Hybrid III-V-on-Silicon Microring Lasers
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Hybrid III-V-on-Silicon Microring Lasers 1
Di Liang , Géza Kurczveil1, Marco Fiorentino1, Sudharsanan Srinivasan2, David A. Fattal, Zhihong Huang1, John E. Bowers2 and Raymond G. Beausoleil1 1 Intelligent Infrastructure Lab, Hewlett-Packard Laboratories Palo Alto, CA 94304, U.S.A. 2 Department of Electrical and Computer Engineering, University of California Santa Barbara, CA 93106, U.S.A. ABSTRACT Hybrid silicon laser is a promising solution to enable high-performance light source on large-scale, silicon-based photonic integrated circuits (PICs). As a compact laser cavity design, hybrid microring lasers are attractive for their intrinsic advantages of small footprint, low power consumption and flexibility in wavelength division multiplexing (WDM), etc. Here we review recent progress in unidirectional microring lasers and device thermal management. Unidirectional emission is achieved by integrating a passive reflector that feeds laser emission back into laser cavity to introduce extra unidirectional gain. Up to 4X of device heating reduction is simulated by adding a metal thermal shunt to the laser to “short” heat to the silicon substrate through buried oxide layer (BOX) in the silicon-on-insulator (SOI) substrate. Obvious device heating reduction is also observed in experiment. INTRODUCTION When faced with bandwidth, power, and signal integrity issues on conventional metal interconnects in silicon microelectronics, industry has committed to adopt high-capacity fiberoptic technology to build high-performance optical interconnect systems. Recently developed hybrid silicon platform has emerged as one of the most promising device platform for practical applications [1]. Among a variety of demonstrated hybrid silicon lasers, microring lasers were designed for their intrinsic advantages of small footprint, low power consumption and flexibility in wavelength division multiplexing (WDM), etc. Inset in Fig. 1 shows the schematic of a hybrid Si microring laser where III-V epitaxial layers are transferred to the (SOI) substrate to provide optical gain. A Si bus waveguide is used to extract a portion of optical power from the hybrid cavity [2]. The fabrication starts from transferring the thin InP-based III-V laser epitaxial layers (O=1.515 Pm) onto the SOI by a low-temperature O2-assisted wafer bonding process. Upon blank depositing p-type metal contact and dielectric mask layer on the p-InGaAs layer, a self-aligned process is used to transfer microring pattern through p-type metal, III-V and all the way to silicon layer. Upon passivation the etched sidewall, another photolithography and similar but timed dry etching process is used to form the microring resonator mesa and expose the n-InP contact layer inside. Then n-type contact metal is placed inside the microring resonator, followed by probe-pad metal pad deposition. Detailed fabrication process and epitaxial layer structure can be referred to [2]. Directional bistability, the ability of a laser to operate either in the clock-wise (CW) or counter-clock-wise (CCW) mode due
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