Different kinds of band-pass filters based on one-dimensional photonic crystal heterostructures

Three kinds of band-pass filters (BPFs), termed a TE BPF, a TM BPF and a BPF at oblique incidence, are designed by crossing the band edges of two different one-dimensional (1D) photonic crystals (PCs). The TE BPF, fulfilling the function of high reflectivity for p-polarization and high transmittance in a narrow pass-band for s-polarization, is constructed by two subPCs, one of which is obtained by decreasing the lattice constant of the other one while the other parameters keep the same. The TM BPF also comprises two subPCs, but the materials of one subPC are quite different with those of the other one. Similarly, the BPF at oblique incidence, from which both polarization waves can transmit in a narrow pass-band at oblique incidence, is composed of two different subPCs. Note that, the distribution of the wave impedance of material in each BPF should be periodic to prevent unexpected defect modes. The new filters not only provide narrow pass-bands and wide non-transmission bands, but also have simple structures. This is a result of the fact that the wave impedance ratio between composites is enlarged by introducing magnetic materials. The new designs have potential applications in optical filters and optical integrated circuits.     

Characteristics of microwave filters based on microstrip photonic bandgap ring structures

We study the characteristics of microstrip ring exhibiting photonic band gap properties. Since the stop band is caused by the reflection of electromagnetic waves at the narrow gap introduced in the ring, the geometry of the ring can influence on the characteristics of stop band. The center frequency of the stop band is determined mainly by the outer ring radius when the line width of the circular ring is rather narrow. But it is determined mainly by the mean ring radius when the ring is not a circular form or the line width of circular ring is wide. The frequency range of the stop band can be varied by a reactive component mounted on the gap. The presence of capacitor (inductor) on the gap decreases (increases) the center frequency and the frequency range of the stop band. Moreover, the stop band can be widened by modifying the geometry of ring. These properties can be useful in the applications to the compact microwave circuits, tunable filters and microwave switches.     

基于薄膜光子晶体超晶格理论的偏振带通滤波器

偏振带通滤波器在光通讯波分复用技术中有着特殊的应用.利用薄膜一维光子晶体超晶格概 念，提出了两种新的偏振带通滤波器的设计方法.第一种是基于两个一维光子晶体叠加的偏 振带通滤波器；第二种是在第一个光子晶体的中间插进第二个光子晶体，形成三个一维光子 晶体叠加的偏振带通滤波器.设计了性能优良的p偏振分量透射而s偏振分量反射的新型带通 滤波器.讨论了这种滤波器的通带特性和截止宽度. 关键词： 薄膜光子晶体 超晶格 偏振带通滤波器 波分复用系统     

低温对中波红外带通滤光片光谱特性的影响

为考察滤光片在低温环境下的可靠性,镀制了Ge基和宝石基中波带通滤光片,分别实施了5 min、15 min、25 min、35 min、120 min、300 min的液氮低温试验,并测试出其透过率曲线,考察低温对其光谱特性及膜层牢固度的影响。带通滤光片通带区透过率随低温时间增长有逐渐下降趋势,中心波长出现13 nm的微小偏移,是所镀制的膜料高、低折射率相对变化使中心波长和截止波长的比值发生变化所致。Ge基材料对温度更为敏感,在由常温到低温过渡期间,Ge基中波滤光片通带透过率降低幅度比宝石基底的中波带通滤光片大10%。在300 min以内的低温环境下,2种中波红外带通滤光片均未出现膜层脱落现象。     

Spectral-domain analysis of submillimetre-wave microstrip filters

We consider the cut-off frequencies of high-order modes in boxed submillimetre-wave microstrip filters. It is shown that many of the filters in use at the present time are not cut off in the way that the designers imagine. It is also shown that for ease of manufacture the height of the microstrip channel should be 0.7 times the width and the thickness of the quartz substrate should be 0.5 times the width. This optimum geometry suggests that the upper frequency limit of conventional waveguide components is 1THz.     

