Novel Direct-Detection Receiver for Orthogonal Offset-Carrier Assisted PDM System

We propose a direct-detection (DD) receiver, consisted of an optical interleaver, a 90° optical hybrid, and two balanced photodiodes (BPDs), for the use in the orthogonal offset-carrier assisted polarization-division-multiplexed (PDM) system. In this receiver, we first separate the PDM signal and orthogonal offset carriers by using an optical interleaver, and then extract the information on the PDM signal by using a 90° optical hybrid and two BPDs. As a result, the PDM signal in the x- and y-polarization states is demultiplexed into the positive- and negative-frequency components, respectively, after the photodetection. Due to the use of BPDs, there should be no signal-signal beat interference (SSBI) in the received signals. As a result, the proposed receiver does not require the use of any digital signal processing (DSP) technique for demultiplexing the PDM signal or mitigating the SSBI. In addition, the required carrier-to-signal power ratio (CSPR) can be reduced to 0 dB, which, in turn, could increase the transmission capacity of the orthogonal offset-carrier assisted PDM system by ~40%. For a demonstration, we implement the proposed DD receiver and use it for the transmission of the 42-Gbaud 32-quadrature amplitude modulation (QAM) PDM signal assisted with the orthogonal offset carriers over 40 km of the standard single-mode fiber (SSMF).