verdet constant is, however, too small at 0.98 micrometer and has made it difficult to use in practice. This has been a main reason of a delay in development of an optical isolator for 0.98-micrometer band excitation of LD-moduled optical amplifier despite its intrinsically higher efficiency and lower noise characteristics than 1.48-micrometer band excitation.
It is therefore an object of this invention to provide a magnetooptical element suitable for use in a wavelength range between 0.8 micrometer and 1.1 micrometers (above all, 0.98 micrometer).
It is another object of this invention to provide an optical isolator in which use is made as a Faraday rotator of the magnetooptical element of the type described.
DISCLOSURE OF THE INVENTION
According to a first aspect of this invention, there is provided a magnetooptical element which comprises a single crystal of Cd.sub.l-x-y Mn.sub.x Hg.sub.y Te including Mn and Hg and which is charaterized in that so as to be operable in a wavelength range between 0.8 micrometer and 1.1 micrometers the single crystal has a composition in an area defined in a quasi three-element phase diagram of MnTe--HgTe--CdTe by four points of: Te, Mn.sub.0.12 Hg.sub.0.17 Cd.sub.0.71 Te, and Mn.sub.0.25 Hg.sub.0.04 Cd.sub.0.71 Te.
According to a second aspect of this invention, there is provided a magnetooptical element which comprises a single crystal of Cd.sub.l-x-y Mn.sub.x Hg.sub.y Te including Mn and Hg and which is characterized in that so as to be operable in a wavelength range between 0.8 micrometer and 1.1 micrometers the single crystal has a composition in an area defined in a quasi three-element phase diagram of MnTe--HgTe--CdTe by four points of: Te, Mn.sub.0.45 Hg.sub.0.25 Cd.sub.0.3 Te, and Mn.sub.0.48 Hg.sub.0.2 Cd.sub.0.32 Te.
According to this invention, there is furthermore provided an optical isolator characterized in that use is made as a Faraday rotator of the magnetooptical element according to the above-recite
REFERENCES:
patent: 3586416 (1971-06-01), De Betetto
patent: 3947089 (1976-03-01), Rapp
patent: 4933629 (1990-06-01), Kozuka et al.
patent: 4988170 (1991-01-01), Buhrer
patent: 5027367 (1991-06-01), Rea, Jr. et al.
patent: 5043996 (1991-08-01), Nilsson et al.
Japanese Journal of Applied Physics vol. 30 No. 2A Part 02 (Jan. 2, 1991) pp. L198-L201.
Japanese Citation (Onodera and Oikawa) The 15th Scientific Lecture Proceedings of the Applied Magnetism Institute of Japan (p. 179)-1991.
Ben Loha
Tokin Corporation
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