Ultra-compact high-Q silicon microring resonator for terahertz microwave photonics.

Microring resonators (MRRs) are key building blocks for conventional integrated microwave photonic signal-processing circuits due to their compact footprint and tailorable resonant response. However, when the operating frequency further extends into the terahertz regime, simultaneously achieving a high quality (Q) factor and a terahertz-scale FSR remains highly challenging, primarily because ultra-small bending radii generally introduce excessive optical loss. In this Letter, we report an ultra-compact silicon MRR based on a multimode-interference-assisted generalized Euler-circular (GEC) bend, which alleviates the long-standing Q-FSR trade-off by enabling low-loss operation in ultra-compact microrings. Fabricated in a standard silicon photonics foundry, the device exhibits an intrinsic Q of 3×106 and an FSR of 425 GHz (0.4 THz). To the best of our knowledge, this result represents the highest reported Q × FSR product of 1275 for a compact silicon MRR. Moreover, with an optical resonance linewidth of around 150 MHz, ultrawide consistent photonic filtering operation is validated up to 110 GHz. These results provide a compact and high-performance platform for high-resolution signal processing in THz communication systems.