Hybrid semiconductor-ferromagnetic-metal active optical isolator.
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J4.6.1
Hybrid semiconductor-ferromagnetic-metal active optical isolator. Vadym Zayets and Koji Ando Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Umezono 1-1-4, Tsukuba, Ibaraki 305-8568, Japan. ABSTRACT
The effect of non-reciprocal loss/gain in semiconductor-ferromagnetic-metal hybrid was studied. It is shown that the optical loss/gain of this semiconductor-ferromagnetic-metal hybrid differs for the forward and backward propagation when the magnetization is perpendicular to the light propagation and lies in the film plane. Using this effect a new design of optical isolator is proposed, which is beneficial for monolithic integration of optical isolator with laser diode. The non-reciprocal loss was experimentally observed in Ga1-xAlxAs waveguide covered by Co for the first time. INTRODUCTION
The optical isolator is an essential component of optical communication systems. It protects laser diodes and optical amplifiers from unwanted reflections. Several types of the waveguide optical isolators were successfully demonstrated using magnetic garnet films grown on oxide substrates [1]-[5]. Because most active optical elements (such as laser diodes, optical amplifiers, modulators, and optical gates) are produced on GaAs or InP substrates, it is desirable to integrate monolithically all optical components on these types of substrates. However, integration of the isolator is a difficult task. Garnet-made isolators have not been monolithically integrated with semiconductor optoelectronic devices, because these oxide crystals can not be grown on semiconductor substrates. Several methods of integrating magneto-optical waveguide devices with semiconductor optoelectronics devices have been proposed. A direct bonding of garnet films was proposed onto InP substrate [6] and onto GaAs substrate [7]. Zaets et al. [8,9] experimentally demonstrated that magnetooptic film of a diluted magnetic semiconductor Cd1xMnxTe grown on GaAs substrate can operate as a magneto-optical waveguide. Hammer et al. [10] proposed to use magneto-optical (MO) properties of the ferromagnetic metal. They showed theoretically that a non-reciprocal TE-TM mode converter can be obtained using a semiconductor waveguide covered by a Fe layer. The magnetization direction was considered to be parallel to the light propagation. An optical amplification by the semiconductor waveguide was used to compensate the loss induced by the metal film. The need of simultaneous phase matching and gain matching between TM and TE modes is a main problem for practical realization of this type of isolator. Zaets et al. [11] proposed a similar structure of the ferromagnetic-metal-semiconductorhybrid isolator, except the magnetization of ferromagnetic metal was perpendicular to the light propagation direction and lies in the film plane. They showed theoretically that in this case there is a large difference in values of loss/gain for modes propagating in the opposite directions. Thus, the amplifier covered by ferromagnetic
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