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Graduate Student Seminar - 11/15/2013

"Measuring and Exploiting Nonlinearity in Semiconductor Optical Waveguides"

by Jeremiah Wathen

Friday, November 15, 2013 -- 12:00 p.m.
Large Conference Room (1207), Energy Research Facility

Advisor: Professor Thomas Murphy

We present an experimental study of the optical nonlinearity of semiconductor waveguides. Special emphasis is placed on continuous-wave four-wave mixing in bandgap-engineered AlGaAs waveguides, with the intended application of “format-free” all-optical wavelength conversion. By tailoring the bandgap of the AlGaAs alloy to suppress two-photon absorption at telecom wavelengths, we demonstrate four-wave-mixing conversion efficiencies equivalent to the highest achieved in passive silicon nanowires (Idler (OUT) / Signal (IN) = -6.8 dB). Additionally, the efficient wavelength conversion is accompanied by measurable parametric amplification of the input signal; this is the first demonstration of significant continuous-wave parametric amplification in a semiconductor waveguide. Also presented is a new technique to measure the ratio between the imaginary and real parts of the third-order nonlinearity in optical waveguides. Unlike most other methods, it does not depend on precise knowledge of the coupling efficiencies, optical propagation loss, or optical pulse shape. We apply the method to characterize silicon waveguides and AlGaAs waveguides with different alloy concentrations.

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