Optical bulk and surface waves with negative refraction

In materials with negative refraction, the direction of wave propagation is opposite to the direction of the wave vector. Using an approach that characterizes the optical response of a medium totally by a generalized dielectric permittivity, , we discuss the possibility of seeing negative refraction for optical waves in a number of nonmagnetic media. These include bulk waves in organic materials and in gyrotropic materials where additional exciton–polariton waves can have a negative group velocity. It is known that dispersion of surface waves can be engineered by tailoring a surface transition layer. We show how this effect can be used to obtain surface waves with negative refraction.     

Some remarks regarding electrodynamics of materials with negative refraction

In the following article some electrodynamical problems of materials with negative refraction are considered. In contrast to the usual case when the index of refraction is positive, for these sorts of materials many laws and equations must be recorded differently. Special note is taken of the fact that most of the books and textbooks are written with the so-called “nonmagnetic approach”, which is only valid for nonmagnetic materials (μ = 1). This approach is undoubtedly unfit for material with a negative index of refraction.It is shown that materials with simultaneously negative dielectric and magnetic permeabilities undoubtedly must possess the frequency dispersion. Correlation is brought between phase and group velocities for these sorts of materials.The question is considered in detail about the so-called “overcoming of the diffraction limit” by means of plates from materials with a negative factor of refraction. It is shown that this effect is indeed reduced to the problem of matching between source and receiver of radiation. Such matching is possible by spreading the so-called evanescent modes, for which a diffraction limit does not exist. These modes fade within a distance of the order of the wavelength, and only at such a distance is the transfer of picture details that are smaller than the wavelength possible.     

A recipe for making materials with negative refraction in acoustics

A recipe is given for making materials with negative refraction in acoustics, i.e., materials in which the group velocity is directed opposite to the phase velocity. The recipe consists of injecting many small particles into a bounded domain, filled with a material whose refraction coefficient is known. The number of small particles to be injected per unit volume around any point x is calculated as well as the boundary impedances of the embedded particles.     

Nano-optic label-free biosensors based on photonic crystal platform with negative refraction

In this paper, a novel biosensor based on hetero photonic crystal (PC) structures is proposed. The biosensor consists of photonic crystals with negative refraction (PCNR) embedded between two ordinary PC structures. The PCNR is employed in order to produce an image that is as similar as the light source, which is located in the first ordinary PC. Significant enhancement of the image is achieved when a nanocavity is introduced into the PCNR. It is found that the transmission peak shifts when the nanocavity is filled with blood plasma, liquid and dry air. It is shown that by careful selection of the radius of the nanocavity, the sensitivity of the proposed biosensor can be enhanced. The presented PCNR biosensor is investigated by employing the finite-difference time-domain method (FDTD).     

负折射率材料对隐失波的幅度增益

分析了隐失波透过负折射率材料制成的透镜时,可以实现相位的调整,从而实现波的聚焦的原理;另外利用叠加原理(干涉法)及场量匹配法分析了负折射率材料如何实现对隐失波的振幅的放大,得到负折射率材料对隐失波有幅度增益,行波和隐失波都能聚焦成像的结论;并利用传输线理论提出隐失波透过负折射率材料平板时可等效地形成一个LC振荡电路,从而实现对隐失波的幅度增益.     

Energy dispersion relation for negative refraction (NR) materials

A general energy dispersion relation is developed for metamaterials having the negative-refraction (NR) property. It is shown that absorption effects are involved with NR phenomena, and the conditions under which NR occurs are discussed. Simple equations for NR are developed by using Lorentzian models.     

Optical modulator based on negative refractive material

Using negative refractive material slow-wave waveguide, a compact and integrated optical modulator is proposed for the first time to our knowledge. The slow group velocities of light, which are readily achievable in negative refractive material waveguide, can dramatically increase the induced phase shifts caused by small changes in the refractive index. Modulation operation with a 40 μm long negative refractive material slow-wave waveguide of a Mach–Zehnder interferometer (MZI) structure was demonstrated by using finite-element method. The size of the novel optical modulator is 100 times shorter than that of the conventional lithium niobate MZI optical modulator.     

Design of a novel sensor based on tapered photonic crystal with negative refraction structures

We report a novel design of an ultracompact sensor consisting of two-dimension photonic crystal with negative refraction coupled to a taper ended by multicavity structure. It is shown that this system exhibits promising properties in the area of sensing. The presence of nanocavities enables the detection of small amount of analytes. By controlling their radii, a large quality factor, Q is reached. It is demonstrated that the quality factor is a key parameter in determining the sensitivity to the analytes.     

Polarization beam splitters based on a two-dimensional photonic crystal of negative refraction

A two-dimensional metallo-dielectric photonic crystal of negative refraction was designed for the application of polarization beam splitters. To match the refractive index of air, the effective refractive index of the designed photonic crystal is -1 for TE polarization and +1 for TM polarization. Two types of polarization beam splitter are presented.     

Photodetecting and light-emitting devices based on two-dimensional materials

Two-dimensional(2D) materials, e.g., graphene, transition metal dichalcogenides(TMDs), and black phosphorus(BP), have demonstrated fascinating electrical and optical characteristics and exhibited great potential in optoelectronic applications. High-performance and multifunctional devices were achieved by employing diverse designs, such as hybrid systems with nanostructured materials, bulk semiconductors and organics, forming 2D heterostructures. In this review,we mainly discuss the recent progress of 2D materials in high-responsive photodetectors, light-emitting devices and single photon emitters. Hybrid systems and van der Waals heterostructure-based devices are emphasized, which exhibit great potential in state-of-the-art applications.     

