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.     

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.     

含负折射率材料1维光子晶体的偏振无关非全向的缺陷模

运用光学传输矩阵理论,研究了含负折射率材料1维光子晶体缺陷模的偏振特性。结果显示,零均折射率带隙中缺陷模对入射角和偏振有较强的依赖。通过对缺陷层参数的优化设计,得到了一系列的偏振无关非全向缺陷模,这是传统1维光子晶体中不能出现的。应用这些缺陷模,设计了低通、高通、带通空间滤波器。与传统光子晶体空间滤波器相比,这些空间滤波器具有偏振无关的优点。     

含负折射率材料1维光子晶体的偏振无关非全向的缺陷模

运用光学传输矩阵理论,研究了含负折射率材料1维光子晶体缺陷模的偏振特性。结果显示,零均折射率带隙中缺陷模对入射角和偏振有较强的依赖。通过对缺陷层参数的优化设计,得到了一系列的偏振无关非全向缺陷模,这是传统1维光子晶体中不能出现的。应用这些缺陷模,设计了低通、高通、带通空间滤波器。与传统光子晶体空间滤波器相比,这些空间滤波器具有偏振无关的优点。     

Very-large-mode-area photonic bandgap Bragg fiber polarizing in a wide spectral range

A design of a polarizing all-glass Bragg fiber with a microstructure core has been proposed for the first time. This design provides suppression of high-order modes and of one of the polarization states of the fundamental mode. The polarizing fiber was fabricated by a new, simple method based on a combination of the modified chemical vapor deposition (MCVD) process and the rod-in-tube technique. The mode field area has been found to be about 870 μm2 near λ=1064 nm. The polarization extinction ratio better than 13 dB has been observed over a 33% wavelength range (from 1 to 1.4 μm) after propagation in a 1.7 m fiber piece bent to a radius of 70 cm.     

Properties of defect modes in one-dimensional photonic crystals containing a graded defect layer

The properties of defect modes in one-dimensional photonic crystals (PCs) containing a graded defect layer are studied theoretically. The relative permittivity and magnetic permeability of the graded defect layer vary continuously along the direction perpendicular to the surface of the layer. The effect of the linear gradation profiles of the relative permittivity and permeability are studied in detail. It is shown that the defect modes appear inside the forbidden band gaps in its transmission spectra and the gradation profiles of the relative permittivity and permeability affect the defect modes significantly. By changing the gradation parameters, the intensity and position of the defect modes can be tuned. Therefore, introducing a graded defect layer in one-dimensional PCs provides possible mechanism for tuning the defect modes. This may be useful in the design of channeled filters.     

Robust wide zero-average-index gap in photonic heterostructures that incorporate left-handed materials

In this article, we theoretically study electromagnetic waves that propagate in a one-dimensional photonic heterostructure that contains left-handed materials. We suggest a type of heterostructure that is composed of two photonic crystals (PCs) that consist of different materials, rather than the previously studied heterostructures that are based on changing the thicknesses of alternating layers, to target zero-average-index gap enlargement. Numerical calculations of the transmittance show that the suggested structure possesses an ultra-wide zero-average-index gap that is robust for both transverse electric and magnetic polarizations. The demonstrated wide gap is independent of the incidence angle. The proposed structure works as a perfect stop-band filter, which completely blocks both polarizations, and may have many other potential applications.     

Complete photonic band gaps in one-dimensional ternary photonic crystals containing single negative materials

Complete photonic band gaps (PBGs) are found in one-dimensional ternary photonic crystals (1D TPCs) composed of an ordinary dielectric and single negative metamaterials. The proposed TPC gives omni directional PBG completely independent of polarizations dependent weekly on angle of incidence. Here the choice of different parameters of TPC is done in such a way so that it eliminates the Brewster's-angle transmission resonance, thus allowing a complete 3D PBG. It exhibits a photonic band or gap near frequencies where either the magnetic permeability or the electric permittivity of the metamaterial changes sign, whose width increases with the increasing angle of incidence. These result from the dispersive properties of the metamaterials and disappear for the particular case of propagation along the stratification direction. The results are discussed in terms of incident angle, layer thickness, dielectric constant of the dielectric material for TE and TM polarizations.     

Band gaps and nonlinear defect modes in one-dimensional photonic crystals with anisotropic single-negative metamaterials

We propose a one-dimensional photonic crystal (1DPC) with multilayered periodic structures containing dispersive anisotropic single-negative (ASNG) (permittivity- or permeability-negative) metamaterials. The influences of the ratio of d_A/d_B and their scale on ASNG gaps are discussed. Moreover, the effect of a nonlinear defect layer introduced into the proposed structure is also analyzed, and the results show that the defect mode has two peaks of electrical fields in the defect layer and its bistability property is also different from a defect mode in PCs with isotropic SNG gaps.     

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.     

Properties of defect modes in one-dimensional photonic crystals containing two nonlinear defects

Transmission properties of one-dimensional photonic crystal with two nonlinear defects were investigated based on the nonlinear transfer matrix method. From the inspection of the optical bistabilities around different defect modes, it was found that the threshold of bistability for the bonding mode is always lower than that for the anti-bonding mode. When intensity of the incident wave increases bistability could happen at any wavelength larger than the resonance wavelength of the linear anti-bonding mode in the gap. The threshold of bistability increases initially with the wavelength, then decreases sharply in reaching the resonance wavelength of the linear bonding mode. The coupling behavior of the two defects was also discussed, and it was found that the threshold of bistability increases with the distance between the two defects. A flat spectrum similar to that formed in the photonic crystal molecules was obtained under certain incident intensity.     

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 important for different applications.     

