Photoluminescence from an active planar optical waveguide made of silicon nanocrystals: dominance of leaky substrate modes in dissipative structures

Samples with the structure of asymmetric planar waveguides are fabricated by implanting Si+ ions with energy of 400 keV and doses from 3 to 6 × 1017 cm−2 into synthetic silica slabs. Broad photoluminescence spectrum is observed when collecting photoluminescence (PL) signal in the direction perpendicular to the plane of waveguides while PL collected from the edge of the sample reveals narrow (FWHM of 10-20 nm) polarization-resolved transverse electric (TE) and transverse magnetic (TM) peaks. This peculiar observation is explained using a theoretical model, developed within the framework of wave optics. The TE and TM modes are identified as radiative leaky modes of the planar waveguide. Conditions under which the narrow modes can be seen in the edge PL spectra are described.