High precision temperature- and energy-dependent refractive index of GaAs determined from excitation of optical waveguide eigenmodes

A GaAs-Al_0.22Ga_0.78As heterostructure was prepared and used as a multimode optical waveguide. Propagation constants for individual modes were measured by exciting one mode at a time via real-space surface grating couplers, and the resulting eigenmode distributions were used to obtain the refractive index of GaAs at a matrix of temperatures and photon energies spanning 40 K<T<300 K and 1.40 eV<hν<1.50 eV. Values for dn/dT and the extrapolated refractive index at T=0 K were also obtained. The dominant error source in these measurements was uncertainty in the angular placement of the sample. These measurements agree well with the few pre-existing temperature-dependent measurements, but are an order of magnitude more precise.