Electro-optic tunable band-stop filters using piezoelectric superlattices

A novel band-stop filter, which uses the piezoelectric superlattices with the external direct-current (DC) electric fields, is presented. The forbidden band of the band-stop filter can be generated by the coupling between lattice vibration and electromagnetic waves and can be tuned continuously and reversibly by the DC electric field via the electro-optic effect. The band structures and transmission spectra of the band-stop filter show that the relative bandwidth of forbidden bands will be increased from 0.43% to 26.2% and their sizes can be broadened from 0.043 GHz to 2.98 GHz when the DC electric field is increased from 0 to $1.343\times {10}^6$ V/m. The bandwidth tunability by the electro-optic effect provides a good guidance for the filter design that works in broadband frequencies.     

基于缺陷地结构的微带低通滤波器设计

提出了一种具有宽带带外抑制的小型化微带低通滤波器。该滤波器由缺陷地结构和两阶阶跃阻抗单元结构构成。利用ANSYS HFSS建立三维全波电磁模型并仿真优化,仿真结果表明：该低通滤波器的截止频率为1.4 GHz,通带宽度为0~1.4 GHz,通带内的插入损耗小于0.5 dB,带外抑制频率范围为2.1~11 GHz,在阻带范围内的带外抑制能力接近20 dB。为验证仿真和测试结果,加工并测试了经全波电磁优化后的缺陷地结构微带低通滤波器。测试结果和仿真结果吻合得较好,证明了所提出的缺陷地结构在实现滤波器小型化和宽阻抗带宽上有着重要的作用,能够使该滤波器具有较好的低通滤波特性。     

Modal parameter identification using the log decrement method and band-pass filters

This paper presents a time-domain technique for identifying modal parameters of test specimens based on the log-decrement method. For lightly damped multidegree-of-freedom or continuous systems, the conventional method is usually restricted to identification of fundamental-mode parameters only. Implementation of band-pass filters makes it possible for the proposed technique to extract modal information of higher modes. The method has been applied to a polymethyl methacrylate (PMMA) beam for complex modulus identification in the frequency range 10-1100 Hz. Results compare well with those obtained using the Least Squares method, and with those previously published in literature. Then the accuracy of the proposed method has been further verified by experiments performed on a QuietSteel specimen with very low damping. The method is simple and fast. It can be used for a quick estimation of the modal parameters, or as a complementary approach for validation purposes.     

Integral method of nondestructive testing of optically transparent dielectric elements of band-pass filters

The narrow and wide band-pass filters with high electrical parameters both in the centimeter and millimeter wave band developed in the Microwave laboratory are built on the basis of H- and E-plane inserts made of a high Q dielectric monocrystal leukosapphire (tg 6*10^–6 in centimeter wave band). The filters based on the E-plane inserts have a rare spectrum of parasitic modes (up to doubled working frequency and higher) and those based on the H-plane inserts have lower insertion loss in the bandwidth. Fig.1 shows the design of a band-pass filter in which the resonators of both the first and second types are used to improve stability of amplitude-frequency characteristic in response to influence of production process and climatic factors. The electrodynamic calculation of such a filter electrical parameters is carried out according to the technique analogous to the one described in [1]. The prooedure of the band-pass filter manufacture envisages the operation of determining whether a specific dielectric element fits for pasting into the filter body. The most expedient testing method for filter elements is the electromagnetic resonance method. However, since the monocrystal leukosapphire is an anisotropic, opticallytransparent material [2], there exists a possibility of using not only the traditional SHF (Super High Frequency) method but also the method of optical testing of the quality of the dielectric element by the shape of conoscopic figures that enables to increase the output of suitable products with reduction of expenditure. A new approach to the nondestructive testing of optically-transparent filter elements using both methods and their mutual dependence in technological process, has been suggested.     

