Waveband-Shift-Free Optical Phase Conjugator for Spectrally Efficient Fiber Nonlinearity Mitigation

We discuss a novel broadband, polarization-insensitive, and wavelength-shift-free optical phase conjugator (OPC). In the OPC scheme, the original input signal is inherently suppressed in a polarization-diversity loop setup. This allows for spectrally efficient, wavelength-(band)-shift-free generation of phase-conjugated idlers over a continuous operating band. The idlers are generated using four-wave mixing in nonlinear fibers using out-of-band, orthogonally polarized pump waves. The saturation characteristics of the exploited nonlinear mixing process as well as the crosstalk characteristics of the OPC diversity loop scheme are investigated. The OPC subsystem is finally utilized for fiber nonlinearity mitigation by midlink spectral inversion in 800-km transmission experiments over dispersion-managed fiber spans with lumped amplification by Erbium-doped fiber amplifiers. Q
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-factor improvements of up to 0.7 dB are obtained in transmission of a 300-GHz wide 1.6 Tb/s super channel consisting of eight 200 Gb/s polarization division multiplexed 16-ary quadrature amplitude modulation subchannels.