Limitations on ultrafast optical switching in a semiconductor laser amplifier operating at transparency current

Ultrafast optical switching in a semiconductor laser amplifier (SLA) at tra nsparency current is studied under a strong pump condition. The switch conf iguration is a nonlinear optical loop mirror with a SLA as the nonlinear el ement. We demonstrate optical switching with 2 ps recovery time and 60% non linear transmission at switching energy of 9 pJ. We find that the transpare ncy current is pump power dependent and that the transparency current is di fferent for uniform 7-bit input control pulses at 100 Gb/s. We believe thes e two outcomes are due to significant carrier generation via two photon abs orption (TPA) at high pump intensity. To verify our hypothesis, we modify c oupled propagation equations by including the carrier generation due to the TPA and solve the equations numerically. Good agreement between the experi mental and simulation results is obtained. We conclude that to achieve comp lete pattern-independent 100 Gb/s optical switching using a SLA at transpar ency current, we have to avoid TPA or use the SLA with a transit time short er than the control pulse width. (C) 1999 American Institute of Physics. [S 0021-8979(99)06221-0].