An improved photonic analog-to-digital conversion scheme using Mach-Zehnder modulators with identical half-wave voltages

An improved photonic analog-to-digital conversion (ADC) scheme using Mach-Zehnder modulators (MZMs) is proposed and demonstrated. In the approach, all the MZMs have the same electrode length, which eliminates the need of MZMs with very low half-wave voltages as in the scheme using MZM array with geometrically-scaled half-wave voltages. An electric circuit is employed to realize linear combinations of the detected signals (including subtraction and addition). By properly biasing the MZMs and setting the thresholding voltages in the comparators, a digital Gray-code output is obtained. The proposed ADC scheme can effectively improve the bit resolution compared with the previous photonic ADCs based on the phase-shifting technique. Theoretical analysis and proof-of-concept experiments are presented to verify the feasibility of the proposed approach.