High-Speed Waveguide InP/InGaAs UTC-PDs for over 200 Gb/s/λ Optical Transmission

Scaling of artificial intelligence data centers is pushing the aggregate speed of photonic transceivers over 1.6 Tb/s and even 3.2 Tb/s, which in the multi-channel configuration accounts for a 200 Gb/s data transmission speed for each wavelength. Uni-traveling carrier photodetectors have proved high bandwidth performance utilizing ultra-fast carrier transit and ultra-small junction capacitance, while few reports discuss the effect of the coplanar lines on bandwidth. In this work, the parasitic effect of coplanar lines is studied, and a modified structure is designed for an InP-based waveguide uni-traveling carrier photodetector. Simulation results reveal a promotion rather than deterioration effect in PD frequency response from the coplanar lines after optimization, and the circuit analysis predicts a parasitic capacitance decrease over 40 fF, which is larger than the 23 fF junction capacitance itself. The fabricated photodetector verifies a 69% increase in bandwidth up to 120 GHz for the same active area at an external responsivity of 0.476 A/W. The eye-diagrams of 100 GBd and 140 GBd under PAM4 format also indicate huge potential for over 200 Gb/s/λ photodetection.