Fano resonances in prism-coupled square micropillars

We report Fano resonances in the frustrated total internal reflection (TIR) spectra of a prism-coupled square micropillar. Our angle-selective frustrated TIR technique reveals characteristically asymmetric resonance line shapes, which evolve spectrally over approximately a $2\pi$ phase in the far field within a subdegree range of reflection angles. We theoretically model the asymmetric line shapes by the interference between a high-$Q$ resonance that is evanescently coupled and partially confined by TIR, and a coherent background that is total internally reflected at the prism surface without coupling to the micropillar.