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The CMOS industry has been expecting silicon photonics to provide photonic and electro-photonic integrated circuits based on the CMOS processes and infrastructures for scalability of incumbent technology evolutions and creation of novel technologies. However, the compatibility with the legacy CMOS has been compromised with the development convenience of early silicon photonics in that the specialty silicon-on-insulator substrates have been widely used as integration platforms. Since this specialty substrate may hinder the photonics integration with legacy volume products later, a legacy-friendly integration platform with a generic bulk-silicon substrate has been developed for better compatibility. This paper overviews the bulk-silicon photonics platform born for DRAM integration, upgraded with III/V-on-bulk-Si lasers, and transplanted to LiDAR applications requiring the virtuous cycle of cost and volume. The photonics integration with DRAM was to resolve the speed-capacity tradeoff in the DRAM interconnects, and technical feasibility as well as lessons learned from the integration attempt are reviewed. The bulk-silicon device performance approaches that of silicon-oninsulator devices with the thermal advantage of ~40-% lower thermal impedance and the optical disadvantage of ~0.4-dB/mm higher waveguide loss. In the LiDAR applications, detection performance up to ~20 m at 20 fps by a single-chip scanner integrating tunable laser, semiconductor optical amplifiers, and optical phased array are presented with future outlooks.

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For the first time, we demonstrate 40-m range detection and 3D depth scan up to 20 m using a silicon-photonic optical phased array with integrated amplifiers, promising a highperformance solid-state light-detection and ranging (LiDAR) system.

The optical phased array has been developed to realize solid-state optical beam steering following the advent of silicon photonics. Thus far, its feasibility has lacked either steering quality or optical efficiency, and its optimal design still remains unknown. Herein, we propose a scalable and wavelength-independent phased array design methodology that achieves steering quality and optical efficiency. This novel design methodology is based on a special aperiodicity from number theory of a complete residue system that is fundamentally suited for phasor cancellation for the desired array sparsity. A specific design derived based on this methodology was implemented in silicon with 128 phase-controlled antennas in the O band, and it was experimentally verified in a two-dimensional steering demonstration that featured a record-high beam-forming efficiency (>30%) and a high-grating-lobe suppression (>10 dB) over a field-of-view of 40 ⅹ 7.2°. This optical efficiency improved by at least 250% compared with prior art.

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