Microstrip photonic crystals used for measuring parameters of liquids

Computer simulation and experimental study of the frequency dependences of the transmission and reflection coefficients of photonic crystals based on a microstrip structure are carried out in the case when the periodicity of the structure is violated by a change in the permittivity of the substrate of one of the alternating segments of the microstrip line. A method is developed for measuring parameters of the material playing the role of inhomogeneity in the open microwave photonic structure. The complex permittivity is determined for a number of polar and nonpolar liquids.     

含超导材料Cantor序列一维光子晶体的传输特性

利用传输矩阵法研究了按分形三分Cantor序列构成的一维超导光子晶体的传输特性。数值结果表明,与传统电介质材料构成的光子晶体的频谱不同,这种光子晶体频谱没有展现出自相似性。此外,当构成光子晶体的两种材料的光学厚度相同时,光子晶体的频谱具有明显的周期性,并且在光子带隙中间成对地出现缺陷模。这种特性可以用于设计通道滤波器。     

Coefficient of ultrasound transmission from liquid helium to aluminum in the intermediate state at <Emphasis Type="Italic">T</Emphasis> ≈ 0.1 K

The coefficient α(θ) of ultrasound transmission from liquid ⁴He to an aluminum single crystal in intermediate, superconducting, and normal states at a temperature T ≈ 0.1 K is measured as a function of the polar angle θ at the azimuthal angle φ = 0. The experimental technique is based on the measurement of the Kapitza temperature jump at the interface between two media. The dependences of the transmission coefficient for the Rayleigh modes on the sound frequency (in the range 13–194 MHz) and the magnetic field strength are determined. It is demonstrated that the integrated transmission coefficient of the aluminum single crystal in the intermediate state at an angle θ_R larger than the critical value increases with an increase in the magnetic field strength. The integrals of the transmission coefficient in magnetic fields close to the field H _c are independent of the frequency. In the vicinity of H = 0, the transmission coefficient at ν > 39 MHz increases only slightly with increasing frequency. At the lowest frequencies, the transmission coefficient increases anomalously as the frequency decreases. The experimental data are compared with the results obtained in the framework of the Andreev theory. Numerical calculations are performed and the dependences α(θ, φ) for bulk modes in the range corresponding to angles smaller than the critical value are constructed for the three principal planes of the crystal, i.e., the (001), (011), and (111) planes. The dependence α(θ) is obtained for the azimuthal angle φ = 0. The width of the Rayleigh peak is estimated.     

Parameters of defect mode of 1D microwave waveguide photonic crystal with metal inclusions in the element that disturbs periodicity

Amplitude–frequency characteristics of the transmission coefficient of microwave waveguide photonic crystal with violation of periodicity are studied in the presence of a plane conducting small-size inclusion that occupies a part of the transverse cross section of the waveguide inside a disturbed layer located at different positions. The conducting small-size inclusion in the disturbed layer of photonic crystal causes the low-frequency shift of the defect mode in the band gap, and the maximum shift is observed when the metal inclusion is located at the interface or center of disturbance depending on the thickness of the disturbed layer.     

Adiabatic coupling between conventional dielectric waveguides and waveguides with discrete translational symmetry

We study adiabatic transformation in optical waveguides with discrete translational symmetry. We calculate the reflection and transmission coefficient for a structure consisting of a slab waveguide that is adiabatically transformed into a photonic crystal waveguide and then back into a slab waveguide. The calculation yields high transmission over a wide frequency range of the photonic crystal waveguide band and indicates efficient coupling between the slab waveguide and the photonic crystal waveguide. Other applications of adiabatic mode transformation in photonic crystal waveguides and the coupled-resonator optical waveguides are also discussed.     

Photonic crystals for the visible spectrum by holographic lithography

We describe a general and flexible technique for the fabrication of three-dimensional photonic crystals that is particularly well adapted to the production of structures with the sub-micron periodicity required for applications in the visible optical spectrum. Three-dimensional microstructure is generated by using a four-beam laser interference pattern to expose a thick layer of photoresist. Exposed areas are rendered insoluble; unexposed areas are dissolved away leaving a three-dimensional photonic crystal formed of cross-linked polymer with air-filled voids. The polymeric structure may be used as a template for the production of photonic crystals with higher refractive index contrast. Photonic crystals made of polymer and of TiO₂ have been characterized by scanning electron microscopy and by optical diffraction measurements.     

Low group velocity in a photonic crystal coupled-cavity waveguide

A two-dimensional photonic crystal coupled-cavity waveguide is designed and optimized, the transmission spectrum is calculated by using the finite-difference time-domain method, and the group velocity of c/1856 is obtained. To our knowledge, this value of group velocity is the lowest group velocity in a photonic crystal waveguide calculated from its transmission spectrum so far. The result is confirmed by the photonic band structure calculated by using the plane wave expansion method, and it is found that the photonic crystal waveguide modes in a photonic band structure are in accordance with those in the transmission spectrum by using the finite-difference time-domain method. The mechanism of slow light in the coupled-cavity waveguide of photonic crystal is analysed.     

A comparative study of dispersion relation of EM waves in ternary one-dimensional plasma photonic crystals having two different structures

In this paper, a rigorous theoretical analysis has been made to study the dispersion relation of EM waves in periodic ternary one-dimensional photonic crystal having two different structures. In one case we have chosen glass-plasma and ZnS in one unit cell and in other case we have considered glass-plasma and M_gF₂ in one unit cell. Using Kronig-Penney model the dispersion relation for proposed structures has been obtained and numerical results are presented in the form of dispersion curves. The dependence of photonic band gap (PBG) characteristics on plasma frequency, plasma width and the width of dielectric media are discussed in the light of frequency gap and cutoffs of binary one-dimensional plasma photonic crystal. An attempt has been made to show how the PBG characteristic of a particular structure changes when the dielectric materials of its unit cell is changed by the other dielectric material. It is found that the structure having glass-plasma-ZnS in unit cell is more useful for broad band filtering and other plasma functioning devices compared to the structure having glass-plasma-MgF₂ in one unit cell.     

用传输矩阵法研究微波波段准一维同轴光子晶体能隙结构

用SMA型同轴标准接头组成具有准一维晶格结构的光子晶体，测试结果表明具有明显的光子带隙结构.利用传输线等效模型和布洛赫周期性边界条件模拟分析也表明同轴准一维光子晶体具有能隙结构，理论计算结果与实验结果能很好吻合. 关键词： 光子晶体 同轴 能隙结构 传输矩阵     

Numerical analysis of the As2Se3 chalcogenide glass multi-ring photonic crystal fiber

A novel kind of As₂Se₃ chalcogenide glass multi-ring photonic crystal fiber is proposed. The characteristics of multi-ring photonic crystal fiber have been studied by the finite element method. Compared with another two kinds of single-core photonic crystal fibers, the multi-ring PCF can make the perfect combination of the effective mode area, the nonlinearity coefficient and multi-zero dispersion. It can achieve high power supercontinuum generation in middle infrared band; It also can be used in high-power pulsed laser fiber amplifier and high-power ultra-short pulse laser transmission in far infrared band.     

Ge20Sb15Se65硫系玻璃光子晶体光纤的中红外色散特性

硫系玻璃与石英玻璃相比具有高折射率(2.0~3.5)、低声子能量 (<350 cm^-1)、优良的中远红外透过性能(可至25 μm)等特性.本文制备了一种在中红外具有优良透过特性的无As环保型Ge₂₀Sb₁₅Se₆₅硫系玻璃材料,以此为基质材料设计了一种三层空气孔结构光子晶体光纤,利用多极法对光纤的中红外色散特性进行了数值模拟,系统研究了结构参量孔径d、孔间距Λ 以及d/Λ 对其色散特性的影响.分析表明:通过改变包层空气孔直径d或空气孔间距Λ,可灵活的调节光子晶体光纤的零色散波长向短波或长波方向移动.通过优化结构参量发现,当Λ=3 μm,d/Λ=0.35 附近变化时,可获得3~5 μm色散平坦,且色散值小于5 ps·nm^-1·km^-1的光子晶体光纤.     

1×4光子晶体波导分束器的特性

在完整的二维光子晶体中引入线缺陷,形成了光子晶体波导,光子晶体波导分束器是集成化光学电路的重要组成元件。我们设计了一种线缺陷1×4光子晶体分束器,并且用有限时域差分法研究了它的特性。研究表明,输出端的透射传输特性与入射光的波长和分支的几何形状有关,并且入射波分别相等地流入四个输出端口。为了减少1×4分束器在三个Y型分支区的反射,可以通过调节在分支区的可调介质柱的半径R,使每个输出端口具有很高的透射率。     

三种典型结构光子晶体光纤基本特性的比较和分析

应用多极法比较和分析了相同结构参数下的正六边形、正八边形和正十边形光子晶体光纤的色散系数、色散斜率、非线性系数和限制损耗.正六边形光子晶体光纤更适合用于色散补偿和高非线性的研究,在波长0.8 μm处的非线性系数达到了0.37 m^-1·W^-1;正十边形光子晶体光纤更适合用于色散平坦和低限制损耗的研究,在波长0.8 μm处的限制损耗相对正六边形光子晶体光纤减小了约3000个数量级,在1.4—1.65 μm波长范围内,正十边形光纤的色散系数介于-0.07—0.17 p     

Effective dielectric constant of two-dimensional photonic crystals in optical bands

By using the Fourier expansion method, we have developed an approach to calculate the effective dielectric index of a two-dimensional photonic crystal. The approach is very general: it can take into account various Bravais lattice structure as well as arbitrary spatial variation of the dielectric index. It has been found that near a nondegenerate frequency ω_n(Γ) at Γ point, the transverse magnetic (TM) mode is ordinary, as it is independent of the propagation direction, whereas in general the transverse electric (TE) mode depends on the propagation direction, it is extraordinary. Therefore, a two-dimensional photonic crystal can always be described by an effective dielectric index for TM mode near the nondegenerate frequency ω_n(Γ). However, the TE mode is much more complicated unless the lattice structure is highly symmetric. Moreover, a two-dimensional square photonic crystal has been identified as an effective birefringent crystal having two negative refractive indexes from the perspective of Snell's law.     

Dielectric photonic crystal with a near-zero effective refractive index in the microwave range

The microwave propagation in a 3D dielectric photonic crystal at the frequency range from 8.5 to 12GHz has been investigated. A frequency range where effective refractive index n _ef of the crystal approaches zero is found. In the frequency range where n _ef <0.2, themicrowave beam becomes collimated, sharpened, and free of diffraction noise. An excitation of a surface wave, propagating along the external surface of the structure, is revealed in same frequency range. This property of the photonic crystal structure can be used to screen and mask objects scanned by external radiation.     

Modelling of 3D photonic crystals based on opals

The construction of 3D photonic crystals with gaps in the visible or the near-infrared frequency range requires engineering of complex microstructures which are very difficult to realize by etching and micro-fabrication. Consequently, self-ordered systems such as synthetic opals are very promising. Synthetic bare opals are constituted by SiO₂ spheres that organize themselves by a sedimentation process in a face centered cubic (fcc) arrangement. Using the plane wave method, we examine the photonic band structures of close-packed opal-based photonic crystals with an SiO₂ (n = 1.5) matrix. The incomplete photonic band gaps at the X- and L-points have been studied which correspond to normally incident plane waves onto the (100) and (111) crystal planes. With the transfer matrix method, we model the transmission properties. We find that the incomplete gap at the L-point fully inhibits the transmission of waves propagating in the [111] direction for opal sample thicknesses that are easily obtainable. This property shows that bare opals could be good candidates for complete inhibition of transmission in the near-infrared and visible frequency range for given orientations.     

Control of absorption spectrum of a one-dimensional resonant photonic crystal

The crystal under consideration is a layered structure consisting of alternating layers of two materials, one of which is a resonantly absorbing gas. It is shown that the combination of the dispersion of an atomic gas with the dispersion of a photonic-bandgap structures allows one to efficiently control the transmission spectra of s- and p-polarized modes in these combined systems. It is found that the spectrum is highly sensitive to the position of the gas resonance frequency with respect to the bandgap edge and to a change in the gas pressure. The transmission, reflection, and absorption spectra of the resonant photonic crystal are studied at an angle of incidence equal to the Brewster angle of a seed photonic crystal. Possible applications of the found particular features of the dispersion of resonant photonic crystals are discussed.     

Angular tuning of defect modes spectrum in the one-dimensional photonic crystal with liquid-crystal layer

A one-dimensional ZrO₂/SiO₂ photonic crystal with a 4-n -pentyl-4' -cyanobiphenyl (5CB) nematic defect layer was used to investigate the transmission spectra of light polarized parallel and perpendicular to the liquid-crystal director at different angles of incidence. The spectra of the photonic crystal were shown to split into four polarized components T_ij at oblique incidence. When the incident angle increased, the bandgap edges and the defect modes shifted towards short wavelengths, while the amplitudes of the defect modes increased for the transverse magnetic polarization and decreased for the transverse electric polarization. The observed discrepancy between the defect mode amplitudes in the center and near the edges of the photonic bandgap was found to be related to the radiation losses inside the defect layer of a non-ideal photonic crystal. The simulated transmission spectra obtained using recurrence relations and taking into account the decay of defect modes are in good agreement with the experimental data.     

Microfabrication and Characteristics of Two-Dimensional Photonic Crystal Structures in Vitreous Silica

We report for the first time a laser microfabrication and its characteristics of photonic crystal structure in vitreous silica. It is two-dimensional triangle lattices composed of hollow cylinders with a periodicity of approximately 1.2 μm. Infrared spectroscopic measurements revealed dielectric-periodicity-matched transmission valleys centering approximately at 4100 cm⁻¹ for H-polarization and 4000 cm⁻¹ for Epolarization, respectively.     

由单负材料组成的含有缺陷层的一维光子晶体结构中的缺陷模

用转移矩阵方法研究了由单负材料组成的含有缺陷层的一维光子晶体的透射特性.研究结果表明:当缺陷层存在时,会在原有光子晶体的禁带中出现缺陷模.缺陷模的位置随杂质层磁导率μ的增加从禁带的高频端向低频端移动;但随杂质层介电常数ε的增加却从禁带的低频端向高频端移动.利用该特性可以实现对光传播的动态调控. 关键词： 单负材料 光子晶体 缺陷模