Control of Intercore Crosstalk Accumulation Over the C+L Band With Spectral Inversion Technique Using PPLN-Based Optical Phase Conjugation

Intercore crosstalk (IXT) is the main factor affecting the signal quality in uncoupled multicore fiber (MCF) transmissions, and its wavelength dependence has a large effect—especially in wide-band transmissions. We propose a technique for optical spectrum inversion to mitigate the wavelength dependence of the IXT and an advanced “bandwidth-partitioned spectral inversion (BPSI)” technique specifically for wider-band transmissions. We analytically found that these techniques are valid for ITU.T G.652.D-compliant step-index MCF and G.657.A1-compliant trench-assisted fiber to suppress the IXT difference to 0.3 dB over 11 THz and found that they also enable suppressing almost independently on a combination of fiber parameters, core radii, relative refractive indexes, and core pitches. We experimentally demonstrated these techniques over a 4-core step-index fiber transmission line by applying periodically poled lithium niobate (PPLN)-based optical phase conjugation for spectral inversion. The difference in the mean value of the IXT over the C+L band was reduced from 8 dB to less than 1 dB by applying BPSI. The signal degradation by IXT among wavelength channels in C+L-band transmission condition with 96-Gbaud PCS-64QAM signals also had less wavelength dependence with BPSI and resulted in decrease of IXT-induced OSNR penalty by up to 1.5 dB in the L-band, allowing the wider-band MCF transmission by mitigating the IXT impact at the longer-wavelength channels.