Measurement of bound states in the continuum by a detector embedded in a photonic crystal

We directly measure optical bound states in the continuum(BICs)by embedding a photodetector into a photonic crystal slab.The BICs observed in our experiment are the result of accidental phase matching between incident,reflected and in-plane waves at seemingly random wave vectors in the photonic band structure.Our measurements were confirmed through a rigorously coupled-wave analysis simulation in conjunction with temporal coupled mode theory.Polarization mixing between photonic crystal slab modes was observed and described using a plane wave expansion simulation.The ability to probe the field intensity inside the photonic crystal and thereby to directly measure BICs represents a milestone in the development of integrated opto-electronic devices based on BICs.