Time-domain investigation of the tunneling modes in photonic heterostructure containing single-negative materials

We present a theoretical investigation into the energy transport and transient wave propagation in metamaterial tunneling structures consisting of ??-negative (ENG) and ??-negative (MNG) materials. It is proved that a conjugated matched ENG/MNG bilayer and a (zero-index-material doped) photonic crystal heterostructure can work as a sub-wavelength resonator at tunneling frequency. The tunneling modes need a certain time to achieve the steady state and the charge up characteristic time increases (nearly) exponentially with the thickness of the structures. Under the steady state, the wave in the single-negative-material structures is not evanescent, but a hybrid of a traveling wave and a reactive standing wave. The phase difference between the electric field and the magnetic field varies with the position and time. The investigation of transient wave propagation in the metamaterial tunneling structures will help us to understand the interaction process between wave and metamaterial and to design special functional apparatus.     

Band gaps and defect modes in periodically structured waveguides

This work examines a simple one-dimensional acoustic band gap system made from a diameter-modulated waveguide. Experimental and theoretical results are presented on perfectly periodic waveguide arrays showing the presence of band gaps--frequency intervals in which the transmission of sound is forbidden. The introduction of defects in the perfect periodicity leads to narrow frequency transmission bands--defect states--within the forbidden band gaps. The circular cross-section waveguide system is straightforward to simulate theoretically and experimental results demonstrate good agreement with theory. The experimental transmission of the periodic waveguide arrays is measured using an impulse response technique.     

Photonic-band-gap structures and guide modes in two-dimensional magnetic photonic crystal heterostructures

We first investigate the band gap structures of two-dimensional magnetic photonic crystals (MPC) composed of rectangular (square) magnetic cylinders embedded in a host dielectric material in the rectangular (square) lattice, and we then study guide modes at interface of MPC heterostructures (MPCHs) by use of plane wave expansion method in combination with supercell technique. We find that both the mirror-symmetric MPCHs and the mixed-type MPCHs composed of square cylinders in a square lattice can produce the TM guide modes even without any lattice distortions. This feature is quite different from that of the non-magnetic PC heterostructures, in which the occurrence of the guide modes requires the relatively longitudinal gliding or transverse displacement of lattices. It may provide a new way to generate guide modes and apply to the device of light wave guides.Received: 26 August 2003, Published online: 2 April 2004PACS: 42.70.Qs Photonic bandgap materials - 78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures - 63.20.Pw Localized modes - 42.79.Gn Optical waveguides and couplers     

Investigation of defect modes in a defective photonic crystal with a semiconductor metamaterial defect

In this work, we theoretically investigate the properties of defect modes in a defective photonic crystal containing a semiconductor metamaterial defect. We consider the structure, (LH)^N/D^P/(LH)^N, where N and P are respectively the stack numbers, L is SiO₂, H is InP, and defect layer D is a semiconductor metamaterial composed of Al-doped ZnO (AZO) and ZnO. It is found that, within the photonic band gap, the number of defect modes (transmission peaks) will decrease as the defect thickness increases, in sharp contrast to the case of using usual dielectric defect. The peak height and position can be changed by the variation in the thickness of defect layer. In the angle-dependent defect mode, its position is shown to be blue-shifted as the angle of incidence increases for both TE and TM waves. The analysis of defect mode provides useful information for the design of tunable transmission filter in semiconductor optoelectronics.     

Analysis of defect mode in a dielectric photonic crystal containing ITO defect

In this work, based on the use of ITO as a defect, we study the infrared defect mode in defective photonic crystal made of SiO₂ and InP. Due to the dispersion in the dielectric function of ITO, it is found that the defect mode is sensitive to the ITO thickness. The defect frequency is shown to be blue-shifted as the thickness of ITO decreases. In the angular dependence of defect mode, it is seen that the defect frequency is also blue-shifted when the angle of incidence increases for both TE and TM polarizations. However, the shifting feature is appeared to be nearly polarization-independent. The shift in the defect frequency enables us to employ ITO as a tunable agent in order to design a tunable photonic crystal filter in the infrared region.     

Investigation on temperature characteristics of weak fiber Bragg gratings in a wide range

A weak fiber Bragg grating(WFBG) is an ideal quasi-distributed optical fiber sensor. Special attention should be paid to the spectrum and sensing performance of the WFBG at extreme temperatures due to its poor reflection intensity. In this Letter, the temperature characteristics of the WFBG from-252.75°C to 200.94°C are experimentally investigated. Five WFBGs with reflectivity from ~0.25% to ~10% are used in the experiments. The reflectivity variations and wavelength shifts at different temperatures are studied. Experimental results show that the WFBG can survive and work at extreme temperatures, but the performance is affected significantly.The reflectivity is affected significantly by both cryogenic temperature and high temperature. The temperature responses of Bragg wavelengths in the wide temperature range are also obtained.     

Enhanced second-harmonic generation for multiple wavelengths by defect modes in one-dimensional photonic crystals

We present an effective design of aperiodically stacked layers of nonlinear material and air, sandwiched by two truncated photonic crystals, in terms of the simulation annealing method. The constructed structure can achieve multiple-wavelength second-harmonic generation (SHG) at the preassigned wavelengths. We derive a general solution of SHG in 1D inhomogeneous systems and apply it to evaluate the SHG conversion efficiency. Numerical simulations show that the conversion efficiency of SHG can be significantly enhanced when the fundamental wave frequencies are assigned to the designed defect states.     

二维周期性复合介质中声波带隙结构及其缺陷态

用平面波展开方法和超元胞方法,研究了钢柱体在水中按周期性排列时声波的能带结构.讨论了钢柱体的横截面形状(圆形和正方形)、柱体的体积填充率及缺陷等因素对声波带隙结构的影响. 关键词： 声波 带隙 缺陷态