Band Flips and Bound States in Leaky-Mode Resonant Photonic Lattices

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Abstract title: Band Flips and Bound States in Leaky-Mode Resonant Photonic LatticesNontechnical partA photonic lattice is a periodic structure of materials with differing refractive indices. It is analogous to the familiar crystal lattice possessing a regular atomic arrangement. Photonic lattices effectively reflect, filter, and redirect incident light. Metamaterials constitute a new class of photonic lattices wherein principal performance metrics are controlled by the properties of a collection of subwavelength particles. Periodic and aperiodic metasurfaces and metagratings can be fashioned to provide complex functionality in extremely compact format even as single-layer films. Lossless dielectric media are particularly promising for high-efficiency applications. Thus, there is great interest in exploring metamaterials as building blocks for high-performance photonic devices including metalenses, perfect reflectors, and new types of holograms. Here, we propose to demonstrate new fundamental effects in nanophotonic resonance systems that are connected to asymptotic bound states in the spectral continuum. The new understanding generated under the project may lead to innovative ways to control light. The project provides excellent analytical and experimental experience for undergraduate and graduate students thus supporting the development of the next-generation workforce in photonics technology. If successful, the project will lead to innovative optical engineering ideas with substantial economic benefits and societal value. Technical partThe objective of this research is to conduct research into band flips found to occur in leaky-mode photonic lattices. Their connection with non-leaky photonic states or bound states in the continuum (BIC) is of great interest. We seek solid physical understanding of these band flips and associated bound-state transitions and propose to demonstrate them experimentally with proof-of-concept prototypes. These elements will be fashioned as periodic nanostructures in nanocomposites with nanoimprint lithography allowing perfect control of spatial modulation, harmonic content, and spectral linewidths. We investigate fundamental aspects of the resonance interactions in these devices. The detailed spectral properties including band structure will be measured. Thus, we will treat photonic thin-film lattices supporting resonant leaky modes. Their properties include versatile spectra, polarization effects, substantial resonant Q-factors with strong local fields, and phase control. The band structure is unique supporting a leaky edge and a non-leaky edge for each supported resonant mode if the lattice is symmetric. The non-leaky edge is associated with a bound state in the continuum (BIC), or embedded eigenvalue, currently of great scientific interest. It is possible to control the width of the leaky band gap by lattice design. As a modal band closes, there results a quasi-degenerate state?this state is remarkable as it is possible to transit to it by parametric and material choice as shown in this proposal. It is possible to dither dynamically around this point with band-edge transitions into and out of the BIC dispersion branch. There are associated modulation and tuning possibilities. Using semianalytical and rigorous mathematical methods, we will characterize band flips and BICs relative to lattice harmonic content as this has great effect on the band properties. We will study BIC-generated passbands under leaky-mode band flips for the various mode bands. Moreover, we can implement band flips using double resonance structures with paired leaky-mode devices. When the devices are close to each other, the resonance bands interact via evanescent-wave coupling. This configuration possesses additional interference effects along with the band-transition and BIC properties of the simpler embodiments. Electrically induced coupling in and out of the bound continuum states might be possible. The new band-flip concept proposed here is unexplored with high potential impact in various branches of photonics along with exciting possibilities for new scientific discoveries.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.