Two-photon absorption-induced self-phase modulation in GaAs–AlGaAs waveguides for surface-emitted second-harmonic generation

Performance-limiting asymmetric distortion is observed in the spectra of fundamental pulses transmitted through $\mathrm{GaAs}–{\mathrm{Al}}_{0.9}{\mathrm{Ga}}_{0.1}\mathrm{As}$ multilayer waveguides designed for surface-emitted second-harmonic generation. This behavior is attributed to refractive-index changes resulting from the accumulation of free carriers created by two-photon absorption in the GaAs layers. Numerical simulations of the intensity-dependent spectra by use of the separately measured two-photon absorption coefficient are shown to be in good agreement with the observed spectra.