Omnidirectional and independently tunable defect modes in fractal photonic crystals containing single-negative materials

The properties and applications of omnidirectional and independently tunable defect modes in fractal photonic crystals containing single-negative materials are demonstrated. The proposed fractal structures can produce as many defect modes as desired by adjusting its structural parameters. The interaction effect between the defect states of such fractal structures is avoided, so the frequency of each defect mode can be tuned independently. Furthermore, these defect modes inside the zero effective-phase gap are insensitive to the incident angle. With perfect transmission, mode controllability and omnidirectional compatibility, these structures open a promising way for designing omnidirectional multichannel filters with specific channels.     

Tunable zero-phase-shift omnidirectional filter consisting of single-negative materials

We theoretically design a heterostructure with which we can achieve a tunable zero-phase-shift omnidirectional filter. The results show that by simply adjusting the thickness of the defect layer of air, we can achieve adjustability of the tunneling mode. We further prove the omnidirectional tunneling modes in the heterostructure consisting of layered single-negative materials and one layer of defect. PACS 42.25.Dd; 42.79.Ci     

周期变截面波导中的多缺陷态*

设计了一种具有对称结构的多缺陷周期变截面波导,并在其Bragg禁带中实现了多缺陷态的产生。研究表明,通过调整缺陷的个数和长度可实现对缺陷态数目的选择和缺陷态中心频率的调谐。另外,改变重复周期个数可对缺陷态的带宽进行调节。通过对各缺陷态的声场分布进一步分析,我们发现声压沿波导中心轴呈对称或反对称分布。对称缺陷态的最大声能量总是向长度较小的缺陷处偏移,而反对称缺陷态则相反,总是向长度较大的缺陷处偏移。利用这种偏移特性可实现对多缺陷态的声场调控。这不仅使我们对声缺陷态的认识更加深入,更有利于功能型声波导器件的发展与应用。     

Multichannel filtering properties of photonic crystals containing single-negative materials

The multichannel filtering properties have been investigated by means of the transfer matrix method in photonic crystals containing two kinds of single-negative materials. Two sets of filtering channels appear simultaneously in the zero effective phase gaps. One is omnidirectional for TE polarization but angle-sensitive for TM polarization, while the other is angle-sensitive for TE polarization but omnidirectional for TM polarization. The resonance modes for different channels can be independently tuned. This structure provides an efficient way to fabricate omnidirectional multichannel filters with independently tunable polarization channels.     

Independently tunable omnidirectional multichannel filters based on the fractal multilayers containing negative-index materials

We propose and demonstrate an independently tunable omnidirectional multichannel filter by combining the advantages of the independently tunable filtering properties of fractal structures and the omnidirectional resonant modes of one-dimensional photonic crystals containing negative-index materials. Compared to the conventional multichannel filters, each channel of the proposed filter can be tuned separately, and the frequency position of the filter is insensitive to the incident angle of light. It thus provides a simple way for designing omnidirectional multichannel filters with specific channels.     

Tunable Omnidirectional Surface Plasmon Resonance in Cylindrical Plasmonic Structure

The tunable omnidirectional surface plasmon resonance in the optical range is theoretically demonstrated in a cylindrical plasmonic crystal by using rigorous coupled-wave analysis. The cylindrical plasmonic crystal consists of an infinite chain of two-dimensional cylindrical metal--dielectric-dielectric-metal structures. The dispersion relation of the cylindrical plasmonic crystal is obtained by calculating the absorptance as a function of a TM-polarized incident plane wave and its in-plane wave vector. The omnidirectional surface plasmon resonance can be tuned from UV region to visible region by adjusting the thickness of the cylindrical dielectric layers. The absorption spectrum of the infinite chain of nanocylinders is also investigated for comparison.     

Tunable Pair Transmission in One-Dimensional Photonic Crystals Consisting of Single-Negative Materials

We study the transmission of one-dimensional photonic crystals consisting of single-negative permittivity and single-negative permeability media by using transfer matrix method. A pair of transmission modes is found in the gap. The transmission modes are dependent only on the ratio of the thicknesses of the two alternating layers. The separation of a pair of transmission modes can be tuned by varying the thickness of the defect layer or the ratio of thicknesses of the two alternating layers.     