直线型端口类盒型拓扑结构微带滤波器设计

针对微波带通滤波器小型化、高性能的应用需求,研究了基于双模方形环谐振器的直线型端口的两阶带通滤波器响应特性,进一步提出使用单模谐振器和双模谐振器相结合设计直线型端口的高阶微带带通滤波器。提出的直线型端口双模方形环微带滤波器具有类盒型拓扑结构,能够实现灵活的频率响应特性,而且传输零点的位置可调,能够满足不同的应用需求。由于存在寄生的对角交叉耦合路径,提出的类盒型拓扑结构微带滤波器可以实现一个额外的传输零点。为了验证结构和设计方法的可行性,设计了两款中心频率为5.2 GHz的三阶和五阶带通滤波器,最后进行加工和测试。耦合矩阵响应、仿真和测试结果一致性较好,表明了该结构实现高性能滤波器的可行性。     

Solar-blind ultraviolet band-pass filter based on metal–dielectric multilayer structures

Solar-blind ultraviolet （UV） band-pass filter has significant value in many scientific, commercial, and military appli- cations, in which the detection of weak UV signal against a strong background of solar radiation is required. In this work, a solar-blind filter is designed based on the concept of ＂transparent metal＂. The filter consisting of Al/SiO2 multilayers could exhibit a high transmission in the solar-blind wavelength region and a wide stopband extending from near-ultraviolet to infrared wavelength range. The central wavelength, bandwidth, Q factor, and rejection ratio of the passband are numerically studied as a function of individual layer thickness and multilayer period.     

LWIR detector arrays based on nipi superlattices

We propose that nipi superlattice structures in InSb or InAs can be grown with modern techniques to achieve tunable and stable LWIR detectors with high performance. We examine key device and material considerations for the application of such nipi superlattices to LWIR detectors. It is shown that practical absorption coefficients (≈ 100 cm⁻¹) can be achieved with high doping concentrations (≈ 10¹⁹ cm⁻³) achievable in these materials. In particular, recent delta doping techniques being developed in molecular beam epitaxy offer promise of higher doping concentrations, improved uniformity, and greater flexibility in tailoring the structures for optimum detector performance.     

Pulsed laser deposited superlattices based on perovskite oxides

Recent advances made in the field of pulsed laser deposited superlattices made up of perovskite oxides are reviewed. The superconducting properties and the effect of adjacent layers in ultra-thin YBCO are studied in YBCO/(Pr_xY_1−x)BCO superlattices. We describe the effects of layering in (La_0.7Ba_0.3)MnO₃for the purposes of fundamental studies and possible applications of these newly recognized colossal magnetoresistance materials.     

Add-drop filters based on mode-conversion cavities

A new type of a resonator defined by two or more mode-converting gratings in a waveguide is proposed and analyzed. It is shown that the proposed structure can exhibit narrow resonances similar to Fabry-Perot cavities but has an advantage of being a four-port device and thus is capable of serving as an add-drop filter.     

Study of a microstrip antenna on anisotropic metamaterials

The annular ring microstrip antennas on metamaterial substrates are modeled and analyzed using full-wave analysis in conjunction with Ansoft HFSS^TM. The influence of the permeability tensor of the split ring resonator medium on the resonant characteristics of the antenna is considered. Numerical results for typical resonant frequency behavior and return loss are presented as function of the metamaterial properties and antenna structural parameters.     

Nonlinear Bragg structures based on ZnS/ZnSe superlattices

Nonlinear optical response of periodic ZnSe/ZnS heterostructures is reported using interband excitation of a ZnSe sublattice by nano-, pico- and femtosecond laser pulses. A considerable shift of the reflection spectrum and large relative reflection changes were observed in a wide spectral range corresponding to the transparency region of ZnSe far from the intrinsic absorption onset. Evaluated refraction-index change is about −0.05 with the relaxation time being about 3 ps. In the case of femtosecond excitation, a wide-band nonlinear response is observed for both one-photon near-UV and two-photon near-IR excitation. The nonlinear refraction is supposed to be controlled by population-induced absorption changes in ZnSe single crystals and relevant refraction-index modification via Kramers–Kronig relations. The nonlinearity relaxation time is supposed to trace a transition from a non-equilibrium to a quasi-equilibrium distribution of electrons and holes within ZnSe conduction and valence bands, respectively, rather than the electron–hole recombination time. The nonlinearity mechanism does not reduce to just population-dependent absorption saturation, but essentially results from the specific distribution function in the first instance after excitation.