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Optically synchronized unidirectional optical amplifiers based coherent optical fiber links
Optics Letters- received 03/27/2024; accepted 04/22/2024; posted 04/24/2024; Doc. ID 524886
- Abstract: We report on the realization of a unidirectional transmission based bidirectional erbium-doped fiber amplifier (UTB-EDFA) for the coherent optical fiber links. By applying an optical phase-locked loop (OPLL) between the two unidirectional EDFAs (Ui-EDFAs) paths, the annoying uncorrelated phase noise between the two paths can be largely suppressed. Promisingly, we can independently optimize the gains of the UTB-EDFAs for bidirectional transmissions, resulting in the higher net gain acquired compared with the conventional single-path bidirectional EDFAs (SPBAs) based ones. We demonstrate that the fractional frequency instability of the UTB-EDFAs based scheme can be decreased by 26.3 % over the most asymmetrical 100 km two-way optical frequency comparison (TWC) system compared with the SPBAs based ones and, more importantly, can acquire higher net gain for unevenly distributed sub-links over ultra-long fiber links, such as 1,000 km, by independently optimizing the gains. This technique paves the way for the applications of the large-scale fiber networks.