Independently tunable transmission-type magneto-optical isolators based on multilayers containing magnetic materials

We investigate the magneto-optical (MO) properties of multilayers containing several magnetic defects. Our numerical simulations show that each MO defect mode can be tuned independently by adjusting the structural parameters of magnetic materials. In addition, giant Faraday rotation can be obtained. Our results indicate that the structure may have potential applications for independently tunable multichannel MO isolators.     

Independently tunable multichannel terahertz filters

We numerically demonstrate terahertz multichannel filters with independently tunable defect modes based on fractal photonic crystals. Single defect and multiple defects models are proposed to fabricate the multichannel terahertz filters. The facts that the wave functions of the defect states do not overlap and their bases are orthogonal lead to the independency among the defect modes. The simulated results theoretically provide the principle for fabricating independently tunable multichannel terahertz filters by utilizing one-dimensional photonic crystals with defects.     

Polarization-independent omnidirectional band gaps in heterostructures containing negative-index materials

We proposed a type of heterostructure by combining two photonic crystals (PCs) consisting of alternating negative-index materials and positive-index materials layers. It is demonstrated by transfer matrix method that the proposed structure has a polarization-independent omnidirectional band gap (OBG), which is independent of the incident angle for both TE and TM polarizations. Compared to a single PC, the frequency range of the OBG in a heterostructure can be notably enlarged. Such a structure has potential applications in improving planar microcavities, optical fibers, and Fabry-Pérot resonators, etc.     

Photonic quantum-well structures containing negative-index materials

The properties of photonic quantum-well structures containing negative-index materials are studied theoretically, showing features remarkably better than conventional photonic quantum-well structures. Owning to the zero- gap of one-dimensional photonic crystals containing negative-index materials, the photonic quantum-well structures can be proposed as a multiple channeled filter which is very weak dependent on incident angle and polarization, and insensitive to the thickness disorder of the barrier photonic crystals.     

Aberration-free two-thin-lens systems based on negative-index materials

Since the complete correction of all five monochromatic Seidel aberrations for a singlet lens with random shape or a two-thin-lens system is unprocurable merely by using the conventional positive-index materials both in theory and practice, this paper proposes that when one or both of the two lenses is/are made from negative-index materials, an imaging system composed of a pair of spherical thin lenses is possible to form a real image, in air, free from all five monochromatic Seidel aberrations. The calculated numerical solutions to the structural parameters of such lens systems possessing superior performance are provided and examples of them are illustrated for the given combinations of the two lenses＇ refractive indices, including an ultimately-remote imaging system.     

Zero-averaged refractive-index gaps extension by using photonic heterostructures containing negative-index materials

We show theoretically that the frequency range of the zero-averaged refractive-index gap can be substantially extended in a photonic heterostructure containing negative-index materials. This photonic heterostructure consists of different one-dimensional (1D) photonic crystals. The constituent 1D photonic crystals have to be properly chosen in such a way that their zero-averaged refractive-index gap of the adjacent photonic crystals overlap each other.     

数值研究含有负折射率材料的一维光子晶体的带隙特性

由修正后的传输矩阵理论研究了由单负材料构成的一维光子晶体的带隙特性。发现了此结构的光子晶体中同时存在着全方位带隙和布拉格带隙,且发现A、B层厚度等比例变化时全方位带隙非常稳定;当引入缺陷时,全方位带隙里的缺陷态将随入射角度、A层和B层同比例缩放的变化相对稳定,而布拉格带隙里的缺陷态在频谱域内变化很大。     

Tunable multichannel drop filters based on the two-dimensional photonic crystal with oval defects

Light propagation through the channel filter based on the two-dimensional photonic crystals with oval-rod defects is studied by the finite-difference time-domain method. In addition to the traditional size tuning, shape alteration of the defects from the usual circle to the ellipse offers a powerful approach to tune the resonant frequency of channel-drop filters based on two-dimensional photonic crystals. It is found that the resonant frequency can be flexibly adjusted only by changing the orientation angle of the oval defects. The sensitivity of the resonant frequency to the alteration of the oval rods’ rotation angle is systematically studied. Because the rotation angles of the ellipse can be continuously adjusted, so the channel drop filter based on this kind of defects with different rotation angles is more suitable to the occasion where a large number of output channel filters is need.     

