We investigate the performance of a semiconductor optical amplifier (SOA) based Sagnac-interferometer switch in its application as time division demultiplexer. By performing dynamic switching window measurements with a time resolution of about 1 ps, the temporal width and the contrast of the switching windows are investigated for SOA lengths of 500, 1000 and 1500 μm. Operating the switch with a control pulse rate of 10 GHz (corresponding to all-optical demultiplexing to 10 Gb/s) the shortest switching windows, still retaining high contrast, are achieved with short SOAs. By increasing the control pulse rate to 40 GHz, the case of an SOA-based all-optical demultiplexer with a base rate of 40 Gb/s is investigated. Though the switching contrast deteriorates for the 40 GHz control pulse rate, the obtainable contrast is still up to 19 dB. This finding encourages the feasibility of SOA-based interferometric demultiplexers with base rates of 40 Gb/s. In particular, this feature will be crucial to future all-optical demultiplexers as the base rate of electronic signal processing is currently evolving to 40 Gb/s.