Design of(GO/TiO2)N one-dimensional photonic crystal photocatalysts with improved photocatalytic activity for tetracycline degradation

(GO/TiO2)N(GO represents graphene oxide,and N represents the period number of alternate superposition of two dielectrics)onedimensional photonic crystal with different lattice constants was prepared via the sol–gel technique,and its transmission characteristics for photocatalysis were tested.The results show that the lattice constant,filling ratio,number of periodic layers,and incident angle had effects on the band gap.When the lattice constant,filling ratio,number of periodic layers,and incident angle were set to 125 nm,0.45,21,and 0°,respectively,a gap width of 53 nm appeared at the central wavelength(322 nm).The absorption peak of the photocatalyst at 357 nm overlapped the blue edge of the photonic band gap.A slow photon effect region above 96%reflectivity appeared.The degradation rate of tetracycline in(GO/TiO2)N photonic crystal was enhanced to 64%within 60 min.Meanwhile,the degradation efficiency of(GO/TiO2)N one-dimensional photonic crystal was effectively improved compared with those of the GO/TiO2 composite film and GO/TiO2 powder.

Description and reconstruction of one-dimensional photonic crystal by digital signal processing theory

A method of describing one-dimensional photonic crystals （1DPCs） based on Z-domain digital signal processing theory is presented. The analytical expression of the target band gap spectrum in the digital domain is obtained by the autocorrelation of its impulse response. The feasibility of this method is verified by reconstructing two simple 1DPC structures with a target photonic band gap obtained by the traditional transfer matrix method. This method provides an effective approach to function-guided designs of interference-based band gap structures for photonic applications.

Frequency bands of negative refraction in finite one-dimensional photonic crystals

We have discussed theoretically the negative refraction in finite one-dimensional （1D） photonic crystals （PCs） composed of alternative layers with high index contrast. The frequency bands of negative refraction are obtained with the help of the photonic band structure, the group velocity and the power transmittance, which are all obtained in analytical expression. There shows negative transverse position shift at the endface when negative refraction occurs, which is analysed in detail.

Theoretical study on the photonic band gap in one-dimensional photonic crystals with graded multilayer structure

We theoretically investigate the photonic band gap in one-dimensional photonic crystals with a graded multilayer structure. The proposed structure constitutes an alternating composite layer （metallic nanoparticles embedded in TiO2 film） and an air layer. Regarding the multilayer as a series of capacitance, effective optical properties are derived. The dispersion relation is obtained with the solution of the transfer matrix equation. With a graded structure in the composite layer, numerical results show that the position and width of the photonic band gap can be effectively modulated by varying the number of the graded composite layers, the volume fraction of nanoparticles and the external stimuli.

Confinement of Bloch surface waves in a graphene-based one-dimensional photonic crystal and sensing applications

Bloch surface waves（BSWs） are excited in one-dimensional photonic crystals（Ph Cs） terminated by a graphene monolayer under the Kretschmann configuration. The field distribution and reflectance spectra are numerically calculated by the transverse magnetic method under transfer-matrix polarization, while the sensitivity is analyzed and compared with those of the surface plasmon resonance sensing method. It is found that the intensity of magnetic field is considerably enhanced in the region of the terminated layer of the multilayer stacks, and that BSW resonance appears only in the interface of the graphene and solution. Influences of the graphene layers and the thickness of a unit cell in Ph Cs on the reflectance are studied as well. In particular, by analyzing the performance of BSW sensors with the graphene monolayer,the wavelength sensitivity of the proposed sensor is 1040 nm/RIU whereas the angular sensitivity is 25.1°/RIU. In addition,the maximum of figure of merit can reach as high as 3000 RIU^-1. Thus, by integrating graphene in a simple Kretschmann structure, one can obtain an enhancement of the light–graphene interaction, which is prospective for creating label-free,low-cost and high-sensitivity optical biosensors.

Ultra-narrow bandwidth optical filters consisting of one-dimensional photonic crystals with anomalous dispersion materials

We present a new type of optical filter with an ultra-narrow bandwidth and a wide field-of-view （FOV）. This kind of optical filter consists of one-dimensional photonic crystal （PC） incorporating an anomalous-dispersion-material （ADM） with, for instance, an anomalous dispersion of 6P3/2←6S1/2 hyperfine structure transition of a caesium atom. The transmission spectra of optical filters are calculated by using the transfer-matrix method. The simulation results show that the designed optical filter has a bandwidth narrower than 0.33GHz and a wide FOV of ±30°as well. The response of transmission spectrum to an external magnetic field is also investigated.

Band structures analysis of one-dimensional photonic crystals using plane wave expansion

A theoretical analysis is made, using plane wave expansion, on how the width of the first three band gaps is influenced by filling ratio, dielectric constant ratio, and periodic width in one-dimensional photonic crystals （PhCs）. From simulation and analysis, there are one, two, and three peak points on the first, second and third band gaps respectively with the changes of filling ratio un- der fixed dielectric constant ratio. When filling ratio is fixed, the bandwidth of the first band gap consistently increases with dielectric constant ratio. However, no similar trend is observed in the second and the third band gaps. Because of scaling properties, varying periodic width does not alter the relative bandwidth.

