Small-signal modulation response and −3dB bandwidth of reflective semiconductor optical amplifier based fiber cavity laser

In this paper we propose a small-signal model of a reflective semiconductor optical amplifier (RSOA) based fiber cavity laser (FCL), which can be used for determining the small-signal modulation response and the corresponding −3dB bandwidth. The model is encapsulated in a boundary value problem (BVP), which, through the boundary condition, accounts for the fiber cavity transfer function. Starting from the numerical solution of the BVP, we investigate the modulation response and the −3dB bandwidth of an RSOA-FCL. We show that, due to the round-trip group delay, the RSOA-FCL’s modulation response exhibits oscillatory behavior. The bandwidth of an RSOA-FCL is analyzed with respect to the RSOA’s bias current density and active region length, the distribution fiber length, and the spectral width of an optical band-pass filter. We find that, in case of significant fiber dispersion, the bandwidth of FCL is limited by the lower of the two bandwidths — RSOA’s or fiber’s, usually the latter one. In case of small or negligible fiber dispersion, the bandwidth of FCL can be improved by increasing the RSOA’s bias current or fiber length and/or selecting the optimal RSOA active region length, and is limited by the RSOA’s performance.