Theoretical modelling of one dimensional photonic crystal based optical demultiplexer

An optical demultiplexer through one-dimensional Si–SiO₂ photonic crystal structure in the presence of air cavity with a single crystal PMN-0.38PT material is presented. The transmittance of this structure is obtained using the transfer matrix method. The transmittance of this structure shows a sharp passband in the band gap region. It is observed that by introducing PMN-0.38PT layer in both sides of the air cavity, the existing band gap region of Si–SiO₂ structure is slightly increased. Here, PMN-0.38PT material is working as a tunable element for passband. By applying some external potential on PMN-0.38PT crystal, the thickness of cavity layer can be tuned and the passband can be placed at any desired wavelength in the band gap region. Since the photonic band gap region contains a range of wavelengths which are not allowed to pass through the structure can be considered as a multiplex signal for the proposed demultiplexer. Therefore, any optical signal that lies in the band gap region of the structure can be separated into its components as a pass band. Hence, the proposed structure will work as an optical demultiplexer.     

Lowpass filters with near‐maximally flat passband

Abstract

A new class of low‐pass filters, referred to as Near‐Maximally Flat (NMF) filters, with a zero passband loss at the origin and some fixed frequency near the passband edge are investigated. The magnitude response exhibits one controllable ripple in the passband and provides more stopband attentuation than the classical Butterworth filters and monotonic response class L filters. A systematic procedure is also presented to generate normalized near‐maximally flat filters with pairs of finite transmission zeros in the filter function.     

Adaptive deblurring of noisy images

We propose a practical sensor deblurring filtering method for images that are contaminated with noise. A sensor blurring function is usually modeled via a Gaussian-like function having a bell shape. The straightforward inverse function results in the magnification of noise at high frequencies. To address this issue, we apply a special spectral window to the inverse blurring function. This special window is called the power window, which is a Fourier-based smoothing window that preserves most of the spatial frequency components in the passband and attenuates quickly at the transition band. The power window is differentiable at the transition point, which gives a desired smooth property and limits the ripple effect. Utilizing the properties of the power window, we design the deblurring filter adaptively by estimating the energy of the signal and the noise of the image to determine the passband and the transition band of the filter. The deblurring filter design criteria are (a) the filter magnitude is less than 1 at the frequencies where the noise is stronger than the desired signal (the transition band), and (b) the filter magnitude is greater than 1 at the other frequencies (the passband). Therefore the adaptively designed deblurring filter is able to deblur the image by a desired amount based on the estimated or known blurring function while suppressing the noise in the output image. The deblurring filter performance is demonstrated by a human perception experiment in which 10 observers are to identify 12 military targets with 12 aspect angles. The results of comparing target identification probabilities with blurred and deblurred images and adding two levels of noise to blurred and deblurred noisy images are reported.     

An HTS 20-Pole Microstrip Filter for GSM-1800 Base Stations

In order to resolve the problems that the Chinese mobile communication was facing (high dropped call rate, not so good voice quality, etc.), we developed a 20-pole high-temperature superconductor thin-film microstrip filter with steep band edges. This filter which had a quasi-elliptic type frequency response was designed for GSM-1800 base station receiver system. Its frequency ranged from 1711 MHz to 1789 MHz. It was fabricated using double-sided YBCO thin films on LaAlO₃ substrate. The substrate size was 0.52 mm × 21 mm × 40 mm. Experiments were performed on a Stirling cooler at a temperature of 60 K. The measured insertion loss in the passband is below 0.35 dB, return loss is bigger than 13.5 dB, and the steepness of the band-edge is up to 18 dB/MHz. Then we assembled it with an LNA (low noise amplifier) into a vacuum chamber to get a base station receiver front end and measured it. Its measured gain is 22.5 dB, and noise figure is below 0.6 dB in the passband which is very important to improve the sensitivity of the base station system.     

1.5-GHz high-T c superconducting microstrip bandpass filter of miniaturized configuration

A 1.5-GHz four-stage microstrip bandpass filter was designed with the miniaturized hairpin resonator structure to reduce the configuration in size. The filter was fabricated using high-T _c superconducting films on a 12 × 12 mm² LaAlO₃ substrate. The passband insertion loss of the filter was measured to be -0.4 dB at 77 K, while it was estimated by a planar electromagnetic simulator to around -19 dB when gold films are used instead of the superconducting films.     

