Progress in silicon-based reconfigurable and programmable all-optical signal processing chips

Taking the advantage of ultrafast optical linear and nonlinear effects, all-optical signal processing (AOSP) enables manipulation, regeneration, and computing of information directly in optical domain without resorting to electronics. As a promising photonic integration platform, silicon-on-insulator (SOI) has the advantage of complementary metal oxide semiconductor (CMOS) compatibility, low-loss, compact size as well as large optical nonlinearities. In this paper, we review the recent progress in the project granted to develop silicon-based reconfigurable AOSP chips, which aims to combine the merits of AOSP and silicon photonics to solve the unsustainable cost and energy challenges in future communication and big data applications. Three key challenges are identified in this project: (1) how to finely manipulate and reconfigure optical fields, (2) how to achieve ultra-low loss integrated silicon waveguides and significant enhancement of nonlinear effects, (3) how to mitigate crosstalk between optical, electrical and thermal components. By focusing on these key issues, the following major achievements are realized during the project. First, ultra-low loss silicon-based waveguides as well as ultra-high quality microresonators are developed by advancing key fabrication technologies as well as device structures. Integrated photonic filters with bandwidth and free spectral range reconfigurable in a wide range were realized to finely manipulate and select input light fields with a high degree of freedom. Second, several mechanisms and new designs that aim at nonlinear enhancement have been proposed, including optical ridge waveguides with reverse biased PIN junction, slot waveguides, multimode waveguides and parity-time symmetry coupled microresonators. Advanced AOSP operations are verified with these novel designs. Logical computations at 100 Gbit/s were demonstrated with self-developed, monolithic integrated programmable optical logic array. High-dimensional multi-value logic operations based on the four-wave mixing effect are realized. Multi-channel all-optical amplitude and phase regeneration technology is developed, and a multi-channel, multi-format, reconfigurable all-optical regeneration chip is realized. Expanding regeneration capacity via spatial dimension is also verified. Third, the crosstalk from optical as well as thermal coupling due to high-density integration are mitigated by developing novel optical designs and advanced packaging technologies, enabling high-density, small size, multi-channel and multi-functional operation with low power consumption. Finally, four programmable AOSP chips are developed, i.e., programmable photonic filter chip, programmable photonic logic operation chip, multi-dimensional all-optical regeneration chip, and multi-channel and multi-functional AOSP chip with packaging. The major achievements developed in this project pave the way toward ultra-low loss, high-speed, high-efficient, high-density information processing in future classical and non-classical communication and computing applications.