An all-optical switch is proposed and demonstrated using the nonlinear polarization rotation (NPR) with linear
polarization maintenance arising in a semiconductor optical amplifier (SOA). By introducing optical control pulse into
the SOA, the state of polarization (SOP) of the packet signal can be switched between the vertical linear SOP and the
horizontal linear SOP on the Poicáre sphere (PS). Then a polarization beam splitter (PBS) is used to perform
polarization-to-intensity conversion. Thus the input packet signal can be switched between the two output ports of the
PBS. And an extinction ratio of switching operation larger than 20 dB is obtained.
Semiconductor optical amplifiers (SOAs) as nonlinear devices always work in the gain saturation region. Therefore, the saturation gain is an important parameter of SOAs. However, the existing theoretical gain formula greatly deviates from the experimental measurements. We find experimentally that the effect of the absorption loss on the SOA gain cannot be neglected, especially when the SOA is biased into the saturation region. In this paper, considering the influence of the absorption loss, we propose a modification to the SOA gain formula in common use. We are able to validate the revised formula against the experimental measurements. Thus the theoretical formula after modification can be accurately applied to evaluate the SOA gain in practice.