Thermal tunable one-dimensional photonic crystals containing phase change material

To obtain the adjustable photonic crystals (PCs), we numerically investigate one-dimensional (1D) PCs with alternating VO2 and SiO2 layers through transfer matrix method. The dispersion relation agrees well with the transmittance obtained by the finite element calculation. Tunable band gaps are achieved with the thermal stimuli of VO2, which has two crystal structures. The monoclinic crystal structure VO2 (R) at low temperature exhibits insulating property, and the high temperature square rutile structure VO2 (M) presents metal state. Concretely, the bandwidth is getting narrower and red shift occurs with the higher temperature in VO2 (R)/SiO2 PCs structure. Based on the phase change characteristics of VO2, we can flexibly adjust the original structure as VO2 (R)/VO2 (M)/SiO2. By increasing the phase ratio of VO2 (R) to VO2 (M), the band gap width gradually becomes wider and blue shift occurs. The discrete layers of gradient composites on the dispersion of 1D PCs are also investigated, which enhances the feasibility in practical operation. Thus, our proposed thermal modulation PCs structure paves a new way to realize thermal tunable optical filters and sensors.

High-Q cavity based on gradated one-dimensional photonic crystal

A high quality-factor （Q） cavity based on a one-dimensional （1D） photonic crystal with gradated elliptical holes was designed using FDTD simulation. Different gradient profiles of the mirror holes were found to correspond to different Q- values of the cavities. A simple strategy is proposed to construct high-Q cavities by using an S-shaped gradient profile for the elliptical holes＇ minor axes, such as a cosine function or Gaussian function. Using such a strategy, a Q value exceeding two million is obtained with only ten mirror holes in a cavity.

Enhancement of Phase Matching Ability in One-Dimensional Photonic Crystal through Plasma Materials

We have theoretically studied the modal dispersion equation and effective refractive index of one-dimensional plasma photonic crystals (1-D PPCs) having different materials in one unit cell. The dispersion relations related for such structure is derived by solving Maxwell’s equation using the transfer matrix method. It is found that the presence of plasma in a unit cell enhanced the phase matching ability and provides additional degree of freedom to control phase matching condition compared to the conventional one-dimensional photonic crystals (1-D PCs).

Investigation of Photonic Band Gap in Si-Based One-Dimensional Photonic Crystal

A one-dimensional silicon based photonic crystal with nonlinear defect layers is examined. The linear and nonlinear optical properties are analyzed. The transmission spectrum was obtained by applying the optical transfer matrix formalism to the photonic crystal. The various transmittance peaks obtained with the defect layers are investigated. The nature of the transmittance peak is analyzed with the number of defect layers.

Finite One-Dimensional Photonic Crystal with Gaussian Modulation: Transmission and Escape

This paper studied the transmission coefficient and escape frequencies in a system of planar dielectric layers where the refractive index changes from one layer to another through a Gaussian function. The wave equation with normal incidence is analyzed. For the calculations, the transfer matrix formalism is used. In a previous work, the transmission and escape problem for Gaussian electronic superlattices is investigated. Now it studied the electromagnetic modes for a system formed by layers where the refractive index of the structure is modulated by a Gaussian function. The system presents transparency bands of transmission and gaps without transmission. The escape frequencies are situated near these transparency bands but they do not coincide with them. is the frequency (mode) and Γdescribes the width of the states. For these systems, the escape states are very wide. A non Gaussian system presents resonance peaks in the transmission and the escape states are narrow. The formation of transparency bands in the transmission for a Gaussian system is attributed to the widening of the escape states.

Method of measuring one-dimensional photonic crystal period-structure-film thickness based on Bloch surface wave enhanced Goos–H?nchen shift

This paper puts forward a novel method of measuring the thin period-structure-film thickness based on the Bloch surface wave(BSW) enhanced Goos–Hanchen(GH) shift in one-dimensional photonic crystal(1DPC). The BSW phenomenon appearing in 1DPC enhances the GH shift generated in the attenuated total internal reflection structure. The GH shift is closely related to the thickness of the film which is composed of layer-structure of 1DPC. The GH shifts under multiple different incident light conditions will be obtained by varying the wavelength and angle of the measured light, and the thickness distribution of the entire structure of 1DPC is calculated by the particle swarm optimization(PSO) algorithm.The relationship between the structure of a 1DPC film composed of TiO_(2) and SiO_(2) layers and the GH shift, is investigated.Under the specific photonic crystal structure and incident conditions, a giant GH shift, 5.1 × 10^(3) times the wavelength of incidence, can be obtained theoretically. Simulation and calculation results show that the thickness of termination layer and periodic structure bilayer of 1DPC film with 0.1-nm resolution can be obtained by measuring the GH shifts. The exact structure of a 1DPC film is innovatively measured by the BSW-enhanced GH shift.

