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Materials 2012, 5(5), 985-1004;

Direct Wafer Bonding and Its Application to Waveguide Optical Isolators

Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8552, Japan
Author to whom correspondence should be addressed.
Current address: Network Photonics Research Center, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki, 305-8568, Japan.
Received: 31 March 2012 / Revised: 18 May 2012 / Accepted: 21 May 2012 / Published: 24 May 2012
(This article belongs to the Special Issue Photonic Materials and Applications)
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This paper reviews the direct bonding technique focusing on the waveguide optical isolator application. A surface activated direct bonding technique is a powerful tool to realize a tight contact between dissimilar materials. This technique has the potential advantage that dissimilar materials are bonded at low temperature, which enables one to avoid the issue associated with the difference in thermal expansion. Using this technique, a magneto-optic garnet is successfully bonded on silicon, III-V compound semiconductors and LiNbO3. As an application of this technique, waveguide optical isolators are investigated including an interferometric waveguide optical isolator and a semileaky waveguide optical isolator. The interferometric waveguide optical isolator that uses nonreciprocal phase shift is applicable to a variety of waveguide platforms. The low refractive index of buried oxide layer in a silicon-on-insulator (SOI) waveguide enhances the magneto-optic phase shift, which contributes to the size reduction of the isolator. A semileaky waveguide optical isolator has the advantage of large fabrication-tolerance as well as a wide operation wavelength range. View Full-Text
Keywords: waveguide device; magneto-optics; direct wafer bonding; optical isolator waveguide device; magneto-optics; direct wafer bonding; optical isolator

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Mizumoto, T.; Shoji, Y.; Takei, R. Direct Wafer Bonding and Its Application to Waveguide Optical Isolators. Materials 2012, 5, 985-1004.

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