Fig. 2: Concept of the proposed residual carrier modulation (RCM) scheme.
From: Overcoming laser phase noise for low-cost coherent optical communication
a The architecture of low-cost standard coherent transceivers using distributed feedback (DFB) laser at the transmitter and receiver. IQ Mod. in-phase/quadrature modulator, SSMF standard single-mode fiber, LO local oscillator, ICR integrated coherent receiver. The comparison of b conventional time-domain pilot (TP) and c the proposed RCM enabled carrier phase recovery (CPR). The constellation diagrams and optical spectra at the transmitter, the received electrical spectra, and constellation diagrams after phase recovery are shown. The direct current (DC) bias of modulators is plotted on the left of the transmitter spectra. Freq. frequency, Tx transmitter, Rx receiver. d The digital signal processing procedure for the residual carrier modulation to recover the phase. Δf is the estimated frequency offset value. \({\left\{\cdot \right\}}^{*}\) denotes the complex conjugate operation. FOE frequency offset estimation, LPF low-pass filter. e The frame structure of the time-domain pilot-based CPR. f The principle of frequency-domain pilot tone-based CPR.