Flexible one-dimensional photonic crystal films composed of chalcogenide glass and water-soluble polymer for curvature sensing

Curvature sensing plays an important role in structural health monitoring,damage detection,real-time shape control,modification,etc.Developing curvature sensors with large measurement ranges,high sensitivity,and linearity remains a major challenge.In this study,a curvature sensor based on flexible one-dimensional photonic crystal(1D-PC)films was proposed.The flexible 1D-PC films composed of dense chalcogenide glass and water-soluble polymer materials were fabricated by solution processing.The flexible 1D-PC film curvature sensor has a wide measurement range of 33-133 m-1and a maximum sensitivity of0.26 nm/m^(-1).The shift of the transmission peak varies approximately linearly with the curvature in the entire measurement range.This kind of 1D-PC film curvature sensor provides a new idea for curvature sensing and measurement.

Omni-directional mirror for visible light based on one-dimensional photonic crystal

The omni-directional reflection characteristics of one-dimensional photonic crystals composed of Ta2O5/MgF2 multi-quantum well （MQW） are studied using the transfer matrix method. An omnidirectional reflector consisting of three and four Ta2O5/MgF2 MQWs is investigated. Results show that the photonic band gap of the photonic crystal composed of three and four Ta2O5/MgF2 MQWs, which are within the wavelength ranges of 402-712 and 412-1,023 nm, respectively, could cover the entire visible region. The relationship among the width of the band gap, its location, reflectivity rate, and incident angle of the incident light is analyzed. The optimal structural parameters of the MQW of the omni-directional reflector in the visible region are also calculated. The calculations provide a guide for the design of omni- directional reflection devices in the visible region.

One-Dimensional InP-Based Photonic Crystal Quantum Cascade Laser Emitting at 5.36μm

An InP-based one-dimensional photonic crystal quantum cascade laser is realized. With photo lithography instead of electron beam lithography and using inductively coupled plasma etching, four-period air-semiconductor couples are defined as Bragg reflectors at one end of the resonator. The spectral measurement at 80K shows the quasi-continuous-wave operation with the wavelength of 5.36μm for a 22gm-wide and 2mm-long epilayer-up bonded device.

Properties of single and multiple defect modes in one-dimensional photonic crystals containing left-handed metamaterials

Wave propagation is studied in structures consisting of alternate left- and right-handed layers. Bragg gap and zero-n gap appear in different frequency regions of the structure. The periodicity of the structure is broken by simply reversing the order of the layers in one half of the structure, resulting in defect modes located inside the zero-n gap and Bragg gap. These modes can be made very narrow by adding more layers in the structure. The defect mode located inside the zero-n gap is sensitive to the symmetry of the structure and insensitive to the angle of incidence of the incoming radiation. Multiple modes are also generated inside the gaps by repeating the structural pattern. Thus, a simple structure can be used for single and multiple modes that are imDortant for different applications.

Controlling the Bandgaps of One-Dimensional TiO2/SiO2, TiO2/SnO2, and SiO2/SnO2 Photonic Crystals Using the Transfer Matrix Method

One-dimensional photonic crystals (1D PhCs) have a unique ability to control the propagation of light waves, however certain classes of 1D oxides remain relatively unexplored for use as PhCs. Specifically, there has not been a comparative study of the three different 1D PhC structures to compare the influence of layer thickness, number, and refractive index on the ability of the PhCs to control light transmission. Herein, we use the transfer matrix method (TMM) to theoretically examine the transmission of 1D PhCs composed of layers of TiO2/SiO2, TiO2/SnO2, SiO2/SnO2, and combinations of the three with various top and bottom layer thicknesses to cover a substantial region of the electromagnetic spectrum (UV to NIR). With increasing layer numbers for TiO2/SiO2 and SiO2/SnO2, the edges became sharper and wider and the photonic bandgap width increased. Moreover, we demonstrated that PhCs with significantly thick TiO2/SiO2 layers had a high transmittance for a wide bandgap, allowing for wide-band optical filter applications. These different PhC architectures could enable a variety of applications, depending on the properties needed.

Effective permittivity and permeability of one-dimensional dielectric photonic crystal within a band gap

We take a finite dielectric photonic crystal as a homogeneous slab and have extracted the effective parameters. Our systematic study shows that the effective permittivity or permeability of dielectric photonic crystal is negative within a band gap region. This means that the band gap might act as ε-negative materials （ENMs） with ε 〈 0 and μ 〉 0, or μ-negative materials （MNMs） with ε 〉 0 and μ 〈 0. Moreover the effective parameters sensitively rely on size, surface termination, symmetry, etc. The effective parameters can be used to design full transmission tunnelling modes and amplify evanescent wave. Several cases are studied and the results show that dielectric photonic band gap can indeed mimic a single negative material （ENM or MNM） under some restrictions.

Spontaneous transition of one-dimensional plasma photonic crystal's orientation in a dielectric barrier discharge

A novel one-dimensional plasma photonic crystal whose crystal orientation can change spontaneously is demonstrated using a dielectric barrier discharge with two liquid electrodes. The orientation of the plasma photonic crystal will vary from transverse to longitudinal or vary from longitudinal to transverse and then revert to longitudinal by self-adjustment, while the experimental conditions are kept fixed. The dispersion relation of these plasma photonic crystals are calculated, and the changes of the photonic band diagrams during the orientation transition are studied.