Fig. 5: Simulation and experimental results of the single-channel probabilistic-shaped 256-ary quadrature amplitude-modulation (PS-256-QAM) signal under different transceiver laser setup.
From: Overcoming laser phase noise for low-cost coherent optical communication
a The optical signal-to-noise ratio (OSNR) penalty for different linewidth sum and symbol period product Δf × Ts with conventional time-domain pilot (TP) enabled phase recovery and residual carrier modulation (RCM) under simulation. b The measured normalized generalized mutual information (NGMI) versus the OSNR for different signal (Tx) and local oscillator (Rx) lasers using RCM in the back-to-back experiment. Tx, transmitter; Rx, receiver. c The measured generalized mutual information (GMI) for the different pilot ratios of the TP-based phase recovery with 100 kHz, 1 MHz, and 3 MHz linewidth signal lasers in the back-to-back experiment at an OSNR of 41 dB. The results of RCM are also plotted for comparison. The gross rate and net rate respectively denote the GMI that includes pilot overhead and the GMI that excludes pilot overhead. w, with. d The measured GMI for different signal and local oscillator lasers with RCM at a transmitted OSNR of 40 dB in the 80 km transmission experiment. e The recovered PS-256-QAM constellation for 100 kHz and 3 MHz signal laser with 100 kHz local oscillator using RCM scheme or TP-based phase recovery at an OSNR of 41 dB. LW linewidth, 4D 4-dimensional. f The measured NGMI using RCM or radio-frequency (RF) pilot tone for phase recovery under different receiver-side pilot tone to signal power ratio (PTSPR) with 3 MHz signal laser and 100 kHz local oscillator laser. The receiver-side PTSPR denotes the measured power ratio between the pilot tone and signal in the electrical domain.
