Abstract

Nonlinear optical interactions in waveguides utilizing the material’s third-order nonlinear optical susceptibility X⁽³⁾ is of interest for potential application, such as ultrafast optical signal processing¹ and nonlinear optical switching.^2,3 The X⁽³⁾ can significantly modify the coupling via either a prism or grating between a radiative wave and guided mode.³ Previously, the experimental demonstrations have been limited to either poor quality waveguides⁴ or materials with a slow (thermal) response time.⁵ We report both linear and nonlinear optical grating coupling to good quality planar GaAs/AlGaAs waveguides and demonstrated nonlinear optical switching. The planar waveguides used in the experiments (1.7-µm GaAs on 3.0-µm AlGaAs) were epitaxially grown by metal-organic chemical vapor deposition (MOCVD) techniques. A 3300-Å period sinusoidal grating of ≃500-Å amplitude was fabricated on the GaAs surface using holographic lithography and ion milling. The coupling to the guided modes was observed by monitoring the intensity of the reflected collimated beam as a function of incident angle. The propagation length of each waveguide mode was also measured by monitoring the output intensity at the cleaved edge of the waveguide as a function of the propagation distance (by moving the incident beam away from the cleaved edge). A cw mode-locked Q-switched Nd:YAG laser operating at 1.06 µm, which produced a mode-locked pulse train of 150-ps pulses, was the light source. The peak intensity of the unfocused optical pulses at the center of the pulse train is The peak intensity of the unfocused optical pulses at the center of the pulse train ≃1 MW/cm², and the duration of the train is ≃300 ns.

© 1986 Optical Society of America