Overcoming the Rayleigh Backscattering Limit of Same-Wavelength Bidirectional Transmission Using Phase-Sensitive Amplification

Due to the continuous growth of traffic demand, the capacity of current fiber optical networks offered by the conventional telecom bands will soon be exhausted. Bidirectional transmission, in which signals of the same wavelength are transmitted in opposite directions of a single fiber, is an attractive option for increasing the capacity of installed fiber links. However, the transmission distance and capacity of same-wavelength bidirectional links are limited by Rayleigh backscattering. Here, we present a method to improve the performance of same-wavelength bidirectional transmission by alleviating the Rayleigh backscattering induced signal distortion using phase-sensitive amplification (PSA). Relying on the phase-sensitive gain property, the optical signal-to-backscattering ratio, which dominates the received signal-to-noise ratio of the bidirectional transmission link, can be improved by at least 3 dB. Using this approach, we successfully demonstrate wavelength-division-multiplexed 16QAM same-wavelength bidirectional transmission over a 102-km G.652.D standard single-mode fiber. The proposed solution paves the way for bidirectional transmission beyond backscattering-limited capacity, enabling capacity expansion without the need for new fibers or redesigned transceivers outside of conventional bands. In addition, the concept of using the phase-dependent nature of PSA to mitigate the negative impact of Rayleigh backscattering is of interest for other physical systems that are negatively affected by backscattering.