High-Efficiency On-Chip Optical Phase Conjugation Using a Single Ultralow-Loss Silicon Photonic Waveguide

Optical phase conjugation (OPC) is a pivotal all-optical technique aimed at enhancing the received signal quality by compensating for nonlinear distortions. Integrating the OPC into a CMOS-compatible, highly nonlinear silicon photonic chip holds promise for developing fully integrated transceivers with a compact footprint, low loss, and minimal power consumption. Despite its potential, silicon-based OPC demonstrations have been limited, primarily due to challenges, such as inefficient conjugation and significant losses. In this work, we demonstrate an effective OPC technique utilizing a single passive silicon photonic waveguide spiral. This silicon photonic waveguide is meticulously designed with an optimal cross-section to achieve an ultralow loss and high conversion efficiency. The silicon photonic waveguide spiral was fabricated via standard multiproject-wafer processes, and the measured result shows an ultralow loss of 0.25 dB/cm and a high conversion efficiency of −5 dB, marking the highest conversion efficiency reported for passive silicon photonic waveguides to date. The experimentally demonstrated OPC significantly enhances idler generation, resulting in a 3-dB improvement in launched signal power within a 160 Gbit/s 16-QAM transmission system without the need for dispersion compensation for over an 80-km transmission distance.