Abstract

Optical limiting in a waveguide cladded with a nonlinear medium has been predicted to occur when the refractive index of the cladding approaches the effective index of a guided mode. To date, this effect has only been demonstrated experimentally for the TE₁ mode in a glass waveguide cladded with a nonlinear liquid crystal, MBBA. It has been suggested that as the intensity is increased the TE₀ mode will first exhibit a localized maximum, and then degenerate into a surface polariton guided at the interface. We report here the first measurements of optical limiting of the te0 mode in GaAs/AlGaAs MQW cladded waveguides. The waveguide structure consists of a 0.4-μm thickness of a GaAs/Ga_0.94Al_0.06 As (100A/100A) superlattice grown by molecular beam epitaxy on a 1.2-μm GaAs/Ga_0.6Al_0.4As (100A/100) MQW substrate layer. At milliwatt power levels the output power of the TE₀ mode polarized parallel to the MQW layers saturates and then falls off with increasing input power. The TM₀ mode polarized perpendicular to the MQW layers does not show these effects. Low power absorption coefficients for the TE₀ mode range from 150 cm^–1 at 864 nm to 20 cm^–1 at 875 nm. Assuming a simple theory of the intensity-dependent waveguide cutoff, a nonlinear index of n₂ = 1 × 10^–6 cm²/W is predicted.

© 1986 Optical Society of America