Demonstration of an AlGaAs/GaAs integrable optical correlator using surface-emitting second-harmonic generation

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Abstract
A broadband optical correlator with the potential for integration is demonstrated in a GaAs/AlGaAs waveguide for the first time. The correlator uses the surface emission of a coherently generated second-harmonic signal propagating perpendicularly to the direction of propagation of the fundamental beam. While the fundamental pulse propagates back and forth in a waveguide cavity, it emits a second-harmonic signal normal to the top surface of the waveguide. The variation of this second-harmonic signal across the waveguide cavity yields the pulse width of the fundamental beam. Using this technique, a pulse width of 7 ps is measured for a 100 μW(140 mW) average (peak) power of a compressed mode-locked neodymium:yttrium aluminum garnet laser in a GaAs/AlGaAs ridge waveguide cavity. This integrable technique of correlation has the potential of measuring subpicosecond pulses.