Theoretical investigation of one-dimensional cavities in two-dimensional photonic crystals

We study numerically the features of the resonant peak of one-dimensional (1-D) dielectric cavities in a two-dimensional (2-D) hexagonal lattice. We use both the transfer matrix method and the finite difference time-domain (FDTD) method to calculate the transmission coefficient. We compare the two methods and discuss their results for the transmission and quality factor Q of the resonant peak. We also examine the dependence of Q on absorption and losses, the thickness of the sample and the lateral width of the cavity. The Q- factor dependence on the width of the source in the FDTD calculations is also given.Comment: 25 pages, 8 figure

Breaking transmission symmetry without breaking reciprocity in linear all-dielectric polarization-preserving metagratings

Transmission asymmetry in reciprocal systems offers an appealing alternative to bulkier non-reciprocal implementations for certain applications. Common reciprocal routes to transmission asymmetry of linearly polarized light involve a rotation of its polarization. Here, we explore a different route with a linear all-dielectric metagrating that preserves polarization, while lacking inversion symmetry along the surface-normal direction. Our all-angle transmission calculations reveal an abrupt transition from a symmetric to an asymmetric transmission response that traces the Bragg critical wavelength of higher-order beam emergence as a function of the incident angle. By adopting an analogy between scattering from a multi-port network and the metagrating paradigm we establish why the only necessary condition for transmission symmetry breaking in this class of systems, is the emergence of any higher-order Bragg diffracted beam. We further show how such a transmission symmetry breaking is consistent with reciprocity and also demonstrate the underpinning symmetry-breaking mechanism with a first-principle numerical experiment. Finally, we elucidate on some previous misconceptions regarding transmission symmetry breaking related to the role of the substrate or need for change of diffraction order number at each interface. Our proposed metagrating can exhibit a strong transmission asymmetry, with contrast that can be as high as ~75%, thus underlining its potential as a blueprint for passive asymmetric or non-linear self-biasing non-reciprocal metasurfaces relevant to integrated and active photonics.Comment: 10 pages, 6 figure

Topological analysis of polymeric melts: Chain length effects and fast-converging estimators for entanglement length

Primitive path analyses of entanglements are performed over a wide range of chain lengths for both bead spring and atomistic polyethylene polymer melts. Estimators for the entanglement length N_e which operate on results for a single chain length N are shown to produce systematic O(1/N) errors. The mathematical roots of these errors are identified as (a) treating chain ends as entanglements and (b) neglecting non-Gaussian corrections to chain and primitive path dimensions. The prefactors for the O(1/N) errors may be large; in general their magnitude depends both on the polymer model and the method used to obtain primitive paths. We propose, derive and test new estimators which eliminate these systematic errors using information obtainable from the variation of entanglement characteristics with chain length. The new estimators produce accurate results for N_e from marginally entangled systems. Formulas based on direct enumeration of entanglements appear to converge faster and are simpler to apply.Comment: Major revisions. Developed near-ideal estimators which operate on multiple chain lengths. Now test these on two very different model polymers

First Report for Pathogenity of Cydia Pomonella Granulovirus and Helicoverpa Armigera Nucleopolyhedrovirus to Indian Meal Moth Plodia Interpunctella Hϋbner (Lepidoptera: Pyralidae) in Vitro

The purpose of this study was to examine the for the first time the effect of Cydia pomonella granulovirus and Helicoverpa armigera nucleopolyhedrovirus on the larvae of the Lepidopteran Plodia interpunctella. L3 larvae were tested to see whether they were influenced by the infection of the two entomopathogenic viruses Cydia pomonella granulovirus and Helicoverpa armigera nucleopolyhedrovirus. The experiment lasted seven days. The results showed that the effect of the two Baculoviruses was statistically important in relation to the control. The effect of the virus H. armigera nucleopolyhedrovirus was greater than the effect of the virus C. pomonella granulovirus, and this led us to the assumption that the use of entomopathogenic viruses can play an important role in controlling P. interpunctella larvae. The recorded mortality after 7 days was for larvae treated with C. pomonella granulovirus 33.3 to 86.7%, with H. armigera nucleopolyhedrovirus 53.3 to 93.3% and control mortality was 0.7%. This information may appear particularly useful in the future control of the insect’s populations in the warehouse

