Bandwidth estimation for ultra-high-speed lithium niobate modulators

The effects of velocity matching, impedance matching, conductor loss, and dielectric loss on the optical bandwidth of an ultra-high-speed lithium niobate modulator are reported. It is shown that both dielectric loss and impedance matching play a key role for velocity-matched high-speed modulators with low conductor loss. The effects of etch depth, buffer thickness, electrode width, and thegap between the electrodes on device performance are also illustrated.     

铌酸锂光纤型行波调制器研究

以LiNbO3光纤作为通光部分,Si2N2O为衬底分别取代了传统波导电光调制器的中Ti:LiNbO3波导和铌酸锂衬底设计了带宽为95.49 GHz铌酸锂光纤型调制器.今利用有限元法分析SCPS电极结构下该铌酸锂光纤调制器的性能.研究结果表明,该新型调制器可以在很宽的频带内实现调制速度的匹配和阻抗匹配,半波驱动电压为2.56 V,特性阻抗为55.3Ω.     

Multipatches multilayered UWB microstrip antennas

The authors present multipatches multilayered ultra-wideband (UWB) microstrip antennas. The antenna comprises a driven patch radiator with five parasitic patch radiators. Two antennas with different dielectric substrate combinations are studied. The antenna with low-high-low dielectric constant substrate combination (Antenna no. 1) has an improved performance in terms of impedance bandwidth, gain, overall antenna size and beam-squinting over the antenna with low-low-low dielectric constant substrate combination (Antenna no. 2). The low-high-low dielectric constant combination consisting of three dielectric substrates, namely low dielectric constant (ϵr = 3.38) for both bottom and upper substrate but, high dielectric constant (ϵr = 6.15) for middle substrate. Five parasitic patches and multi-dielectric layers are used for wide impedance bandwidth and less boresight gain variation with frequency. A measured 10 dB return loss bandwidth of 48% with boresight gain .5.0 dBi is achieved. Antenna no. 1 can have 8% wider impedance bandwidth, 40% overall area reduction and less beam-squinting compared with Antenna no. 2.     

GaAs超高速光调制器的研制

从理论与实验两方面研究了ＧａＡｓ定向耦合型行波光调制器，首次报导了重掺杂ｎ＾＋型薄层对电场分量相当于导体，对磁场分量相当于绝缘体这一发现；首次提出了一种具有对称宽电极的新型结构，并研制成功开关电压为８．５Ｖ，微波折射率为３．６，在３０ＧＨｚ情况下传输损耗小于１０ｄＢ／ｃｍ，根据ｓ参数测试３ｄＢ带宽达到３２ＧＨｚ的行波调制器。     

Investigation of adjacent spacing dependent microwave absorption properties of lamellar structural Ti3C2Tx MXenes

Ti₃C₂Tx MXenes and their composites play a vital role in the research on microwave absorbing materials. Herein, the different interlamellar spaces of Ti₃C₂Tx MXene materials were prepared by an etching process. The dependence of the microwave absorbing properties of the Ti₃C₂Tx MXene nanosheets on different interlamellar spaces was studied. The complex permittivity, dielectric loss, impedance matching characteristic and the minimum reflection loss (RL) value with the variation in interlamellar space were systematically investigated. Results showed that 40% ratio paraffin-bonded composites (S3) have a strong electromagnetic wave absorption performance and large effective absorbing bandwidth. The maximum RL reaches −36.3 dB at 4.67 GHz with the thickness of 4.5 mm, ascribed to its a high dielectric loss and good impedance matching characteristics. The RL value of Ti₃C₂Tx MXenes is strongly dependent on the inter-lamellar space. The enhanced microwave absorption originates from the unique 2-D structure, good impedance matching characteristics, and enhanced space-charge polarization effects. This work provides a new avenue for exploring high-performance microwave absorbers based on MXene materials.     

磁控反应溅射制备的Ta2O5薄膜的光学与介电性能

采用直流磁控反应溅射技术，在不同的Ar/O2比条件下制备了系列Ta2O5薄膜样品，采用紫外．可见光透射光谱和椭偏光谱测试分析技术，研究了Ta2O5薄膜在可见光范围内的透射率、折射率和消光系数；同时还采用HP 4192A阻抗分析仪测试分析了样品在500Hz～13MHz频段的介电谱，结果表明在300～700nm的可见光波长范围内，氧化钽薄膜的消光系数k→0，折射率＞2．0，透射率大约80％。500Hz下的低频介电常数5的典型值为20.1。损耗角正切tgδ为19.9。     

Cornstalk-derived macroporous carbon materials with enhanced microwave absorption

Biomass transformation is being considered as a green and sustainable strategy for carbon-based functional materials in many fields. To produce porous structure favorable for microwave absorption, we demonstrate herein the successful synthesis of macroporous carbon materials with cornstalk as a biomass precursor. It is found that two kinds of typical biological structures in cornstalk, linear vascular bundles and parenchyma cells, can be well preserved during high-temperature pyrolysis. Mercury intrusion porosimetry and N₂ adsorption indicate that these cornstalk-derived carbon materials have very high porosity, which is mainly from desirable macroporous structure rather than conventional micro/mesopores. Electromagnetic (EM) analysis reveals that dielectric loss is the only pathway for the consumption of EM energy, and high pyrolysis temperature favors strong dielectric loss through conductive loss and interfacial polarization loss. Meanwhile, pyrolysis temperature also affects the matching degree of characteristic impedance. When the pyrolysis temperature reaches 750 °C, good dielectric loss and impedance matching endow the sample (CSC-750) with excellent microwave absorption performance, including strong reflection loss, broad response bandwidth, and relatively thin absorber thickness. The advantages of macroporous structure are further highlighted in impedance matching and multiple reflection by comparing with a macropore-free counterpart.

