Phase-sensitive QPSK channel phase quantization by amplifying the fourth-harmonic idler using counter-propagating Brillouin amplification

We experimentally demonstrate all-optical phase-sensitive quantization of a 10-20 Gbaud quadrature phase-shift keying (QPSK) signal's phase without an active phase-locked loop (PLL) by utilizing Brillouin amplification (BA) to amplify the fourth-harmonic idler without path separation, allowing the pump, signal, third-harmonic idler and amplified fourth-harmonic idler to remain synchronized in the phase. We observe up to 65% reduction in phase noise and 4.6 dB gain at a bit-error rate (BER) of 10−4 over 36 min of continues operation.