Tunable optical switch based on two orthogonal line defect waveguides

The transmission characteristics of a 2-dimensional (2D) square lattice photonic crystal waveguide (PCW) with an additional perpendicular line defect are investigated by the plane wave expansion method (PWM) and the finite difference time domain (FDTD) method. From simulation results and theoretical analysis, it is found that changing the refractive index of the dielectric columns in the additional line defect can effectively adjust the light transmission through the PCW. The working mechanism can be boiled down to either the excitation of a single defect mode or the contra-directional coupling of the two defect modes. And this mechanism can be used to design other tunable optical devices.     

多个单负材料缺陷一维光子晶体的孪生缺陷模

分析了含有多个单负材料缺陷层的一维光子晶体中缺陷模的性质。在两种单负(负介电常量或负磁导率)材料交替堆叠形成的一维光子晶体中,掺入了多个周期排列的单负材料缺陷层,得到在该光子晶体的零有效相位(zero-effective phase)带隙内存在孪生缺陷模。通过改变缺陷的数目或缺陷层的厚度,可调节缺陷模的频率间隔,但缺陷模的数目总保持为两个。计算结果显示,该孪生缺陷模的频率对入射角度的依赖较弱;随着入射角度的改变,缺陷模频率的相对改变量总保持在0.03以下。此外,对应缺陷模频率的电场在该光子晶体中传播时,将被强烈地局域在缺陷层与周期结构的交界面上。     

Efficient omnidirectional couplers achieved by anisotropic photonic crystal waveguides

Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated omnidirectional couplers in two-dimensional anisotropic PC structures. The anisotropic PC coupler composed of an anisotropic-dielectric cylinder in air is studied by solving Maxwell's equations using the plane wave expansion method and finite-difference time-domain method. The photonic band structures are found to exhibit absolute bandgaps for the square lattices. Numerical simulations show that the incident light-waves at both transverse electric and transverse magnetic modes have efficient coupling in anisotropic PC coupler with square lattices. The guided modes and coupling length are analyzed by considering various line defect anisotropic PC waveguides and interaction regions of couplers. Such a mechanism of omnidirectional coupling should open up a new application for designing components in photonic integrated circuits.     

Rapid Communication: $$\Delta v=2$$ seniority changing transitions in yrast $$3^-$$3- states and $$B(\textit{E}3)$$B(E3) systematics of Sn isotopes

Using the transfer matrix method, the effect of temperature on one-dimensional (1D) nanostructure photonic crystal with coupled defects has been investigated. One of the layers of this structure is silver. The complex refractive index of silver is dependent on temperature and wavelength. This structure is tunable with temperature and incident angle. It is found that the number of defect modes is equal to the number of coupled defects in all incident angles for both polarizations. Also by increasing the temperature, due to dissipation, the wavelength of the defect modes increases and the height of the defect modes decreases. The wavelengths of defect modes depend linearly on temperature for both polarizations in all incident angles.     

The peculiarities of radiation of chiral photonic crystals with isotropic defect layer

The peculiarities of defect modes and reflection spectra of chiral photonic crystals (CPC) with an isotropic defect for various thicknesses of the defect layer were investigated. The peculiarities of the spectra of photonic density of the state (DOS) and those of the intensity at the center of the defect were investigated, too. It was shown that there is one more possibility of tuning of laser emission - by the change of the defect layer thickness - in CPCs doped with laser dyes (with resonance atoms) and with an isotropic defect. It was shown that the given system can work as a tunable narrow-band filter (or mirror) with tunable wavelength width and tunable location of frequency of the complete transmittance (reflection) band. The radiation peculiarities of these systems were discussed. It was shown that in certain conditions an anomalous strong radiation can be observed for defect modes, and low-threshold laser generation is possible, again, for these modes. It was also shown that radiation suppression is possible for defect modes. The peculiarities of group velocity, group velocity dispersion and non-reciprocity were studied.     

Impurity effects in graphene

Polarization-independent and omnidirectional tunable bandpass filters have been proposed and demonstrated. It is seen that a bilayer period structure composed of single-negative materials can act as a tunable filter, which can be changed from a filter with two symmetrical passband to one with a single pass bandpass, or from one with a wide to one with a narrow pass band. Moreover, the proposed filter is insensitive to the incident angle and polarization of light, which is an omnidirectional, polarization-independent filter for incidence angles between 0° to 90°.     

