Quantum-dot semiconductor optical amplifier for filter-assisted 80-Gb/s wavelength conversion

Filter assisted all-optical wavelength conversion using a quantum dot (QD) based semiconductor optical amplifier (SOA) is presented. Cross-gain modulation and cross-phase modulation were both used to shift the wavelength of 40-Gb/s and 80-Gb/s return-to-zero on-off keying data signals at 1.3 μm by 10 nm. The ultra-fast gain recovery of the QD´s enables open eyes of the wavelength converted signal with an inverted bit-logic. The slow phase recovery of the carrier reservoir of the QD´s, however, leads to phase patterning which becomes evident after filtering of the converted signal with a delay interferometer, whose free spectral range is set to the bit rate. The phase patterning was mitigated by adjusting the delay interferometer to a large free spectral range. Moreover, the delay interferometer reinverted the converted signal and significantly enhanced the extinction ratio. Using such a wavelength converter scheme error-free (bit-error ratio <; 10^-9) performance was achieved for 40 Gb/s, as well as for the first time with QD SOAs at 80 Gb/s.