"On-chip Optical Isolators for Silicon Photonics Applications"

Tetsuya Mizumoto, Professor, Graduate School of Science and Engineering, Tokyo Institute of Technology

March 2nd (Friday), 3:30pm
Engineering Science Building (ESB), Room 2001

An optical isolator allows lightwave to propagate only in a specified direction, and, hence, eliminates undesired optical feedback. Currently, commercially available optical isolators are composed of bulk optics and employ the magneto-optic Faraday effect. On-chip integrated optical isolators are to be realized for integrated photonic circuit applications. In this presentation, approaches toward integrating the optical isolator on photonic circuits are addressed focusing on silicon photonics applications.

The most critical issue for integrating optical isolators is to integrate magneto-optic materials, which is important to obtain the nonreciprocal function of optical isolator. A magneto-optic garnet crystal is the best candidate in fiber-optic communication wavelength ranges, since it has a large magneto-optic effect with low optical absorption. Although there are several reports on growth of the rare earth iron garnet on semiconductors, it is still a challenging task to grow a garnet single crystal because of large mismatch in physical parameters. Use of a bonding technology is an alternative approach. We developed the surface activated direct bonding of iron garnet on III-V and silicon, and realized the tight bonding of Ce substituted YIG (Ce:YIG) on silicon at 200-250 oC after oxygen or nitrogen plasma irradiation.

Another issue to be considered is the structure of optical isolators. In an early research of waveguide optical isolators, TE-TM mode conversion was intensively studied. In this configuration, the phase matching between the modes concerned is to be taken, which requires the stringent control of waveguide structures. We have been investigating the isolator based on a magneto-optic phase change. The nonreciprocal transmittance is realized using the magneto-optic phase change in a Mach-Zehnder interferometer (MZI). We demonstrated an isolation of 21 dB at a wavelength of 1559 nm in a silicon MZI isolator, in which Ce:YIG was directly bonded as an upper cladding layer on a silicon rib waveguide. Ghent Univ. also demonstrated an isolation of 25 dB in a BCB bonded MZI isolator.

An alternative approach is to combine the magneto-optic phase change with a ring resonator. UCSB demonstrated a 9 dB isolation in a Si ring resonator based optical isolator with a molecular-bonded Ce:YIG. Also, MIT demonstrated a 19.5 dB isolation in a Si ring resonator on which Ce:YIG/YIG bilayer was deposited by PLD.

About Tetsuya Mizumoto:

Tetsuya Mizumoto received the B.E., M.E., and D.Eng. degrees in Electrical Engineering from Tokyo Institute of Technology, Tokyo, Japan, in 1979, 1981, and 1984, respectively.

Since 1984, he has been a Research Associate at Tokyo Institute of Technology. Currently, he is a Professor with Graduate School of Science and Engineering, Tokyo Institute of Technology. His research has been concerned mainly with waveguide optical devices, especially magneto-optic devices and all-optical switching devices based on the third-order nonlinearity.

Dr. Mizumoto received the Treatise Award in 1994 and the Best Letter Award of Electronics Society Transactions in 2007 from the Institute of Electronics, Information and Communication Engineers (IEICE). He was also awarded an IEEE Photonics Society Distinguished Lecturer Award in 2009. He is a Fellow of IEICE and IEEE, a member of the Japan Society of Applied Physics, and the Magnetic Society of Japan.

Hosted by: Professor John Bowers