Power Equalization for SOA-Based Dual-Loop Optical Buffer by Optical Control Pulse Optimization

In this paper, a theoretical study and experimental demonstration are applied to achieve power equalization for semiconductor optical amplifier (SOA)-based dual-loop optical buffers (DLOBs). It is found that, due to the gain saturation and limited linewidth-enhancement factor of the SOA, the peak power of a packet pulse with an optically controlled delay of 9.9 $\mu{\hbox {s}}$ is 4.83 dB lower than that of a packet pulse without storage. In order to eliminate the 4.83-dB output power fluctuation of the DLOB, a simple power-equalization method based on the optimization of an optical control pulse is proposed. By injecting a negative optical control pulse, the output power fluctuation of a packet pulse can be effectively reduced to zero. We have also investigated the peak power level of the optical control pulse required to fulfill the buffer function. It is found that the SOA with larger linewidth-enhancement factor and larger small-signal gain should be used to reduce the peak power of the optical control pulse. It is also theoretically found that, due to the negative optical-control pulse injection, the packet signal with Gaussian profile has some distortion after storage. However, the distortion effect is mitigated when the shape of the input pulse is more similar to the square profile. Finally, the proposed method for achieving power equalization in an SOA-based optical buffer has been justified by carrying out a 2.5-Gb/s 2$\,\times\,$2 exchange-bypass optical switch experiment. We believe that this power-equalization method can be also applied to other SOA cross-phase modulation-based applications.