Design of monoblock dielectric filter using (PbCa)(FeNbSn)O3 ceramics

The microwave dielectric properties of (Pb_1-xCa_x){(Fe_0.5Nb_0.5)_1-ySn_y}O₃ ceramics (0.4 x 0.6, y = 0.05, 0.1) and design of 900 MHz band 2-pole monoblock band pass filter (BPF) have been investigated to fabricate BPF. Single-phase specimens having orthorhombic perovskite structure similar to CaTiO₃ could be obtained in the compositions of Pb_1-xCa_x){(Fe_0.5Nb_0.5)_1-ySn_y}O₃ (0.4 x 0.6, y = 0.05, 0.1). The substitution of Sn for Fe_0.5Nb_0.5) significantly increased the quality factor Q and slightly decreased the dielectric constant (_r). The temperature coefficient of the resonant frequency of 0 ppm °C^–1 was realized at x = 0.55 and y = 0.1. The Q · f ₀ value and (_r) for this composition were found to be 8600 GHz and 86, respectively. A monoblock /4 dielectric BPF for 900 MHz band portable telephone terminal is presented. This BPF is a kind of combline filter. Computer-aided design (CAD) was used in the modeling procedure. The equivalent circuit of the monoblock BPF is represented by transmission lines and lumped elements based on Z_oe and Z_oo. A BPF model was designed for surface mounted device (SMD) types. The simulations of the equivalent circuit and BPF structure have been performed to optimize the filter design. Newly developed Pb_0.45Ca_0.55){(Fe_0.5Nb_0.5)_0.9Sn_0.1}O₃ dielectric materials were used for BPF fabrication. Experimental results of the fabricated device were in good agreement with the simulation.     

基于EBG结构的基片集成波导超宽带带通滤波器

为拓展带通滤波器的通带带宽,设计了一种基于EBG结构的基片集成波导（SIW）超宽带带通滤波器．该滤波器利用箭头形电磁带隙结构的阻波特性,将不同大小箭头形结构单元蚀刻在SIW上金属面,以获得超宽带通带．所设计的滤波器中心频率在985 GHz,相对带宽为3959%,通带内的最大插入损耗约为154 dB,相比于类似结构的带通滤波器,其带内回波损耗较大,且整体电路面积较小．测量结果与仿真结果基本吻合,有效地验证了该设计方法的有效性．     

Band-pass microstripe filters using high-temperature superconducting films

Results are presented of a simulation and experimental investigation of band-pass filters consisting of coupled microstripe resonators fabricated using high-temperature superconducting films. It was shown that by using reliable models of high-temperature superconducting filter elements and careful design, it is possible to synthesize high-temperature superconducting filters as an integrated circuit without using additional tuning elements. Two filter configurations were investigated at a frequency of 1.75 GHz with a 4% pass band. A significant result is that the calculated and experimental characteristics of both filter configurations show very satisfactory agreement. Pis’ma Zh. Tekh. Fiz. 24, 50–54 (December 26, 1998)     

High-performance multilayer WSe2 p-type field effect transistors with Pd contacts for circuit applications

WSe₂ is thought to be one of the best emerging p-type transition metal dichalcogenide (TMD) materials for potential low-power complementary metal oxide semiconductor (CMOS) circuit applications. However, the contact barrier and the interface quality hinder the performance of p-type field effect transistors (FETs) with WSe₂ films. In this work, metals with different work functions—Pd, Pt, and Ag—were systematically investigated as contacts for WSe₂ to decrease the contact resistances at source/drain electrodes and potentially improve transistor performance. Optimized p-type multilayer WSe₂ FETs with Pd contacts were successfully fabricated, and excellent electrical characteristics were obtained: a hole mobility of 36 cm²V^?1 s^?1; a high on/off ratio, over 10⁶; and a record low sub-threshold swing, SS?=?95 mV/dec, which may be attributed to the small Schottky barrier height of 295 meV between Pd and WSe₂, and strong Fermi-level pinning near the top of the valence band at the interface. Finally, a full-functional CMOS inverter was also demonstrated, consisting of a p-type WSe₂ FET together with a normal n-type MoS₂ FET. This confirmed the potential of TMD FETs in future low-power CMOS digital circuit applications.

