Mitigation of Nonlinear Effects on WDM QAM Signals Enabled by Optical Phase Conjugation With Efficient Bandwidth Utilization

Abstract

Abstract-We present nonlinear impairment mitigation of wavelength division multiplexed (WDM) signals, through optical phase conjugation (OPC). We conduct our experiments on a 400-km long installed fiber link equipped with erbium-doped fiber amplifiers (EDFAs), with the OPC placed close to the middle of the link. Our OPC configuration realizes efficient reuse of the signal bandwidth, avoiding the loss of half of the spectral band typical of most phase conjugating schemes. We demonstrate the operation of the system using both 16-and 64-quadrature amplitude modulation (QAM) signals and report Q-factor improvements up to 0.5 and 2.5 dB for 16-and 64-QAM, respectively.Index Terms-Fiber nonlinearity, nonlinear noise mitigation, optical fiber communication, optical phase conjugation, wavelength division multiplexing.

Combating Fiber Nonlinearity Using Dual-Order Raman Amplification and OPC

“…Several techniques including digital back propagation (DBP), phase conjugated twin-wave, and mid-link optical phase conjugation (OPC), have been investigated to combat such nonlinear impairments [1][2][3]. OPC has been proven to be a promising all-optical signal processing technique to compensate both linear (mainly dispersive) and nonlinear impairments simultaneously for multiple Wavelength Division Multiplexed (WDM) channels [4][5][6][7]. However, the compensation efficiency in a mid-link OPC system is highly dependent on the symmetry of the signal power profile along the fibre (in reference to the middle of the link), which means that full nonlinearity compensation can only be achieved when the signal power is precisely matched on either side of the midlink OPC [3].…”

448-Gb/s PAM4 Transmission Over 300-km SMF-28 Without Dispersion Compensation Fiber

“…Four erbium-doped fiber amplifiers (EDFAs) compensated for the fiber loss. The second fiber link is a part of the UK's NDFIS dark fiber network [8], which connects London and Reading via two relay stations at Telehouse and Powergate in the UK. The installed fiber link consists of 262-km SMF-28 with an average loss of about 0.26 dB/km and an average dispersion of approximately 16.5 ps/(nm•km).…”

Optical Phase Conjugation in Installed Optical Networks

“…The main features of the OPC module include insensitivity to the polarization of the incoming signal(s) and efficient bandwidth utilization in a single nonlinear medium [2,3]. Polarization insensitivity was enabled by an orthogonally polarized dual-pump four-wave mixing (FWM) configuration.…”

“…As with many all-optical processing systems, OPC-based transmission becomes more economically attractive as the number of WDM channels that are processed in the phase conjugator increases. To date, WDM experiments of up to six polarization multiplexed (PM) channels carrying 64-QAM signals have been demonstrated [3], one recent experiment with a single polarization multiplexed (PM) 256-QAM channel. Both demonstrations used dispersion-managed transmission links [4].…”