A dual-polarization coherent communication system with simplified optical receiver for UDWDM-PON architecture

A dual-polarization coherent heterodyne optical communication system using a simplified and low-cost demodulation scheme, for high-capacity UDWDM-PON access networks, is proposed and demonstrated. In this scheme, the signal light and reference light occupying each of the polarization modes are emitted simultaneously from the transmitter. The random phase fluctuations between the signal light and reference light are obviated completely by means of the application of the phase-correlated orthogonal lights. When the signal light in the each polarization mode is modulated with M-amplitude-shift keying (M-ASK) or M²-quadrature amplitude modulation (M²-QAM), the phase-stable intermediate frequency (IF) signal with M-ASK or M²-QAM modulation in the corresponding polarization mode is available for conversion in the electrical domain by beating the modulated signal light with the un-modulated reference light. A new IF signal with M² or M⁴-QAM can be synthesized by the IF signals in both modes as long as the power ratio and time delay between the two-modes optical signals are set at the proper values. This is achieved without using polarization demultiplexing and complicated algorithms and the synthesized IF signal can be received and demodulated directly. A proof-of-concept transmission link with dual-polarization 2-ASK is demonstrated. The experimental results are consistent with theoretical predictions.