Observation of optical states below the light cone with compound lattices

For optical systems, periodic dielectric materials could mold the flow of light, producing abundant attractive properties. Analogous with the electrical bandstructure of solid materials, the dispersion of the optical states of photonic structures are essential to characterize the optical properties, while those states below the light cone are not detectable by far-field measurement experimentally. A method for far-field detection has been developed for observing states below the light cone with compound lattices. The basic mechanism involved is that periodic weak scattering leads to band folding, making the states out of the light cone to occur inside. By using polarization-resolved momentum-space imaging spectroscopy, the band structures and iso-frequency contours of plasmonic lattices with different dimensions and symmetries are experimentally mapped out in good agreement with the simulation. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement