Same-Wavelength Bidirectional Coherent Fiber Communication Scheme With OSNR Improved by Raman Amplifiers

We have theoretically deduced the condition where the signal-to-Rayleigh scattering noise (RSN) ratio can be optimally improved in the same-wavelength bidirectional (SWB) fiber communication systems, based on which an integral research about the feasibility of the SWB coherent fiber communication scheme and the benefits compared with the unidirectional system have been carried out. The theoretical deduction shows that the lossless transmission has a best effect on reducing the interference of the RSN on the signal, which has been verified by experiments in terms of OSNR. Based on the theory, systematic experiments have been carried out, during which the distributed Raman amplifiers (DRAs) were utilized to construct the quasi-lossless transmission to improve the OSNR. The results show that with the assistance of DRAs, an extra 90% spectral efficiency (SE) can be obtained over a 75 km fiber and an 80% SE gain should be attained over a 100 km fiber by the same-wavelength bidirectional scheme over the unidirectional system.