Fast and on-line link optimization for the long-distance two-way fiber-optic time and frequency transfer

The performance of long-distance two-way fiber-optic time and frequency (T/F) transfer is directly affected by link parameters. In this paper, a fast on-line scheme to maximize the signal-to-noise ratio at the T/F transfer link ends (denoted by SNR_W and SNR_E) is proposed by optimizing the gains of bidirectional Erbium-doped fiber amplifiers (Bi-EDFAs). The dedicatedly defined objective optimization functions, ln(1/SNR_W + 1/SNR_E) for microwave and time transfer, and ln(1/SNR_W) for optical frequency transfer, are proven to be a convex function and enable the computation time to be reduced significantly by employing the fast and mature convex optimization algorithm. The linear equations about the objective optimization function and the fiber parameters required by optimization are constructed, and then the fiber parameters are proposed to be on-line obtained accordingly by measuring the concerned SNR at the link end under different EDFA gain configurations and solving the linear equations. The transmission matrixes for the proposed optimization scheme are further derived, which can simplify the implementation in the long-distance multiple EDFAs links. The simulation shows that the proposed algorithm can obtain the optimal parameters consistent with the reported experimental results, and can reduce the computation time by more than four orders compared with the scanning optimization method for a link with more than 6 Bi-EDFAs.