ULTRAFAST NONLINEARITIES IN SEMICONDUCTOR-LASER AMPLIFIERS

The bound-electronic optical nonlinearities in highly excited semicond uctors (i.e., semiconductor lasers) have been calculated using a two-p arabolic-band model. The nonlinear absorption spectrum is first obtain ed using a dressed-state formalism taking into account the contributio ns from two-photon absorption, electronic Raman, and optical Stark eff ects. The nonlinear refractive index (n(2)) is then found by performin g a Kramers-Kronig transformation on the nonlinear absorption spectrum . It is also shown that the quadratic Stark splitting of the bands lea ds to a shift in the quasi-Fermi levels, which introduces additional a bsorptive and refractive nonlinearities. The sign, magnitude, and the current-density dependence of the calculated nz agree well with some r ecently published experimental results for Al-Ga-As and In-Ga-As-P dio de lasers.