A new Bi-substituted rare-earth iron garnet for a wideband and temperature-stabilized optical isolator
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Shouye Zhang Materials Science & Engineering Department and State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, People’s Republic of China (Received 26 March 1999; accepted 22 February 2000)
A wideband and temperature-stabilized optical isolator for 1.55-m wavelength was developed using a new Bi-substituted holmium–ytterbium ion garnet (HoYbBiIG) single crystal as a Faraday rotator. The optical isolator features 0.34-m bandwidth, less 0.6 dB insertion loss and over 37 dB backward loss at a wavelength of (1.55 ± 0.17) m throughout the temperature range from −10 to 60 °C. The Faraday rotation and optical absorption loss of HoYbBiIG were investigated in the near-infrared wavelength region ( ⳱ 0.9 to 1.7 m). The specific Faraday rotation of Ho0.85Yb1.02Bi1.13Fe5O12 is about −767°/cm at ⳱ 1.55 m. The Faraday rotation wavelength and temperature characteristics of HoYbBiIG crystals are also discussed. These results indicate that the Bi-substituted holmium–ytterbium iron garnet single crystals realize a high Faraday rotation stability against temperature and wavelength in the near-infrared region.
I. INTRODUCTION
The performance and lifetime of lasers can be degraded by backreflections into the laser cavity. An optical isolator is a passive and nonreciprocal device that can eliminate such deleterious feedback effects.1 Optical isolators yield more reliable performance from the laser in use, including longer lifetime, increased frequency stability, side-mode suppression, and steadier power output. Isolators can also protect one laser from others in the system, as in an erbium-doped fiber amplifier (EDFA), in which the source laser must be shielded from the pump laser and vice versa. In recent years, growing attention is being focused on wavelength division multiplexing optical communication system as a promising means of mass-scale communication. To realize these systems, wideband and temperature-stabilized optical isolators are essential, which in turn require Faraday rotators capable of ensuring a Faraday rotation (FR) stable against wavelength and temperature variation. In the near-infrared wavelength range, yttrium iron garnet (Y3Fe5O12 or YIG) and bismuth-substituted garnet films or bulk single crystals such as gadolinium– bismuth iron garnet (Gd3−x Bix Fe5O12 or GdBiIG) are often used as Faraday rotators. However, their shortcoma)
e-mail: [email protected] J. Mater. Res., Vol. 15, No. 8, Aug 2000
http://journals.cambridge.org
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ing is apparent: the FR coefficient F of YIG is too small for practical use; FR of Bi-substituted garnet reveals wavelength and temperature dependencies.2 As a solution to this problem, we have proposed a new idea to find a new Bi-substituted magneto-optical material for wideband and temperature-stabilized optical isolators by combination of two types of Bi-substituted rare-earth iron garnets with different signs for the temperature and wavelength coefficients of the FR. The FR coefficient F of Yb3Fe5O12 has been reported to
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