远红外窄带滤光片厚度的鲁棒性分析

鉴于在制备过程中存在介质层厚度的随机扰动,计算了远红外窄带滤光片厚度的鲁棒性。结果表明:当随机度小于0.05时,窄带滤光片全向带隙和带隙率变化不大,但缺陷层的透射率只有原来的1/3左右;当随机度大于0.1时,随着厚度的随机扰动逐渐增大,窄带滤光片的全向带隙和带隙率都逐渐减小;当随机度达到0.2时,窄带滤光片的第一个全向带隙消失,第二个全向带隙向短波方向偏移明显,缺陷层的透射率也只有原来的1/3左右;当随机度达到0.5时,窄带滤光片的两个全向带隙全部消失。制备了一种远红外窄带滤光片,其结果较好地验证了厚度的随机扰动对滤光片的影响。     

Multiple omnidirectional resonances in a metamaterial sandwich

Multiple omnidirectional resonances are found in a sandwich structure consisting of a left-handed metamaterial cavity and two single-negative-permittivity reflection walls. These resonances appear because the phase shift of left-handed metamaterial can cancel the reflection phase shift of single-negative-permittivity metamaterials at every incidence angle. By using such particular structure, a kind of structure possessing multiple omnidirectional resonances in both polarizations has been designed. In addition, issues associated with energy loss are discussed.     

喇叭型开口光子晶体波导的传输谱研究

设计一种喇叭型开口二维光子晶体波导,利用时域有限差分法计算波导传输谱图。模拟结果表明：通过改变开口处光子晶体椭圆点缺陷的结构,传输谱图中将出现相应变化的缺陷模,可用于实现频率可调的窄带光子晶体滤波器。     

Polarization- and direction-independent defect modes in a wide incident-angle range within Bragg gaps by photonic heterostructures containing negative-index materials

We propose a type of photonic heterostructure by combining dielectric one-dimensional (1D) defective photonic crystals (PCs) and magnetic 1D defective PCs. Both of the two PCs consist of alternating positive-index-material (PIM) layers with a negative-index-material (NIM) defect layer. It is demonstrated by transfer matrix method that there is a polarization- and direction-independent defect mode in a wide incident-angle range within Bragg gaps in the heterostructure. The field distributions prove that the dielectric 1D defective PC benefits to achieve the approximately omnidirectional defect mode for TE waves while the magnetic 1D defective PC benefits for TM waves. Such a structure is useful for designing polarization-independent and omnidirectional or large incident angle narrow-passband filters in optical devices.     

基于含单负材料光量子阱结构的全向多通道滤波器

分析了含单负材料的光量子阱结构中的振荡透射模的性质.用两种单负（负介电常量或负磁导率）材料交替周期堆叠形成的两个光子晶体构造了一维光量子阱结构,该结构中仅其中一个光子晶体含有零有效位相带隙.数值计算结果发现,在零有效位相带隙内存在振荡透射模.通过改变井区域光子晶体内单负材料层的厚度及周期数,振荡透射模的数目、频率及频率间隔均可调节.振荡透射模对入射角度的依赖均很弱;随着入射角度的改变,缺陷模频率的相对改变量保持在0.02以下.该研究结果可用于设计多通道全向滤波器.     

Photonic crystal narrow filters with two neighboring waveguides and a semiconducting point defect

A tunable filter is demonstrated based on a squared lattice two-dimensional photonic crystal. The filter is formed by a single semiconducting point defect and two neighboring waveguides. Modal properties of the defect modes and the transmittance of the proposed system are analyzed using supercell method and finite difference time domain method, respectively. We show that there is a narrow pass band for each temperature between 218 and 240 Kelvin. The peak of the pass band transmittance and the frequency can be highly tunable with the temperature of an intrinsic semiconducting point defect. Also, we have showed that the frequency and temperature of the desired high transmitted filter do not sensitive on the cavity size.     

Multichannel and omnidirectional transparency in periodic metamaterial layers

Multichannel and omnidirectional transmission can be realized in one-dimensional periodic metamaterial layers, where double-negative materials and single-negative materials are alternately stacked. The proposed structures can produce as many resonance transmission modes as desired by adjusting the number of the periods. Such transmission modes with perfect transmission are robust against incident angles and polarizations. The frequencies and frequency intervals of these modes can be tuned by changing the thicknesses of the metamaterial layers. Composite right/left-handed transmission lines with lumped elements (capacitors and inductors) were used to verify the characteristics of the considered system. Our findings provide an efficient way to select useful multiple channel signals from all directions, and it is useful in optoelectronic device applications.