Dynamic range and switching speed limitations of an N×N optical packet switch based on low-gain semiconductor optical amplifiers

Two important system performance limitations-dynamic range and switching speed-of an integrated packet switch fabric based on low-gain semiconductor optical amplifiers (SOA´s) have been examined by using cascaded blocks of an SOA model, which includes transient effect, nonlinear pulse distortion effect, and amplified spontaneous emission (ASE) noise. Low-gain SOA´s were used to minimize ASE noise considering that no optical filters can be integrated in an SOA-based switch fabric. The system performance with and without a narrowband optical filter at the receiver were both studied. By assuming fixed-wavelength transmitters and no optical filter can be used at the receiving end owing to the unpredictability of arriving packet wavelengths, our simulation results indicate that the dynamic ranges of 4×4 and 8×8 SOA-based packet switches at 2.5 Gb/s can only be about 3.2 and 0.8 dB, respectively. However, at 155 Mb/s, even without a receiving-end optical filter, the dynamic range of each switch size can be increased by more than 17 dB as compared to the cases of 2.5 Gb/s. Note that the dynamic ranges were estimated under the conditions of a bit error rate (BER) ⩽10^-9 and a pulse distortion ratio ⩽30%. We have also shown that, when an optical filter with a 1 nm bandwidth was used at the receiving end to simulate (1) a circuit-switched condition where the center wavelength of the filter can be adjusted according to the established circuit, or (2) a packet-switched condition where each receiver has a wavelength demultiplexer and a detector array, the dynamic range of 4×4 and 8×8 switches can be increased to 16.3 and 14 dB, respectively, at 2.5 Gb/s