Raman/EDFA hybrid bidirectional amplifier for fiber-optic time and frequency synchronization

Herein, we verify that a Raman/EDFA hybrid amplifier can improve the stability of fiber-optic time and frequency synchronization systems compared to the Er -doped fiber amplifier (EDFA), owing to its higher gain and lower noise figure (NF) performance. We studied the variation law of Raman gain efficiency for a fiber Raman amplifier (FRA) as a function of pump power and input signal power, designed a bidirectional Raman/EDFA hybrid amplifier, and proved that equivalent NF below 0 dB can be obtained. Finally, hybrid amplifiers were compared to EDFAs in a free-running frequency synchronization system. The transfer stabilities reached 1.9678 × 10 /1 s and 2.0248 × 10 /1 s when FRA + EDFA and EDFA + FRA configurations were used, respectively, both exhibiting better performance than the stability of 3.0905 × 10 /1 s obtained by EDFA.