Nonlinear refractive index and pattern-effects-free cross-phase modulation in quantum dot semiconductor optical amplifiers

We have developed a theory of the nonlinear refractive index in Quantum Dot (QD) Semiconductor Optical Amplifiers (SOAs) due to Spectral Hole Burning (SHB). Estimates show that this SHB nonlinear refractive index can be of order of 4.10(-16) m(2)/W that is by four orders higher than the nonlinear refractive index in silica, and offers the possibility of an efficient ultrafast Cross-Phase-Modulation (XPM) in QD SOAs. The opportunity of XPM without patterning effects via this refractive index nonlinearity is discussed. The Pattern-Effect-Free (PEF) XPM is possible in QD SOAs at high pumps, when maximal (constant) gain is achieved in SOAs, and the linear and nonlinear refractive indices also become independent of the total carrier density in the QD structure. In whole, use of the ultrafast refractive index nonlinearity in the regime of maximum gain in QD SOAs can lead to the development of a new generation of nonlinear interferometers for ultrafast optical switching.