Interpretation of Fano lineshape reversal in the reflectivity spectra of photonic crystal slabs.

Resonant coupling of light to leaky modes of a photonic crystal slab leads to asymmetric Fano lineshapes in the reflectivity spectra. The generally accepted picture, for a lossless system, is that the sign of the real-valued parameter q controls the asymmetry of a Fano resonance. For the reflectivity of a symmetric slab this situation occurs if the amplitude reflection coefficient of the slab goes through zero. In this article, we show that it is also possible to change the asymmetry of a resonance by angle tuning without reaching a condition of zero amplitude. Moreover, we show that the picture of a real-valued parameter q that controls the asymmetry is incomplete.