Optical Format Conversion of Phase-to-Intensity-Modulated Signals Based on Delay Line Interferometer and Phase-Sensitive Amplification

An all-optical format conversion (AOFC) scheme from differential quadrature phase shift keying (DQPSK) signals to 4-ary pulse amplitude modulation (PAM4) signals is proposed and simulated based on delay line interferometer (DLI) and partial phase-sensitive amplification (PSA) in this paper. The DLI with 1-symbol time delay is used to convert the DQPSK signal to the probability shaping 9-ary quadrature amplitude modulation (PS-9QAM) signal. The partial PSA based on degenerate four-wave mixing (FWM) is deployed to convert the PS-9QAM signal into one PAM4 signal by compressing the constellations of the PS-9QAM signal. Error-vector-magnitude (EVM) and bit-error-rate (BER) of the optical signals before and after AOFC are measured to evaluate the scheme performance. The constellations and eye diagrams of the optical signals before and after AOFC also prove that the proposed scheme is effective. The proposed AOFC scheme can be utilized to enable an all-optical gateway with data format conversion capacity to bridge the long-haul and short-reach optical networks.