Tunable multichannel filter in photonic crystal heterostructure containing permeability-negative materials

A tunable multichannel filter is demonstrated theoretically based on a one-dimensional photonic crystal heterostructure containing permeability-negative material. The filtering properties of the photonic crystal filter, including the channel number and frequency, can be tuned by adjusting the structure parameters or by a pump laser. The angular response of the photonic crystal filter and the influences of the losses on the filtering properties are also analyzed.     

Omni-reflectance and enhanced resonant tunneling from multilayers containing left-handed materials

We study the oblique transmission through a one-dimensional photonic crystal consisting of alternating slabs made of ordinary and negative refractive index materials, the latter being dispersive. We investigate the angular dependence of the band gap for this multilayer medium. Our results suggest, unlike a conventional Bragg gap, this type of gap exhibits a rather versatile behavior with varying angle of incidence. We find the angle-dependent characteristics for this type of gap can be quite different for different structural parameters of the constituents. Thus, multilayer structures involving left-handed components are very good candidates for band gap engineering. Specifically, we demonstrate for a certain experimentally realizable structure, the existence of a gap region for each individual polarization which survives for incident angles as high as 85 °. Moreover, we show how this structure can also function as a highly efficient polarization splitter. Finally, we investigate the multilayer medium when acting as single or double electromagnetic barrier. We study the tunneling properties of such systems for both types of individual barrier layers—right- and left-handed, respectively. We observe the double barrier exhibits resonant tunneling that depends on the “rightness” of the individual barrier layers.     

Temperature-responded tunable metalenses based on phase transition materials

Once the metalenses are fabricated, the functions of most metalenses are invariable. The tunability and reconfigurability are useful and cost-saving for metalenses in realistic applications. We demonstrate this tunability here via a novel hybrid metalens with the strategic placement of an ultra-thin VO₂ layer. The hybrid metalens is capable of dynamically modulating the focusing intensity of transmitted light at a wavelength of 1550 nm, and demonstrate a 42.28% focusing efficiency of the incident light and 70.01% modulation efficiency. The hybrid metalens' optothermal simulations show an optothermal conversion process of dynamic focusing, and a maximum laser density of 1.76×10³ W/cm² can be handled at an ambient temperature lower than 330 K. The hybrid metalens proposed in this work, a light-dose sensitive tunable smart metalens that can protect other instruments/systems or materials from being damaged, has its specific applications such as in anti-satellite blinding, bio-imaging, etc.     

Broadly wavelength tunable bandpass filters based on long-range surface plasmon polaritons

We report a new kind of broadly tunable optical bandpass filters based on unusual properties of long-range surface plasmon polaritons. A 0.004 variation in the refractive index of the dielectric medium translates into 210 nm of bandpass tuning at telecom wavelengths. The tuning mechanism reported here may be used to create compact and widely tunable optical systems and other plasmonic components with broadly tunable optical response.     

基于可拉伸材料的动态调谐彩色滤波器

可动态调谐的集成光学器件在成像、显示等领域拥有良好的应用前景。提出一种新颖的基于可拉伸衬底的动态调谐氧化钛-聚合物微纳结构滤波器,该结构表面可利用电子束蒸发沉积与剥离技术制作, 使用时域有限差分法(FDTD)模拟优化结构参数, 分析了滤波效果及其物理规律。分析结果表明:通过拉伸衬底,所设计的滤波器结构能够在可见光波段上实现全波段滤波,并且具有超高反射率,反射率大部分处于95%以上,最高可达99.1%。这为利用沉积剥离技术制备动态调谐滤波器阵列的实验提供了理论支持。相较于静态调谐的滤波器一旦定型即结构无法更改的缺点,提出的动态调谐结构在器件定型后依然可以进行实时调控。     

Study on the anisotropic photonic band gaps in three-dimensional tunable photonic crystals containing the epsilon-negative materials and uniaxial materials