Refraction at Media with Negative Refractive Index

We show that an electromagnetic (EM) wave undergoes negative refraction at the interface between a positive and negative refractive index material. Finite difference time domain (FDTD) simulations are used to study the time evolution of an EM wave as it hits the interface. The wave is trapped temporarily at the interface and after a long time, the wave front moves eventually in the negative direction. This explains why causality and speed of light are not violated in spite of the negative refraction always present in a negative index material.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Let

Broadband Mid-IR superabsorption with aperiodic polaritonic photonic crystals

We propose an approach for broadband near-perfect absorption with aperiodic-polaritonic photonic crystals (PCs) operating in the phononpolariton gap of the constituent material. In this frequency regime the bulk polaritonic materials are highly reflective due to the extreme permittivity values, and so their absorption capabilities are limited. However, we are able to achieve absorptance of more than 90%  almost across the entire phonon-polariton gap of SiC with a SiC-air aperiodic one-dimensional(1D)-PC with angular bandwidth that covers the range of realistic diffraction-limited sources. We explore two types of aperiodic PC schemes, one in which the thickness of the SiC layer increases linearly, and one in which the filling ratio increases linearly throughout the structure. We find that the former scheme performs better in terms of exhibiting smoother spectra and employing less SiC material. On the other hand, the second scheme performs better in terms of the required total structure size. We analyze the principles underpinning the broadband absorption merit of our proposed designs, and determine that the key protagonists are the properties of the entry building block and the adiabaticity of the aperiodic sequencing scheme. Further investigation with derivative lamellar sequences,–resulting by interchanging or random positioning of the original building blocks–, underline the crucial importance of the building block arrangement in an increasing order of thickness. If we relax the requirement of near-perfect absorption, we show that an averaged absorption enhancement across the SiC phonon-polariton gap of ~10 can be achieved with much shorter designs of the order of two free-space wavelengths. Our findings suggest that our aperiodic polaritonic PC route can be promising to design broadband electromagnetic absorbers across the spectrum

Phonon-polaritonics: enabling powerful capabilities for infrared photonics

Here, we review the progress and most recent advances in phonon-polaritonics, an emerging and growing field that has brought about a range of powerful possibilities for mid- to far-infrared (IR) light. These extraordinary capabilities are enabled by the resonant coupling between the impinging light and the vibrations of the material lattice, known as phonon-polaritons (PhPs). These PhPs yield a characteristic optical response in certain materials, occurring within an IR spectral window known as the reststrahlen band. In particular, these materials transition in the reststrahlen band from a high-refractive-index behavior, to a near-perfect metal behavior, to a plasmonic behavior – typical of metals at optical frequencies. When anisotropic they may also possess unconventional photonic constitutive properties thought of as possible only with metamaterials. The recent surge in two-dimensional (2D) material research has also enabled PhP responses with atomically-thin materials. Such vast and extraordinary photonic responses can be utilized for a plethora of unusual effects for IR light. Examples include sub-diffraction surface wave guiding, artificial magnetism, exotic photonic dispersions, thermal emission enhancement, perfect absorption and enhanced near-field heat transfer. Finally, we discuss the tremendous potential impact of these IR functionalities for the advancement of IR sources and sensors, as well as for thermal management and THz-diagnostic imaging

Feature issue introduction: Beyond Thin Films: Photonics with Ultrathin and Atomically Thin Materials

Rapid advances in nanotechnology have brought about the realization of material films that may comprise only as little as a few atomic layers. For example, semiconductors and metals of sub-10 nm thicknesses have been realized. Then, the graphene paradigm inspired a plethora of other 2D and quasi-2D materials. In this new era, materials have transcended beyond the traditional thin films to a domain of atomic-scale thicknesses, unleashing vast and unexplored possibilities for light-matter interactions. This Optical Materials Express virtual issue features a collection of thirty-five papers aiming to capture the current state-of-the art, trends and open research directions in photonics with ultrathin and atomically thin materials