Compact high-resolution spectrometer based on super-prism and local-super-collimation effects of photonic crystal.

We propose a design of the compact high-resolution photonic crystal (PhC) spectrometer with a wide working bandwidth based on both super-prism and local-super-collimation (LSC) effects. The optimizing methods, finding the ideal incident angle and oblique angle of PhC for a wider working bandwidth and ideal incident beam width and PhC size for a certain resolution requirement, are developed. Besides the theoretical work, for the first time, the experiment of such a PhC spectrometer is conducted in the microwave frequency range, and the beam-splitting effects for different frequencies in a wide working bandwidth agree very well with the theoretical predictions.

The generalized method to calculate the real-space winding number for one-dimensional systems with complex multi-band-gap structure.

The topological study of the complicated one-dimensional (1D) systems with multi-band-gap structures, including quasi-crystals (QCs), is very hard since the lack of effective topological invariants to describe the non-triviality of gaps. A generalized method, based on the contracted wave-function, is proposed in this work to calculate the real-space winding number for the complicated 1D systems with multi-band-gap structures. First, the effectiveness of the generalized method is demonstrated to obtain the quantized real-space winding number for the gaps and correctly predict the topological phase transition and the existing fractional charge on the edges for the periodic 4-atoms SSH model (4A-SSH model).

Origin of the frequency-sensitive super-collimation phenomenon from the geometry of band dispersion surface for two-dimensional photonic crystals.

Frequency-sensitive super-collimation (FSSC) is a novel dispersion phenomenon of photonic crystals (PhCs) that can realize the beam collimating propagation with very high frequency sensitivity. In order to deeply investigate the origin and the stability of FSSC phenomenon in a wide parameter space, we study the geometry of dispersion surface in detail. Four features for the special geometry of dispersion surface with FSSC are found for rectangular PhCs.

New dynamical nonlinear mechanism, a way to enhance nonlinear efficiency and detect ultrafast electronic processes in photonic crystals.

We quantitatively investigate the energy efficiency and the possibility of detecting the electronic ultrafast processes of a new dynamical nonlinear mechanism suitable for the nonlinear photonic crystal switching effect with femtosecond pumping. It is found that the energy efficiency of the new dynamical nonlinear mechanism is considerably higher than traditional band-gap shift mechanism, and the characteristics of the transmission curve are related to the parameters of the electronic ultrafast processes. Thus, the dynamical nonlinear mechanism is a new way to enhance the nonlinear efficiency and to indirectly detect the electronic femtosecond or even attosecond processes.

Beam propagation in the photonic crystal of the local super-collimation regions.

We investigate the beam propagation behavior in the photonic crystal (PhC) of the local super-collimation (LSC) regions both theoretically and numerically. A theory based on the cubic dispersion model in the LSC regions is established, which is a powerful tool to predict the beam evolution after a long propagation distance. The numerical experiments are also implemented, whose results agree well with those from our theory.

Hyper collimation ability of two-dimensional photonic crystals.

We theoretically investigate the collimation ability of photonic crystals (PhCs) and present a design of rectangular lattice PhC structure which has ultra-high collimation ability, referred to hyper collimation ability of PhC in this work. The competition between the range and the flatness of a "flat segment" on the PhC equi-frequency contour (EFC) is revealed, so that both should be considered simultaneously if we hope to evaluate the collimation ability of a PhC structure. We introduce a new dimensionless value, the normalized collimation length (NCL), to evaluate the collimation ability of a PhC structure.

Two classes of singularities and novel topology in a specially designed synthetic photonic crystals.

Zak phase and topological protected edge state are usually studied in one-dimensional (1D) photonic systems with spatial inversion symmetry (SIS). In this work, we find that specific classes of 1D structure without SIS can be mapped to a system with SIS and also exhibit novel topology, which manifest as phase cut lines (PCLs) in our specially designed synthetic photonic crystals (SPCs). Zak phase defined in SIS is extended to depict the topology of PCLs after redefinition, and a topological protected edge state is also achieved in our 1D structure without SIS.

Tunable photonic crystal lens with high sensitivity of refractive index.

We design a photonic crystal (PhC) lens whose focal length is highly tunable based on the frequency sensitive super-collimation (FSSC) phenomenon. Theoretically, an analytic expression of the focal length in PhCs is derived. The diffraction could be dramatically changed by modest change in refractive index of the dielectric rods in PhCs, because the sensitivity of the equi-frequency-contours around FSSC to refractive index is several orders larger than that in common bulk material.

Tunable control of electromagnetically induced transparency analogue in a compact graphene-based waveguide.

An easily-integrated compact graphene-based waveguide structure is proposed to achieve an analogue of electromagnetically induced transparency (EIT) effect at terahertz frequencies. The structure is composed of a graphene waveguide and two identical-shape graphene ribbons located parallel on the same side of the waveguide at different distances, in which the closer and the farther ribbons behave as the bright and the dark resonators, respectively. The EIT-like effect is caused by the destructive interference of the two resonators.

Enhanced wavelength sensitivity of the self-collimation superprism effect in photonic crystals via slow light.

