Enhanced in and out-coupling of InGaAs slab waveguides by periodic metal slit arrays.

We studied the in- and the out-coupling efficiencies of photons with a thin InGaAs slab covered by periodic gold nano-slit arrays, by measuring transmission and photoluminescence (PL) spectra. While the maximum in-coupled photons into the InGaAs slab waveguide were found at dip positions in transmission spectra, the mostly out-coupled photons were observed as peaks in PL spectra. For different periods of slit arrays and incident angles we discussed spectral positions of transmission dips and efficiency of the in-coupling influenced by the absorption coefficient of InGaAs. In PL spectra we measured overall enhanced PL intensities from the InGaAs slab covered by slit arrays compared to that of a bare InGaAs, where the peak positions are determined by the period of slit arrays as well. Our findings are important for designing semiconductors both as an optically passive waveguide and active light emitter.