Dynamic behavior of optically clocked 4 mm UL-SOA at 40 Gbit/s
Semiconductor optical amplifiers have been applied successfully for optical signal processing, e. g. optical switching, wavelength conversion, demultiplexing, signal regeneration. The principle of operation has been based mainly on cross phase modulation (XPM) and cross gain modulation (XGM), respectively. These effects rely on inter-band recombination resulting in limited modulation bandwidth. To enhance the speed potential of semiconductors, fast nonlinear mechanisms (intra-band effects), e. g. spectral hole burning or carrier heating, should be used. The relative weak efficiency of these nonlinearities can be increased by extending the length of the SOAs. However, pattern effects due to the slow but strong effects discussed before are dominant in this case and seem to hinder their use. In this paper we investigate a novel technique for suppressing the pattern effects in ultra-long SOAs (UL-SOA). The gain dynamic in the UL-SOAs is here stabilised by a sinusoidal optical clock signal which is injected into the device, bit interleaved with a PRBS data signal. We designed and fabricated 4 mm long devices with polarisation insensitive strained bulk active layer and a gain peak at 1565 nm. We demonstrate, that the pattern effects in the UL-SOA are significantly suppressed. The characteristics of the novel scheme are investigated in detail at 40 Gbit/s. Finally, we exploit the ultra-fast nonlinearities in the UL-SOAs for regenerating a 40 Gbit/s data signal in amplitude, time and pulse shape.