In this paper, the properties of anisotropic photonic band gaps (PBGs) for three-dimensional (3D) photonic crystals (PCs) composed of the anisotropic positive-index materials (the uniaxial materials) and the epsilon-negative (ENG) materials with body-centered-cubic (bcc) lattices are theoretically studied by a modified plane wave expansion (PWE) method, which are the uniaxial materials spheres inserted in the epsilon-negative materials background. The anisotropic photonic band gaps (PBGs) and one flatbands region can be achieved in first irreducible Brillouin zone. The influences of the ordinary-refractive index, extraordinary-refractive index, filling factor, the electronic plasma frequency, the dielectric constant of ENG materials and the damping factor on the properties of anisotropic PBGs for such 3D PCs are studied in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in such 3D PCs with bcc lattices composed of the ENG materials and uniaxial materials, and the complete PBGs can be obtained compared to the conventional 3D PCs containing the isotropic materials. The calculated results also show that the anisotropic PBGs can be manipulated by the parameters as mentioned above except for the damping factor. Introducing the uniaxial materials into 3D PCs containing the ENG materials can obtain the larger complete PBGs as such 3D PCs with high symmetry, and also provides a way to design the tunable devices.     

Surface plasmon resonance-induced tunable polarization filters based on nanoscale gold film-coated photonic crystal fibers

Surface plasmon resonance induced tunable polarization filters based on nanoscale gold film-coated photonic crystal fibers were proposed and analyzed. The characteristics of the polarization filter were calculated by finite element method(FEM). The gold film was selectively coated on the inner wall of one cladding air hole which was located near the fiber core along the y-axis direction. When the phase of core fundamental mode and surface plasmon polaritons(SPPs) mode matches,the two modes couple with each other intensely. Numerical results show that the resonance wavelength and strength vary with fiber structural parameters and the index of the infilling liquid. The fiber parameters were optimized to achieve specific functions. Under the optimal structure, we realized a dual channel filter at the communication wavelength of 1.31 μm and1.55 μm for y polarization direction and x polarization direction. Then a single channel polarized filter at the communication wavelength of 1.55 μm is also achieved by adjusting the refractive index of the infilling liquid. The proposed polarization filters realized dual channel filtering and single channel filtering simultaneously under the same structure for the first time to the best of our knowledge.     

Optical filter based on omnidirectional reflectors

Optical filters based on dielectric omnidirectional reflectors are theoretically analyzed both in the frequency domain and in time domain. It is shown that an optical filter can be made by drilling periodic air holes in a dielectric omnidirectional reflector. The filter’s optical properties can be controlled by varying the lattice constant and the radius of air holes without changing the reflector’s thickness. Thus different filters can be easily integrated in one reflector. This kind of filter is expected to be used in optical communication devices and vertical cavity surface emitting lasers. PACS 42.70.Qs; 42.79.Ci; 78.20.Bh     

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.     

Quality evaluation of tunable microwave filters on ferroelectric capacitors

The tuning efficiency of microstrip filters that use ferroelectric capacitors as control elements depends on the properties of the capacitors and the filter’s resonators. The properties of these components are included if the quality criterion of a tunable filter is defined as the ratio of the center frequency tuning bandwidth to the passband of the filter. A quality criterion suggested in this work allows one to estimate the limiting characteristics of tunable filters.     

Broadband 3D isotropic negative-index metamaterial based on fishnet structure

In this paper, we numerically demonstrate a broadband 3D isotropic negative index metamaterial (NIM) at microwave frequency ranges, which is composed of double periodic array metallic fishnet structure (FS) etched on the six sides of a cubic dielectric substrate. The electric and magnetic L-C resonance circuit models are constructed to demonstrate the broadband resonance properties of the proposed 3D metamaterial. The finite integration technology (FIT) simulation and standard S parameters retrieval methods are used to calculate and analyze the negative characteristics, isotropy and polarization of the 3D model. The numerical results show that the negative index bandwidth is about 7 GHz and relative bandwidth can be up nearly to 63%, the negative-index pass band is independent of the polarization of incident waves and is almost the same for different oblique incident angles. Thus, the proposed metamaterial is good candidate as a broad-band 3D isotropic NIMs.