Resonant periodic nanostructures provide perfect reflection across small or large spectral bandwidths depending on the choice of materials and design parameters. This effect has been known for decades, observed theoretically and experimentally via one-dimensional and two-dimensional structures commonly known as resonant gratings, metamaterials, and metasurfaces. The physical cause of this extraordinary phenomenon is guided-mode resonance mediated by lateral Bloch modes excited by evanescent diffraction orders in the subwavelength regime. In recent years, hundreds of papers have declared Fabry-Perot or Mie resonance to be basis of the perfect reflection possessed by periodic metasurfaces. Treating a simple one-dimensional cylindrical-rod lattice, here we show clearly and unambiguously that Mie resonance does not cause perfect reflection. In fact, the spectral placement of the Bloch-mode-mediated zero-order reflectance is primarily controlled by the lattice period by way of its direct effect on the homogenized effective-medium refractive index of the lattice. In general, perfect reflection appears away from Mie resonance. However, when the lateral leaky-mode field profiles approach the isolated-particle Mie field profiles, the resonance locus tends towards the Mie resonance wavelength. The fact that the lattice fields remember the isolated particle fields is referred here as Mie modal memory. On erasure of the Mie memory by an index-matched sublayer, we show that perfect reflection survives with the resonance locus approaching the homogenized effective-medium waveguide locus. The results presented here will aid in clarifying the physical basis of general resonant photonic lattices.
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Principles of leaky-mode photonic lattices: Band flips and Bloch mode dynamics
We present principles of leaky-mode photonic lattices explaining key properties enabling potential device applications.
The one-dimensional grating-type canonical model is rich in properties and conceptually transparent encompassing all
essential attributes applicable to two-dimensional metasurfaces and periodic photonic slabs. We address the operative
physical mechanisms grounded in lateral leaky Bloch mode resonance emphasizing the significant influence imparted by
the periodicity and the waveguide characteristics of the lattice. The effects discussed are not explainable in terms of local
Fabry-Perot or Mie resonances. In particular, herein, we summarize the band dynamics of the leaky stopband revealing
principal Bragg diffraction processes responsible for band-gap size and band closure conditions. We review Bloch wave
vector control of spectral characteristics in terms of distinct evanescent diffraction channels driving designated Bloch
modes in the lattice.
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- Award ID(s):
- 1809143
- NSF-PAR ID:
- 10247696
- Editor(s):
- García-Blanco, Sonia M.; Cheben, Pavel
- Date Published:
- Journal Name:
- Proceedings Volume 10921, Integrated Optics: Devices, Materials, and Technologies XXIII; 109211E (2019)
- Volume:
- 10921
- Page Range / eLocation ID:
- 109211E-1
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Subwavelength resonant lattices offer a wide range of fascinating spectral phenomena under broadside illumination. The resonance mechanism relies on the generation of lateral Bloch modes that are phase matched to evanescent diffraction orders. The spectral properties and the total number of resonance states are governed by the structure of leaky modes and the mode count. This study investigates the effect of interface modifications on the band dynamics and bound-state transitions in guided-mode resonant lattices. We provide photonic lattices comprising rectangular Si3N4 rods with a liquid film with an adjustable boundary. The band structures and band flips are examined through numerical simulations using the rigorous coupled-wave analysis (RCWA) method and analyzing the zero-order spectral reflectance as a function of the incident angle. The band structures and band flips are examined through numerical simulations, and the influences of the refractive index and the thickness of the oil layer on the band dynamics are investigated. The results reveal distinct resonance linewidths corresponding to different refractive indices of the oil layer. Furthermore, the effect of the oil thickness on the band dynamics is explored, demonstrating precise control over the number of propagating modes within the lattice structure. Theoretical simulations and experimental results are presented for a subwavelength silicon-nitride lattice combined with a liquid film featuring an adjustable boundary. The presence of a relatively thick liquid waveguiding region enables the emergence of additional modes, including the first four transverse-electric (TE) leaky modes, which produce observable resonance signatures. Through experimental manipulation of the basic lattice’s duty cycle, the four bands undergo quantifiable band transitions and closures. The experimental results obtained within the 1400–1600 nm spectral range exhibit reasonable agreement with the numerical analysis. These findings underscore the significant role played by the interface in shaping the band dynamics of the lattice structure, providing valuable insights into the design and optimization of photonic lattices with adjustable interfaces.
