Quantum-dot semiconductor optical amplifiers for high-bit-rate signal processing up to 160 Gb s^-1 and a new scheme of 3R regenerators

This paper presents a theory and simulation of quantum-dot semiconductor optical amplifiers (SOAs) for high-bit-rate optical signal processing. The theory includes spatial isolation of quantum dots, carrier relaxation and excitation among the discrete energy states and the wetting layer, grouping of dots by their optical resonant frequency under the inhomogeneous broadening, and the homogeneous broadening of the single-dot gain, which are all essential to the amplifier performance. We show that high-speed gain saturation occurs due to spectral hole burning under the optical pulse trains up to at least 160 Gb s^-1 with negligible pattern effect, and that the self-assembled InGaAs/GaAs quantum-dot SOAs have about two to three orders faster response speed than bulk InGaAsP SOAs, with one order larger gain saturation for the 160 Gb s^-1 signals. We also show that switching functions can be realized by the cross gain modulation between the two wavelength channels when the channel separation is within the homogeneous broadening. These results indicate great potential of quantum-dot SOAs for all-optical high-speed switches. As one of their possible applications, we propose a new signal-processing scheme of a `quantum-dot 3R regenerator'.