We demonstrate that the wavelength sensitivity of a self-collimation superprism in photonic crystals (PhCs) can be greatly improved via slow light. With the help of a saddle point Van Hove singularity, we present an approach to obtain such a wavelength-sensitive self-collimation superprism. Our superprism not only has extremely high wavelength sensitivity, but also can suppress beam divergence, irregular beam generation, and wavelength channel dropout, overcoming the limitations of traditional PhC-based superprisms.

Super-collimation with high frequency sensitivity in 2D photonic crystals induced by saddle-type van Hove singularities.

Using detailed numerical simulations, and theoretical modeling, we predict a new super-collimation operation regime which is very sensitive on frequency. This operation regime is predicted to exist in 2D photonic crystals of dielectric rods in low index media. We explain the physical origin of this operation regime, as well as discuss how it could be of interest for implementation of low-power non-linear devices, novel sensors, as well as low-threshold lasers.

High-efficiency nonlinear platform with usage of metallic nonlinear susceptibility.

A scheme with usage of metallic nonlinearity, especially in generating the surface plasmon polariton (SPP) time-reversal wave (TRW), is investigated. It is composed of a metal film and an attached photonic crystal, in which both a far-field-excitable tunneling mode and an SPP guided mode could exist. Two modes are degenerated, deeply penetrated into metal, well overlapped, and localized.

Characterization of short necklace states in the logarithmic transmission spectra of localized systems.

High transmission plateaus exist widely in the logarithmic transmission spectra of localized systems. Their physical origins are short chains of coupled localized states embedded inside the localized system, which are dubbed as 'short necklace states'. In this work, we define the essential quantities and then, based on these quantities, we investigate the properties of the short necklace states statistically and quantitatively.

Impurity-induced bound states in superconductors with topological order.

The study of classical spins in topological insulators (Liu and Ma 2009 Phys. Rev. B 80 115216) is generalized to topological superconductors.

Cancellation of reflection and transmission at metamaterial surfaces.

Based on analytical derivations and numerical simulations, we show that both reflection and transmission can be canceled at the surface of a metamaterial (MM) with a metal-dielectric stratified structure. Strong anisotropic absorption and the surface direction are found to play important roles in this phenomenon. For the angle between the surface and the layers of MMs above a critical value, only reflection is eliminated and transmission is permitted.

Surface plasmon coupling enhanced dielectric environment sensitivity in a quasi-three-dimensional metallic nanohole array.

An enhanced dielectric environment response is observed in a kind of metallic nanohole arrays which are prepared by metal deposition on a sacrificial two dimensional colloidal crystal template. The periodic metallic structures are composed of interlinked metallic half-shells supported on a planar dielectric substrate. When putting in dielectric matrix of different refractive index, the measured sensitivity of the quasi-three-dimensional metallic nanohole array can reach a value of 1192 nm per refractive index unit which shows a five-fold increase as compared with the metallic structures supported on the template.

Remote control of light behavior by transformation optical devices.

Based on the transformation optics, a general method of light-behavior remote control is proposed. From this method, the important coefficients of a cavity, i.e.

Vertical surface emitting open coupled-cavities based on photonic crystal surface modes.

Two types of vertical surface emitting photonic crystal cavities based on beaming mechanism and coupled surface modes are studied. It is shown that vertical emission with a zero divergence angle and a high quality factor can be easily achieved by the back-to-back cavity design. The periodic modulation to the cavity surface alters nonradiative surface modes into radiative surface modes, and the constructive interference of the radiative waves gives rise to vertical emission and improves the quality of the output beam.

Effects induced by Mie resonance in two-dimensional photonic crystals.

The effects of Mie resonance on the photonic band-gap structure of two-dimensional photonic crystals are investigated in detail. Firstly, we demonstrate the correlation between the band-gap structure and Mie resonance, such as the midgap frequency and the changes in gap width with different cylinder radii. We find that the midgap frequency and the gap width increase linearly and then saturate, before and after the Mie resonance frequency crosses the midgap frequency.

The temporal coherence improvement of the two-dimensional negative-index slab image.

In this letter, we investigate the image field of the quasi-monochromatic random source in the two-dimensional negative-index slab. The prominent temporal-coherence gain of the image is observed in the numerical simulations even when the frequency-filtering effects are very weak. We find that the signals originating from the source will take the different time-"group" retarded time to reach the image location along the different optical paths.

Band structures and band gaps of liquid surface waves propagating through an infinite array of cylinders.

The multiple scattering method is applied to the calculations of band structures of liquid surface waves propagating through an infinite array of vertical cylinders. The influence of the filling fraction on the formation of band gaps is discussed. It is found that there exist complete band gaps for both the square and triangular arrays of cylinders.

Localized random lasing modes and a path for observing localization.

We demonstrate that a knowledge of the density of states and the eigenstates of a random system without gain, in conjunction with the frequency profile of the gain, can accurately predict the mode that will lase first. Its critical pumping rate can also be obtained. It is found that the shape of the wave function of the random system remains unchanged as gain is introduced.