Abstract

Ultrafast nonlinear refraction (characterised by the coefficientn₂=Δ/l) in semiconductor waveguides at the half-band-gap has been utilised for all-optical switching¹and spatial solitons.²The polarisation dependence ofn₂is important to the following issues: (1) choosing the device and polarisation orientation which optimises |n₂| or the all-optical switching figure-of-merit, (2) selecting or avoiding nonlinear coupling between orthogonal polarisations — this can give rise to nonlinear optical activity and (3) assessing the relative magnitudes of self-phase-modulation and perpendicular cross-phase-modulation for the case of two orthogonally polarised beams. For materials of cubic symmetry belonging to the classes 432, m3m or$\overline{4}3$m (e.g. zinc-blende semiconductors), a total of three independent parameters (strength, induced birefringence and anisotropy) are required for a complete description of the polarisation dependence for degenerate (single wavelength) nonlinear refraction. The dispersion of these parameters is calculated for GaAs³and is consistent with self- and cross-phase-modulation measurements at the half-gap in an Al_0.18Ga_0.82As waveguide.⁴In particular a significant anisotropy inn₂is predicted and observed in semiconductors in the vicinity of the half-bandgap.

© 1996 IEEE