Characterization of Phase Shift in Modified Uni-Traveling-Carrier Photodiode

We report the MUTC-PD (modified uni-travelling photodiode)'s phase change for a variation of bias voltage and photocurrent. The photodiode's delay time is calculated by the measured results. Both the simulation and measured results indicate that the extreme point of photodiode's phase is generated by the peak electron velocity. Specifically, the phase change remains constant with increasing photocurrent at two situations: one is when the electron velocity achieves maximum point, the other is when the electron velocity saturates. When the phase change is constant, the slope of phase change versus photocurrent is zero, thus the amplitude-to-phase noise (AM-to-PM) coefficient is null. In more common scenarios, the phase change is proved to depend on transit time and impedance changes with opposite trends, with impedance dominating.