Low-Threshold Chirality-Enabled Silicon Photonic Diode

Optical nonlinearity offers a promising pathway for advancing passive silicon photonic diodes and enabling precise control of on-chip light flow. However, the realization of nonlinearity-based photonic diodes often requires high-power excitation, a common constraint in conventional nonlinear devices. In this study, a passive silicon photonic diode based on a nonlinear chiral microring resonator is proposed. The chiral property is introduced by perturbing the evanescent field with two nanocylinders, which minimizes the additional loss compared to other approaches for initiating chirality. This method significantly reduces the mode volume without compromising the quality (Q) factor, resulting in the experimental demonstration of a 5-µm radius chiral microring with Q factor ≈68155. Consequently, the proposed photonic diode achieves an exceptionally low threshold power of P_th ≈−7.83 dBm. The diode maintains low-threshold nonreciprocal behavior during thermal tuning, facilitating an extended operational bandwidth. This work provides a practical solution for the large-scale integration of passive photonic diodes within silicon photonic circuits.