     

发动机检测仪检定装置的示波灵敏度检定设计

本文介绍了发动机检测仪检定装置的示波灵敏度电路设计。该电路由锁相环芯片CD4 0 4 6、十进制计数器CD4 5 18、低通滤波器MAX2 93和一些电阻、电容构成。电路设计合理 ,实际使用效果好     

Design of a lithium niobate Fabry-Perot étalon-based spectrometer

The design of a tunable Fabry-Perot étalon-based filter that has a passband of 0.01 nm and a free spectral band larger than 50 nm when operated in the center of the visible spectrum is described. The filter consists of two Y-cut lithium niobate étalons having thicknesses in a vernier ratio. The polarization state of light passing through the tandem étalons is rotated 90 degrees before again being transmitted through the étalon pair. If the components are arranged in a symmetrical manner, the filter will operate with unpolarized incident light. Each étalon in double pass will have a greater transmittance than two individual étalons of the same average optical thicknesses, since variations in the physical thickness due to fabrication errors are correlated.     

On realization of modified maximally flat group delay low‐pass filters

Abstract

This paper presents four tables of element values for designing maximally flat group delay low‐pass filters with Chebyshev attenuation in stopband and flat attenuation in passband.     

一种基于SIFW的小型化宽带带通滤波器

为实现射频系统的小型化,本文设计出一种基于基片集成折叠波导( Substrate integrated folded waveguide,简称SIFW)的小型化宽带带通滤波器,并给出了仿真结果.为了改善带外抑制,滤波器通过交叉耦合,在通带低端引入两个传输零点.为改善通带高端滤波特性,在顶层和底层金属微带上刻蚀互补型开口谐振环(Complementary Split Ring Resonators,简称CSRR).仿真结果表明,所实现的滤波器中心频率在7.1 GHz,相对带宽约为47％,通带内回波损耗优于-15dB,插入损耗小于0.7dB.     

Cesium Lead Inorganic Solar Cell with Efficiency beyond 18% via Reduced Charge Recombination

Cesium‐based inorganic perovskite solar cells (PSCs) are promising due to their potential for improving device stability. However, the power conversion efficiency of the inorganic PSCs is still low compared with the hybrid PSCs due to the large open‐circuit voltage (V_OC) loss possibly caused by charge recombination. The use of an insulated shunt‐blocking layer lithium fluoride on electron transport layer SnO₂ for better energy level alignment with the conduction band minimum of the CsPbI_3‐xBr_x and also for interface defect passivation is reported. In addition, by incorporating lead chloride in CsPbI_3‐xBr_x precursor, the perovskite film crystallinity is significantly enhanced and the charge recombination in perovksite is suppressed. As a result, optimized CsPbI_3‐xBr_x PSCs with a band gap of 1.77 eV exhibit excellent performance with the best V_OC as high as 1.25 V and an efficiency of 18.64%. Meanwhile, a high photostability with a less than 6% efficiency drop is achieved for CsPbI_3‐xBr_x PSCs under continuous 1 sun equivalent illumination over 1000 h.     

Narrow line-width filters based on rugate structure and antireflection coating

Filters that have high transmittance over the passband region of the reflectance spectrum are designed by combining rugate structures and antireflection (AR) coatings. It is found that, under certain conditions, the refractive index of the substrate could be “converted” to the air-side refractive index of the graded-refractive-index coating. A method for the fabrication of graded-index coatings by rapidly alternating deposition of low (SiO₂) and high (Nb₂O₅) refractive index materials is introduced, and this technology was used to fabricate a rugate structure. An AR coating with a refractive index of 1.23 was grown onto the rugate structure by glancing angle deposition technology. Optical measurements of the combined structure show excellent transmittances over the wavelength regions around the reflection band and high reflectances in the stopband.     

