Characterization of Phase Shift in UTC Photodiode and MUTC Photodiode

The characterizations of phase shift for UTC-PD and MUTC-PD are studied with a variation of light intensity and bias voltage. Both the thinner depleted region and higher operation bias voltage can bring a higher electric field in depleted layer, thereby counteract the impact of self-induced electric field on electron velocity. Thus, we conclude that thickness of depleted region and operation bias voltage can affect the stability of PD's phase. It is also demonstrated that the extreme values of electron transit-time correspond to extreme points of phase change and AM-to-PM null points through calculation. Besides, the stability of electron velocity is proved to determine the stability of phase shift with a variation of optical power.