Fundamentals and applications of resonant leaky-mode photonic lattices

Nano-and microstructured films with subwavelength periodicity represent fundamental building blocks for a host of device concepts. Whereas the canonical physical properties are fully embodied in a one-dimensional lattice, the final device constructs are often patterned in a two-dimensional slab or film in which case we refer to them as photonic crystal slabs or metasurfaces. These surfaces are capable of supporting lateral modes and localized field signatures with propagative and evanescent diffraction channels critically controlling the response. Local Fabry-Perot and Mie mode signatures are observable by computations within the structural geometry. It is clear that these local modes have no causal effect with all key functionality provided by lateral leaky Bloch modes. The subwavelength restriction of periodicity is usually maintained for effective devices; however, it is also possible to generate interesting spectral behavior when this is not satisfied leading to unexpected device concepts. The dominant second leaky stopband exhibits many remarkable physical properties including band-edge transitions and bound states in the continuum. Multi-resonance effects are observed when Bloch eigenmodes are excited with more than one evanescent diffraction channel with the resulting spectral response clearly understood by invoking this process. In this paper, we discuss these key properties of leaky-mode lattices and present relevant device examples. These include fiber mounted resonant sensors that have been designed, fabricated and tested. Moreover, for potential aerospace applications including imaging and sensing, experimental results on wideband reflectors operating in the mid-IR spectral region spanning from 3 to 13 mu m are presented along with demonstration of their design and fabrication.