Multielement integrated optical devices based on high-refractive-index materials

The effect of an additional high-refractive-index layer on the properties of planar waveguides for multielement integrated optical devices is considered. The conditions for highly efficient coupling (self-coupling) upon beam propagation from the three-layer to the four-layer region are determined. Technological recommendations for the production of optical waveguide beam splitters with an increased number of output elements are given.     

High numerical aperture and low-loss negative refraction based on the fishnet rich anisotropy

In this paper we report both numerical and experimentally high numerical aperture on a mesostructure based on fishnet-like building blocks. Under the indefinite media framework, we are able to identify a negative refraction never cutoff band (3rd band of the extraordinary transmission metamaterial) with low-losses at millimeter-waves. We relate negative refraction with the diffraction modes of the periodic structure. The work is another step forward in the new but rapidly evolving subfield of negative refraction metamaterials by anisotropy. The breadth and utility of this approach suggests that metamaterials at their meso-scale may circumvent the problem associated to narrowness and losses exhibited by negative refractive index media at their subwavelength domain, while still being away from the wavelength scale of electromagnetic band-gap.     

Large negative lateral shifts due to negative refraction

When a thin structure in which negative refraction occurs (a metallo-dielectric structure or a photonic crystal) is illuminated by a beam, the reflected and transmitted beam can undergo a large negative lateral shift. This phenomenon can be seen as an interferential enhancement of the geometrical shift and can be considered a signature of negative refraction.     

Coherent control of negative refraction based on local-field enhancement and dynamically induced chirality

This paper studies the electromagnetic response of a coherently driven dense atomic ensemble to a weak probe.It finds that negative refraction with little absorption may be achieved in the presence of local-field enhanced interaction and dynamically induced chirality.The complex refractive index governing the probe refraction and absorption depends critically on the atomic density,the steady population distribution,the coherence dephasings,and the frequency detunings,and is also sensitive to the phase of the driving field because the photonic transition paths form a close loop.Thus,it can periodically tune the refractive index at a fixed frequency from negative to positive values and vice versa just by modulating the driving phase.Moreover,the optimal negative refraction is found to be near the probe magnetic resonance,which then requires the electric fields of the probe and the drive being on two-photon resonance due to the dipole synchronisation.     

Solution-processed white organic light-emitting devices based on small-molecule materials

We investigated solution-processed films of 4,4′-bis(2,2-diphenylvinyl)-1,1′-bibenyl (DPVBi) and its blends with N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) by atomic force microscopy (AFM). The AFM result shows that the solution-processed films are pin-free and their morphology is smooth enough to be used in OLEDs. We have developed a solution-processed white organic light-emitting device (WOLEDs) based on small-molecules, in which the light-emitting layer (EML) was formed by spin-coating the solution of small-molecules on top of the solution-processed hole-transporting layer. This WOLEDs, in which the EML consists of co-host (DPVBi and TPD), the blue dopant (4,4′-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl) and the yellow dye (5,6,11,12-tetraphenylnaphtacene), has a current efficiency of 6.0 cd/A at a practical luminance of 1000 cd/m², a maximum luminance of 22500 cd/m², and its color coordinates are quite stable. Our research shows a possible approach to achieve efficient and low-cost small-molecule-based WOLEDs, which avoids the complexities of the co-evaporation process of multiple dopants and host materials in vacuum depositions.     

Optical properties of melamine based materials

The melamine based crystalline materials are synthesized. To determine the optical properties the transmittance and reflectance spectra are recorded. The absorption coefficient of the materials is calculated using the recorded transmittance values. From the absorption coefficient values the insulating behavior of all our studied materials is identified. In addition the direct bandgap transition nature of the materials is recognized from the absorption coefficient value. Tauc relation is used to determine the bandgap energy. The bandgap energy values suggest the dielectric nature of the materials and interpretation is given for high dielectric constant values.     

Anomalous lateral beam shift and total absorption due to excitation of surface waves in materials with negative refraction

We studied electromagnetic beam reflection from layered structures that include materials with negative refraction. Excitation of leaky surface waves leads to the formation of anomalous lateral shifts in the reflected beams with single or double peak structures. The presence of reasonable losses within material with negative refraction, besides significant influence on manifestation of the giant lateral shifts, can lead to their total suppression and anomalously high absorption of the incident radiation. If, in addition to the resonant excitation of leaky surface waves, radiation inflow exactly compensates their irreversible damping, total absorption of the incoming radiation can be achieved for moderately wide beams.     

On negative refraction in electron optics

Negative refraction is investigated within the context of both relativistic and non-relativistic electron optics. In fact, starting from the de Broglie wave-particle dualism, the negative refractive index as a function of wavelength is determined for both relativistic and non-relativistic electrons. Comparison with photon optics is done. Negative refractive index averaged over both sufficiently small and sufficiently large wavelength ranges is found to be tending to minus unity and minus infinity, respectively. In addition, the sensitivity to wavelength of the negative refractive index is evaluated.     

Ultrasonic band gaps and negative refraction

The first experimentally observed ultrasonic band gaps in periodic bidimensional composited are reviewed here. The studied basic structure consists of an aluminum alloy plate with a periodic arrangement of cylindrical holes filled with mercury. Localization phenomena in linear and point defects have been observed and an ultrasonic waveguide capable to bend the ultrasonic radiation by 90 degrees has been achieved. We also revisit twinned-square periodic structures for ultrasonic wave bending and splitting. Such devices allow 45 degrees bending of waves, whereas an extreme anomalous refraction law at the grain boundaries has also been experimentally observed. Finally, a preliminary study about the possibility of "left-handed" behaviour in ultrasonic crystals is presented in this work. The device consists of a slab of the above mentioned metallic composite attached to an epoxy wedge. In this system, clues to negative refraction are theoretically shown.