The measured reflection spectra of two-dimensional photonic crystal slabs consist of an asymmetric peak on
top of an oscillating background. For p-polarized light, the asymmetry of the peak flips for angles of incidence
beyond Brewster's angle. We explain the observed line shapes with a Fano model that includes loss and use a
waveguide model to predict the resonance frequencies of the photonic crystal slab. Finite-difference time domain
calculations support the model and show that the resonance due to a higher order mode disappears when the
substrate refractive index is increased beyond ns = 2.04. This is readily explained by the cut-off condition of
the modes given by the waveguide model.
We have measured the angle and wavelength dependent transmission of index matched metal hole arrays, and
of arrays with a dielectric pillar in each hole. Index matching enhances the transmission, but also broadens the
resonances due to an enhanced coupling between plasmon and radiation modes. Hole arrays that are covered
with glass or have a glass pillar in each hole are created using an imprinting technique. We observe additional
waveguide modes in the transmission spectra of these arrays and discuss the avoided crossing that we observe
for the hybrid structure with dielectric pillars in the holes.