More Like this

1. Perfectly-reflecting guided-mode-resonant photonic lattices possessing Mie modal memory

   https://doi.org/10.1364/OE.434359  

   Ko, Yeong_Hwan; Razmjooei, Nasrin; Hemmati, Hafez; Magnusson, Robert (August 2021, Optics Express)

   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 the 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. 

   more » « less
2. Resonance properties of isolated-particle optical lattices: Antireflection-quenched Mie scattering and Mie modal memory

   https://doi.org/10.1117/12.2607963  

   Magnusson, Robert; Ko, Yeong H.; Razmjooei, Nasrin; Simlan, Fairooz A.; Hemmati, Hafez (March 2022, Proc. SPIE 12010, Photonic and Phononic Properties of Engineered Nanostructures XII)

   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
3. Perfect reflection by dielectric subwavelength particle arrays: causes, implications, and technology

   https://doi.org/10.1117/12.2578953  

   Magnusson, Robert; Ko, Yeong H.; Lee, Kyu J.; Bootpakdeetam, Pawarat; Razmjooei, Nasrin; Simlan, Fairooz A.; Chen, Ren-Jie; Buchanan-Vega, Joseph; Carney, Daniel J.; Hemmati, Hafez; et al (April 2021, Proc. SPIE, Integrated Optics: Devices, Materials, and Technologies XXV)

   García-Blanco, Sonia M.; Cheben, Pavel (Ed.)

   Periodic arrays of resonant dielectric nano- or microstructures provide perfect reflection across spectral bands whose extent is controllable by design. At resonance, the array yields this result even in a single subwavelength layer fashioned as a membrane or residing on a substrate. The resonance effect, known as guided-mode resonance, is basic to modulated films that are periodic in one dimension (1D) or in two dimensions (2D). It has been known for 40 years that these remarkable effects arise as incident light couples to leaky Bloch-type waveguide modes that propagate laterally while radiating energy. Perfect reflection by periodic lattices derives from the particle assembly and not from constituent particle resonance. We show that perfect reflection is independent of lattice particle shape in the sense that it arises for all particle shapes. The resonance wavelength of the Bloch-mode-mediated zero-order reflectance is primarily controlled by the period for a given lattice. This is because the period has direct, dominant impact on the homogenized effective-medium refractive index of the lattice that controls the effective mode index experienced by the mode generating the resonance. In recent years, the field of metamaterials has blossomed with a flood of attendant publications. A significant fraction of this output is focused on reflectors with claims that local Fabry-Perot or Mie resonance causes perfect reflection with the leaky Bloch-mode viewpoint ignored. In this paper, we advance key points showing the essentiality of lateral leaky Bloch modes while laying bare the shortcomings of the local mode explanations. The state of attendant technology with related applications is summarized. The take-home message is that it is the assembly of particles that delivers all the important effects including perfect reflection. 

   more » « less
4. Resonant reflection by microsphere arrays with AR-quenched Mie scattering

   https://doi.org/10.1364/OE.427982  

   Razmjooei, Nasrin; Ko, Yeong_Hwan; Simlan, Fairooz_Abdullah; Magnusson, Robert (June 2021, Optics Express)

   Periodic guided-mode resonance structures which provide perfect reflection across sizeable spectral bandwidths have been known for decades and are now often referred to as metasurfaces and metamaterials. Although the underlying physics for these devices is explained by evanescent-wave excitation of leaky Bloch modes, a growing body of literature contends that local particle resonance is causative in perfect reflection. Here, we address differentiation of Mie resonance and guided-mode resonance in mediating resonant reflection by periodic particle assemblies. We treat a classic 2D periodic array consisting of silicon spheres. To disable Mie resonance, we apply an optimal antireflection (AR) coating to the spheres. Reflectance maps for coated and uncoated spheres demonstrate that perfect reflection persists in both cases. It is shown that the Mie scattering efficiency of an AR-coated sphere is greatly diminished. The reflectance properties of AR-coated spherical arrays have not appeared in the literature previously. From this viewpoint, these results illustrate high-efficiency resonance reflection in Mie-resonance-quenched particle arrays and may help dispel misconceptions of the basic operational physics. 

   more » « less
5. Principles of leaky-mode photonic lattices: Band flips and Bloch mode dynamics

   https://doi.org/10.1117/12.2508984  

   Magnusson, Robert; Lee, Sun G.; Lee, Kyu J.; Hemmati, Hafez; Carney, Daniel J.; Bootpakdeetam, Pawarat; Ko, Yeong H. (March 2019, Proceedings Volume 10921, Integrated Optics: Devices, Materials, and Technologies XXIII; 109211E (2019))

   García-Blanco, Sonia M.; Cheben, Pavel (Ed.)

   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. 

   more » « less