Mid-IR transmission of a large-area 2D silicon crystal

We investigate the spectral transmission of a large-area (10 × 10 mm2) two-dimensional silicon-based photonic crystal (PhC) slab waveguide, which was fabricated by a laser interference lithography (LIL) using a silicon-on-insulator wafer. The slab carries a 1 µm period square pattern of round holes in the 0.5 µm thick silicon top layer. Transmission was recorded over the wavelength range from 1.1 to 2.4 µm, i.e. from the near-infrared single-photon absorption edge of silicon to below the mid-infrared two-photon absorption edge. Under normal incidence, we observe Fano and Fabry-Perot-type transmission resonances, in agreement with predictions based on coupled wave analysis. To determine the quality of the LIL fabrication process, the bandwidth of the transmission peaks is determined from experimental data and compared with results of the finite-difference time-domain analysis.