Magneto-optics in Diluted Magnetic Semiconductors and in Ferromagnetic-Metal/Semiconductor Hybrids
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Magneto-optics in Diluted Magnetic Semiconductors and in FerromagneticMetal/Semiconductor Hybrids V. Zayets1 , M. C. Debnath1,2, H. Saito1, S. Yuasa1, and K. Ando1 1 Spintronics Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Umezono 1-1-1, Tsukuba, Ibaraki-ken 305-8568, Japan. 2 University of Oklahoma, 440 West Brooks, Norman, OK 73019-2061, U.S.A ABSTRACT The optical isolator made of diluted magnetic semiconductor and the isolator made of a ferromagnetic-metal/semiconductor hybrid have been developed aiming to integrate nonreciprocal optical devices, such as an optical isolator and optical circulator, into the semiconductor-made optoelectronic integrated circuits,. The Cd1-xMnxTe exhibits a huge Faraday effect and can be grown on a semiconductor substrate. For Cd1-xMnxTe waveguide with a Cd1xZnxTe/ Cd1-xMnxTe quantum well grown on GaAs substrate we achieved a high Faraday rotation of 2000 deg/cm, a high isolation ratio of 27 dB, a low optical loss of 0.5 dB/cm, and a high magneto-optical figure-of-merit of 2000 deg/dB/kG in a wide 25-nm wavelength range. It was predicted theoretically and proved experimentally the effect of non-reciprocal loss in hybrid semiconductor/ferromagnetic metal waveguides. This effect can be use for new design of waveguide optical isolator. Because of its simplicity and technological compatibility, this design is attractive for the integration into optoelectronic integrated circuits. The magneto-optical figure-of merit of 7% was demonstrated for the AlGaAs passive optical waveguide covered by Co. INTRODUCTION Magneto-optical (MO) materials are unique, because of their non-reciprocal properties. The time inverse symmetry is broken in magneto-optical materials. Therefore, the properties of magneto-optical materials are different for two opposite directions of light propagation and optical non-reciprocal devices like the optical isolator and the optical circulator can be fabricated only by utilizing magneto-optical materials. The optical isolator is an important component of optical networks. It is transparent in one direction and blocks light in opposite direction. Due to the imperfect matching between optical components in the network, the unwanted back reflection always exists and it severely disturbs the network performance. The stable and reliable operation of the optical network can be only achieved in the case when the optical components are protected by an optical isolator. For example, the amplification in long-distance optical link by serially-connected optical amplifiers is practically impossible without the use of isolators, because of gain-saturation of the amplifiers by back-traveling amplified spontaneous emission. At present, there is an industrial demand to integrate all optical components into an optoelectronics chip. Because of compactness, the problem of unwanted reflection is more severe for the integrated circuits. Therefore, the integration of the isolator into the circuit is important in order to achieve the performance compar
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