Brillouin Amplification for Enhanced Coherent Communication Applications

Brillouin amplification and its benefit for coherent communication applications with 64-QAM signals is evaluated. This utilizes the narrow gain bandwidth in the tens of megahertz range to enhance the carrier to noise ratio (CNR) of noisy spectral lines applied to either signal carriers at the transmitter before data modulation or pilot tones at the receiver for coherent detection. This expands on the projected capability of 30 dB gain enabling up to ≈24 dB enhancement of CNR and the same reduction of the minimum tolerable pilot to signal power ratio (PSR) for maintaining the same performance than without in case of 48 Gb/s 64-QAM signals. The limit being the narrowness of the Brillouin gain bandwidth (≈30 MHz). Here, the tolerance to larger Brillouin noise and its avoidance with reduced gain of ≈25 dB permitting wider detuning from optimum of the pump frequency and its state of polarization with reduced power oscillations are shown. Extended analysis of carrier recovery for 48 Gb/s 64-QAM signals also indicate a capable low PSR near ≈−40 dB for a bit error rate below the hard decision FEC threshold. This includes with 80 km link transmission and its induced nonlinear signal distortion. Overall, rather than an impediment, Brillouin amplification shows significant performance benefit for wide ranging conditions.