Simple carrier-phase estimator for high-speed RSOA-based coherent WDM PON.

It has been recently reported that reflective semiconductor optical amplifiers (RSOAs) can be used as phase modulators for the cost-effective implementation of the high-speed wavelength-division-multiplexed passive optical networks (WDM PONs). For the detection of the phase-shift-keying (PSK) signal generated by using an RSOA, we should be able to estimate its carrier phase accurately at the digital coherent receiver. However, when the baud rate of this PSK signal is set to be much higher than the RSOA's modulation bandwidth, the conventional M-th power algorithm cannot estimate its carrier phase accurately. To solve this problem, we develop a simple carrier-phase estimation technique for the high-speed (>10 Gb/s) PSK signals generated by using bandwidth-limited RSOAs. This technique estimates the carrier phase of the PSK signal by measuring the angular direction of the opening occurred in the trajectory of the phasor diagram. By using the proposed technique, we demonstrate the upstream transmission of the 25.78-Gb/s quadrature phase-shift-keying (QPSK) signal generated by using an RSOA (3-dB bandwidth: 3.2 GHz) in a 60-km reach coherent WDM PON.