Analysis of an ASIC-based Coherent Polarization-Multiplexed QPSK Receiver and Different Receiver Frontends

In this paper we present the characterization results of an optical coherent quadrature phase shift keying (QPSK) receiver with an application-specific integrated circuit (ASIC) based backend unit. Additionally we investigate the performance of an integrated optical coherent receiver frontend (ICR) and compare it against a fiber-pigtailed 90° optical hybrid. After characterization of the CMOS ASIC, we measure and analyze single polarization QPSK transmission at 2.5 Gbaud with different optical receiver frontend setups. Also we measure the polarization-multiplexed QPSK transmission and discuss the possible reasons for reduced sensitivity compared to the single-polarization transmission.