Abstract: It has been recognized that AlGaAs-containing planar waveguides can be advantageously used in all-optical gates for wavelengths in the range 1.2-1.7 .mu.m. In particular, such waveguides can produce in radiation pulses of center wavelength, .lambda..sub.s a phase shift of magnitude .pi. or larger while, at the same time, causing attenuation of the pulse by less than 1/e, provided hc/.lambda..sub.x <E.sub.g /2, where E.sub.g is the bandgap associated with the Al.sub.x Ga.sub.2-31 x As-contianing waveguide. In preferred embodiments .lambda..sub.s and/or x are selected such that [hc/(.lambda..sub.s -.DELTA..lambda.]<E.sub.g /2, where .DELTA..lambda. is chosen such that 99% of the pulse energy is contained in the spectral region .lambda..sub.s .+-..DELTA..lambda..