Interferometric Optical Isolator with Si Guiding Layer Operated in Unidirectional Magnetic Field

Abstract

INTRODUCTIONIn optical communication systems, an optical isolator is indispensable in protecting active photonic devices from unwanted reflected light. An optical isolator with a Si guiding layer is a significant device for silicon photonic integrated circuits. In this paper, the authors report on an interferometric optical isolator with a Si guiding layer which can be operated in unidirectional magnetic field.DEVICE STRUCTUREFigure 1 shows an interferometric optical isolator with a Si guiding layer employing a nonreciprocal phase shift [1]. The nonreciprocal phase shift occurs in transverse-magnetic (TM) modes that travel in magneto-optic waveguides in which magnetization is aligned transverse to the light propagation direction in the film plane. The optical isolator employing the nonreciprocal phase shift is attractive because the device utilizes TM modes only so that there is no need for phase matching. The optical isolator includes an optical interferometer that consists of two coupling devices, a nonreciprocal phase shifter and a reciprocal phase shifter. In Fig. 1, one arm in the optical interferometer has a magnetic garnet cladding layer. When the interferometer has distinct layer structures, the optical isolator can be operated in a unidirectional magnetic field. The optical isolator employing the nonreciprocal phase shift was designed at 1.55 μm. The nonreciprocal phase shifts in the magneto-optic waveguides with a magnetic-garnet/Si/SiO2 structure were calculated. The multimode interference (MMI) coupler and the reciprocal phase shifter were also designed. As a preliminary experiment, deposition of the magnetic garnet crystals were investigated on various substrates.ACKNOWLEDGMENTThis work was partially supported by the SIT Research Center for Green Innovation.REFERENCES1. H. Yokoi, T. Mizumoto and Y. Shoji, Appl. Opt., 42, 6605 (2003). Figure 1