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We demonstrate band flip in one-dimensional dielectric photonic lattices presenting numerical and experimental results. In periodic optical lattices supporting leaky Bloch modes, there exists a second stop band where one band edge experiences radiation loss resulting in guided-mode resonance (GMR), while the other band edge becomes a nonleaky bound state in the continuum (BIC). To illustrate the band flip, band structures for two different lattices are provided by calculating zero-order reflectance with respect to wavelength and incident angle. We then provide three photonic lattices, each with a different fill factor, consisting of photoresist gratings on Si3N4sublayers with glass substrates. The designs are fabricated using laser interferometric lithography. The lattice parameters are characterized and verified with an atomic force microscope. The band transition under fill-factor variation is accomplished experimentally. The measured data are compared to simulation results and show good agreement.
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Adibi, Ali ; Lin, Shawn-Yu ; Scherer, Axel (Ed.)Periodic optical lattices consisting of isolated-particle arrays in vacuum are treated with rigorous electromagnetics. These structures possess a wealth of interesting properties including perfect reflection across small or large spectral bandwidths depending on the choice of materials and design parameters. Pertinent spectral expressions have been observed theoretically and experimentally via one-dimensional (1D) and two-dimensional (2D) structures commonly known as resonant gratings, metamaterials, and metasurfaces. The physical cause of perfect reflection and related properties is guided-mode resonance mediated by lateral Bloch modes excited by evanescent diffraction orders in the subwavelength regime. Here, we review recent results on differentiation of local Mie resonance and guided-mode lattice resonance in causing resonant reflection by periodic particle assemblies. We treat a classic 2D periodic array consisting of dielectric spheres. To disable Mie resonance, we apply antireflection (AR) coatings to the spheres. Reflectance maps for coated and uncoated spheres demonstrate that perfect reflection persists in both cases. We find that the Mie scattering efficiency of an AR-coated sphere is greatly diminished. Additionally, in a 1D cylindrical rod-type lattice, we investigate and compare local field profiles in periodic assemblies and in the constituent isolated particles. In general, the lattice and particle resonance wavelengths differ. When the lateral leaky-mode field profiles approach the isolated-particle Mie field profiles, the resonance locus tends towards the Mie resonance wavelength. This correspondence is referred to as Mie modal memory. These fundamentals may help distinguish Mie effects and leaky-mode lattice effects in generating the observed spectra in this class of optical devices while elucidating the basic resonance properties across the entire spectral domain.more » « less
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In the physical description of photonic lattices, leaky-mode resonance and bound states in the continuum are central concepts. Understanding of their existence conditions and dependence on lattice parameters is of fundamental interest. Primary leaky-wave effects are associated with the second stop band at the photonic lattice Γ point. The pertinent band gap is defined by the frequency difference between the leaky-mode band edge and the bound-state edge. This paper address the polarization properties of the band gaps resident in laterally periodic one-dimensional photonic lattices. We show that the band gaps pertinent to TM and TE leaky modes exhibit significantly differentiated evolution as the lattice parameters vary. This is because the TM band gap is governed by a surface effect due to the discontinuity of the dielectric constant at the interfaces of the photonic lattice as well as by a Bragg effect due to the periodic in-plane dielectric constant modulation. We find that when the lattice is thin (thick), the surface (Bragg) effect dominates the Bragg (surface) effect in the formation of the TM band. This leads to complex TM band dynamics with multiple band closures possible under parametric variation. In complete contrast, the TE band gap is governed only by the Bragg effect thus exhibiting simpler band dynamics. This research elucidates the important effect of polarization on resonant leaky-mode band dynamics whose explanation has heretofore not been available.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1117/12.2508984
