Characterization of photonic crystal coupling to and from guided light by absorbance

filmswhosesurfacewasimprintedwithatwo-dimen-sional (2-D) square shaped photonic crystal with different pattern depths (from 20 to 61 nm). Theaim ofthiswork is todevelopa straightforward methodtocharacterizethe PhCefficiencyonlightextraction. Transmission spectra of the patterned areas as obtained using a routine spectrometerexhibit peaks evidencing the coupling by the photonic crystal structure of free-space light withguided modes within the film, in good agreement with 2-D rigorous-coupled wave analysis(RCWA)simulations.Asexpected,thedeeperthepatterndepth,thestrongerthecouplingbetweenthe guided light and the photonic crystal. RCWA simulations allow evaluating quantitatively theextraction length, characteristic of the efficiency of light extraction, from the transmission spectra,in good agreement with direct measurements.