Over 220 GHz evanescently coupled MUTC-PDs with enhanced responsivity

We present evanescently coupled waveguide modified uni-traveling carrier photodiodes (MUTC-PDs) with ultra-wide bandwidth and high responsivity. What we believe to be a novel epitaxial structure incorporating a multilayer input waveguide is designed to enhance the light absorption efficiency. An optimized passivation scheme, on-chip matching resistors, and high-impedance CPW electrodes are introduced to improve the RC response. The fabricated 4 × 5 µm² PDs achieve a record responsivity of 0.56 A/W and a 3-dB bandwidth over 220 GHz, effectively overcoming the typical trade-off in high-speed PDs. Clear eye opening has been demonstrated for 280 Gb/s 4-level pulse amplitude modulation (PAM4), 330 Gb/s PAM6, and 384 Gb/s PAM8 signals.