Widely tunable optical bandpass filter by use of polymer long-period waveguide gratings

We report the design and fabrication of a widely tunable optical bandpass filter based on using two identical long-period gratings formed along a polymer channel waveguide with a section of the waveguide core removed. The peak transmission of the passband of the fabricated filter is approximately 60% and the bandwidth of the passband is approximately 6 nm. The filter is thermally tunable over the C + L band (1520-1610 nm) for both TE and TM polarizations with a temperature control of approximately 30 degrees C.     

Band-notched ultra-wideband bandpass filter design using combined modified quarter-wavelength tri-section stepped-impedance resonator

This study presents a new band-notched ultra-wideband (UWB) bandpass filter (BPF) that is designed using a new structure-shared multi-mode resonator (MMR). The MMR is formed by combining two quarter-wavelength (λ/4) tri-section stepped-impedance resonators (TSSIRs) in a proper fashion to exhibit both λ/4 and half-wavelength (λ/2) types of resonance. With the first two resonant frequencies of the inherent λ/4 TSSIR, the first two of the parasitic λ/2 SIR and the coupling peaks of the input/output interdigital parallel-coupled lines properly located in the UWB passband, a six-transmission-pole UWB BPF can be realised. In this filter design, besides obtaining a uniform in-band transmission response, a notched band centred around 5.5 GHz is created by embedding L-shaped open-end slots in the TSSIR and loading the TSSIR with closely coupled winding-type resonators (WTRs) to filter out the 5-GHz wireless local-area network radio signal interferences. In addition, spur-lines are embedded in the TSSIR to sharpen the passband skirts for selectivity improvement.     

Superconducting Bands Stabilizing Superconductivity in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript> and MgB<Subscript>2</Subscript>

It is shown that the ceramic superconductor YBa₂Cu₃O₇ as well as the superconducting intermetallic compound MgB₂ possesses a narrow, partly filled “superconducting band” with Wannier functions of special symmetry in their band structures. This result corroborates previous observations about the band structures of numerous superconductors and non-superconductors showing that evidently superconductivity is always connected with such superconducting bands. These findings are interpreted in the framework of a nonadiabatic extension of the Heisenberg model. Within this new group-theoretical model of correlated systems, Cooper pairs are stabilized by a nonadiabatic mechanism of constraining forces effective in narrow superconducting bands. The formation of Cooper pairs in a superconducting band is mediated by the energetically lowest boson excitations in the considered material that carry the crystal-spin angular momentum 1⋅ℏ. These crystal-spin-1 bosons are proposed to determine whether the material is a conventional low-T _c or a high-T _c superconductor. This interpretation provides the electron–phonon mechanism that enters the BCS theory in conventional superconductors.     

Multilayer bandstop filter for ultra wideband systems

A multilayer broadside-coupled microstrip-slot-microstrip structure is used to design a bandstop filter with a wide passband for ultra wideband (UWB) applications. The design procedure for the proposed filter is based on the conformal mapping technique and the even- and odd-mode analysis. The theoretical analysis indicates that value of the coupling factor between the top and bottom layers of the structure can be used to control the width of the stopband, whereas centre of that band can be controlled by the length of the coupled structure. To limit the passband of the proposed bandstop filter to 3.1 ?10.6 GHz, which is the specified bandwidth for UWB systems, a broadside-coupled bandpass filter is integrated with the proposed device. The simulated and measured results show that the proposed device achieve ,0.5 dB insertion loss across most of the passband and .20 dB insertion loss at the stopband. The device also shows a flat group delay across the passband with ,0.15 ns peak-to-peak variation. Hence, it is a suitable choice for the UWB systems that require a distortionless operation.     

A digital filter chip for ECG signal processing

A VLSI implementation of a linear-phase digital filter for ECG signal processing has been designed. With a sampling rate of 100 Hz, the passband is from 0.5 Hz to 49.5 Hz with 0.5-dB ripple. The filter architecture is based on the use of recursive running-sum blocks, resulting in a very low computational complexity. Module generators have been used in the layout design for high integration density. The circuit has been designed for a 2.0-μm double-metal CMOS technology, having about 34000 transistors and a 15.43-mm² chip area