Fig. 3: Residual carrier modulation-enabled terabit coherent transmission system with high-order modulation formats.
From: Overcoming laser phase noise for low-cost coherent optical communication
a The experimental setup of 16-channel wavelength-division multiplexed (WDM) probabilistic-shaped 256-ary quadrature amplitude-modulation (PS-256-QAM) signals. CUT channel under test, ECL external cavity laser, DFB distributed feedback laser, CH channel, PM-OC polarization-maintaining optical coupler, SP IQ Mod. single-polarization in-phase/quadrature modulator, PBC polarization beam combiner, EA electrical amplifier, PDM-E polarization-division-multiplexing emulator, EDFA erbium-doped fiber amplifier, SSMF standard single-mode fiber, WSS wavelength-selective switch, OBPF optical band-pass filter, LO local oscillator, BPD balanced photodetector, RTO real-time oscilloscope. b The measured optical spectra of the channel under test with or without the residual carrier. w/ with, w/o without. c The received electrical spectrum after frequency offset removal.
