Proper Dispersion Tailoring in Semiconductors as Prerequisite for Soliton Formation

Bright solitons to exist in materials with a focusing nonlinearity require an anomalous dispersion (GVD < 0). This condition can be met in fused silica fibers beyond the zero-dispersion wavelength. Unfortunately, semiconductors that are fairly attractive for all-optical elements because of their large off-resonant nonlinearities (below half the band gap) exhibit a huge normal GVD (D≈1000ps2/km) thus prohibiting the formation of bright solitons. Hence, there is a great deal of interest to identify smart device concepts that allow for the overcompensation of the wrong material dispersion. Such concepts could be used to avoid the experimentally observed pulse break up in nonlinear AlGaAs directional couplers by using temporal solitons [1]. Moreover, spatio-temporal objects (light bullets) [2] could be studied because the required interplay of diffraction, anomalous dispersion and focusing nonlinearity would occur in properly designed planar waveguide structures. Because the device length of semiconductor waveguides is limited to about 2" the anomalous dispersion should exceed some thousands of ps2/km for pulse lengths of some hundred fs.