High-power evanescently coupled waveguide MUTC-PDs for low-phase-noise microwave generation

We demonstrate evanescently coupled waveguide modified uni-traveling carrier photodiodes (WG-MUTC-PDs) with high output power. A cliff layer with optimized doping concentration is investigated to achieve the maximized power handling capability while maintaining the desired transit-time bandwidth. A waveguide layer with optimized refractive index enables efficient evanescent coupling into the absorption layer, maximizing the internal responsivity for both TE and TM modes. Optoelectronic collaborative simulation is adopted to study the localized carrier behavior and saturation characteristics of waveguide photodetectors (PDs) under diverse epitaxial structures and illumination conditions, elucidating our proposed structure maintains a high RF output power while ensuring maximum optical-to-electrical external responsivity. The fabricated device achieves a 3-dB bandwidth of 147 GHz, an external responsivity of 0.492 A/W, and a saturated RF power of 3.09 dBm at 100 GHz, effectively overcoming the traditional speed-efficiency-power trade-offs in PDs. The amplitude-to-phase (AM-to-PM) conversion coefficients under distinct frequencies and biases are characterized, maintaining below 1 degree across 1-11 mA photocurrent. Critically, the residual phase noise at 100 GHz for the PDs are evaluated for the first time in a photonic-based microwave generation system.