Abstract

The benefit of Brillouin amplification for optical carrier recovery from pilot tones is evaluated in application to coherent signal detection without a conventional local oscillator (LO) laser. The focus being on the narrow gain bandwidth suppressing broadband spectral noise power relative to the pilot tone. Calculations indicate its use at the receiver with realistic 30 dB gain and 30 MHz gain bandwidth permit lowering the minimum pilot tone to signal power ratio (PSR) for low distortion signal demodulation by up to ≈24 dB in the case of a 10 GHz wide signal channel, and even larger for broader channels. The ultimate limit being its ratio to the narrowness of the Brillouin gain bandwidth. Low noise Brillouin gain is also accounted for from characterization by a coherent receiver and digital signal processing approach for an optical fiber used as the gain medium in experiments. Its use in optical carrier recovery from a 3 channel WDM 48 Gb/s 64-QAM signal with polarization multiplexed pilot tones demonstrates improvement consistent with predictions in reducing the impact of pilot tone noise to near that for a conventional LO. The estimated low PSR limit for a bit error rate below the hard decision FEC limit was extrapolated as ≈−38 dB. This rose to ≈−30 dB with inclusion of 80 km link transmission due to the restricted signal launch power for avoiding nonlinear distortion. The insight highlights the wide-ranging capabilities for enhancing performance in advanced coherent communications.

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