Optical phase-locked loop for coherent transmission over 500km using heterodyne detection with fiber lasers

抄録

We have developed an optical phase-locked loop (OPLL) that can operate over 500km. The coherent transmitter is a 1.54µm ¹³C₂H₂ frequency-stabilized CW fiber ring laser with a frequency stability of 2.0 × 10^-11 and a linewidth of 4kHz. To obtain wide band operation with a bandwidth of 1GHz, we fabricated a high-speed fiber laser as a local oscillator. By using these fiber lasers, the OPLL circuit successfully generated an intermediate frequency signal with a phase error variance of 7.9 × 10^-3 rad.