Ultra-low loss fully-etched grating couplers for perfectly vertical coupling compatible with DUV lithography tools

G. Dabos; N. Pleros; D. Tsiokos

doi:10.1117/12.2211374

14 March 2016 Ultra-low loss fully-etched grating couplers for perfectly vertical coupling compatible with DUV lithography tools

G. Dabos, N. Pleros, D. Tsiokos

Author Affiliations +

Proceedings Volume 9752, Silicon Photonics XI; 975212 (2016) https://doi.org/10.1117/12.2211374
Event: SPIE OPTO, 2016, San Francisco, California, United States

Abstract

Hybrid integration of VCSELs onto silicon-on-insulator (SOI) substrates has emerged as an attractive approach for bridging the gap between cost-effective and energy-efficient directly modulated laser sources and silicon-based PICs by leveraging flip-chip (FC) bonding techniques and silicon grating couplers (GCs). In this context, silicon GCs, should comply with the process requirements imposed by the complimentary-metal-oxide-semiconductor manufacturing tools addressing in parallel the challenges originating from the perfectly vertical incidence. Firstly, fully etched GCs compatible with deep-ultraviolet lithography tools offering high coupling efficiencies are imperatively needed to maintain low fabrication cost. Secondly, GC's tolerance to VCSEL bonding misalignment errors is a prerequisite for practical deployment. Finally, a major challenge originating from the perfectly vertical coupling scheme is the minimization of the direct back-reflection to the VCSEL’s outgoing facet which may destabilize its operation. Motivated from the above challenges, we used numerical simulation tools to design an ultra-low loss, bidirectional VCSEL-to-SOI optical coupling scheme for either TE or TM polarization, based on low-cost fully etched GCs with a Si-layer of 340 nm without employing bottom reflectors or optimizing the buried-oxide layer. Comprehensive 2D Finite-Difference-Time- Domain simulations have been performed. The reported GC layout remains fully compatible with the back-end-of-line (BEOL) stack associated with the 3D integration technology exploiting all the inter-metal-dielectric (IMD) layers of the CMOS fab. Simulation results predicted for the first time in fully etched structures a coupling efficiency of as low as -0.87 dB at 1548 nm and -1.47 dB at 1560 nm with a minimum direct back-reflection of -27.4 dB and -14.2 dB for TE and TM polarization, respectively.

Citation Download Citation

G. Dabos, N. Pleros, and D. Tsiokos "Ultra-low loss fully-etched grating couplers for perfectly vertical coupling compatible with DUV lithography tools", Proc. SPIE 9752, Silicon Photonics XI, 975212 (14 March 2016); https://doi.org/10.1117/12.2211374

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