Microwave photonic frequency down-conversion with self-interference cancellation and SSBI mitigation

Abstract

In this paper, we proposed a microwave photonic frequency down-conversion scheme with the functions of self-interference cancellation (SIC) and signal–signal beat interference (SSBI) mitigation. The scheme is based on a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator. One of the dual-parallel Mach–Zehnder modulator (DP-MZM) which is located in the upper part of the DP-QPSK modulator is used to achieve SIC by properly biasing the modulator. A local oscillator signal is loaded on the other DP-MZM which is located in the lower part of the DP-QPSK modulator. After photoelectric conversion of the combined optical signal by a photo-detector (PD), the signal of interest (SOI) is down-converted to an intermediate frequency (IF) signal. The SSBI is mitigated by Kramers–Kronig (KK) detection to achieve lower IF down-conversion. Experimental results show that the SIC for a single-tone interference signal is around 53 dB, and for an interference signal with a bandwidth of 100 MHz, the SIC achieved at least 29 dB. A simulation verifies the effect which the least mean square (LMS) algorithm mitigated on the influence of multipath After SIC, we used KK algorithm to reduce error vector magnitude (EVM) of the down-converted 16-QAM signal from 17.54% to 9.07%, which indicates a remarkable SSBI mitigation effect.