     

Broadband NIR emission in sol-gel Er(3+)-activated SiO2-Ta2O5 glass ceramic planar and channel waveguides for optical application

An Er(3+)-doped SiO2:Ta2O5 optical channel waveguide and nanocomposite were prepared by the sol-gel route at a Si:Ta 50:50 molar ratio. Channels with an excellent surface profile were easily and quickly fabricated by focusing a femtosecond laser onto the surface of multilayered films deposited on SiO2/Si substrates. In parallel, the same sol used to prepare the film was annealed at 900, 1000, and 1100 degrees C for 2 h, to get the nanocomposite materials. A broadband NIR emission around 1538 nm, assigned to the 4I13/2 --> 4I15/2 transition of the Er3+ ions was observed in the nanocomposites of amorphous SiO2 containing dispersed Ta2O5 nanocrystals. The 4I13/2 lifetime and emission bandwidth depend on the annealing temperature. In conclusion, Er(3+)-doped SiO2:Ta2O5 channel waveguides and nanocomposites are promising materials for photonic applications.     

FeCo/PPy纳米复合材料的合成及其电磁性能调控

为进一步改善电磁波吸收材料的阻抗匹配、提高吸收强度,本工作以液相还原法制备不同反应时间的FeCo磁性纳米颗粒,经表面修饰后通过原位氧化聚合,合成不同系列的FeCo/PPy纳米复合材料。结果表明,当FeCo反应时间为2h时,所合成的FeCo/PPy复合材料在14.45GHz、匹配厚度为2mm时最小反射损耗可达-38.19dB,有效带宽为5.45GHz(12.24～17.69GHz)。磁性纳米颗粒引入聚吡咯,有效降低了聚吡咯的复介电常数,优化了阻抗匹配,降低了对电磁波的反射;同时,在FeCo磁性纳米颗粒的磁损耗、PPy的介电损耗以及异质界面极化损耗等多重作用下,FeCo/PPy纳米复合材料对电磁波有着较好的吸收性能。     

Synthesis of covalently bonded reduced graphene oxide-Fe3O4 nanocomposites for efficient electromagnetic wave absorption

High-performance electromagnetic (EM) wave absorbers,covalently bonded reduced graphene oxide-Fe3O4 nanocomposites (rGO-Fe3O4),are synthesized via hydrothermal reaction,amidation reaction and reduction process.The microstructure,surface element composition and morphology of rGO-Fe3O4 nanocomposites are characterized and corresponding EM wave absorption properties are analyzed in great detail.It demonstrates that Fe3O4 nanoparticles are successfully covalently grafted onto graphene by amide bonds.When the mass ratio of rGO and Fe3O4 is 2∶1 (sample S2),the absorber exhibits the excellent EM wave absorption performance that the maximum reflection loss (RL) reaches up to-48.6 dB at 14.4 GHz,while the effective absorption bandwidth (RL＜-10 dB) is 6.32 GHz (11.68-18.0 GHz) with a matching thickness of 2.1 mm.Furthermore,radar cross section (RCS) simulation calculation is also adopted to evaluate the ability of absorbers to scatter EM waves,which proves again that the absorption performance of absorber S2 is optimal.The outstanding EM wave absorption performance is attributed to the synergistic effect between dielectric and magnetic loss,good attenuation ability and excellent impedance matching.Moreover,covalent bonds considered to be carrier channels can facilitate electron migration,adjust EM parameters and then enhance EM wave absorption performance.This work provides a possible method for preparing efficient EM wave absorbers.     

Enhanced microwave absorption performance of graphene/doped Li ferrite nanocomposites

In the present study, Microwave absorbing Li-Sr, Li-Co ferrite nanoparticles and RGO/Li-Sr, RGO/Li-Co ferrite nanocomposites containing Li ferrite and reduced graphene oxide (RGO) were synthesized to further improve the microwave absorption performance of Li ferrite nanoparticles (LiFe₅O₈). The Li-Sr and Li-Co nanoparticles were synthesized by thermal treatment method, the RGO/Li-Sr and RGO/Li-Co nanocomposites were obtained by a polymerization method and were characterized by different techniques. The electromagnetic wave absorption properties of the samples were evaluated by vector network analyzer (VNA) in the frequency range of 2–18 GHz. The magnetic and dielectric loss, impedance matching, and electromagnetic wave absorption of the samples are significantly improved through the addition of RGO. Experimental results revealed that the RGO/Li-Co nanocomposite considerably increased microwave absorption. The minimum reflection loss (RL) of RGO/Li-Co also was found to reach −46.80 dB at the thickness of 3 mm and the effective absorption bandwidth (≤-10 dB) amounted to 6.80 GHz (from 10.52 to 17.32 GHz), which was much higher in comparison with pure Li and Li-Co ferrites nanoparticles. Due to the synergistic effect between magnetic loss and dielectric loss and the good impedance matching, the RGO/Li-Co nanocomposite may be regarded as a new candidate for microwave absorbing materials characterized with a broad effective absorption bandwidth at thin thicknesses.     

微波多层板基材的性能要求

介绍了微波多层板所用基材的性能参数,重点阐述了材料的介电常数、介质损耗、热胀系数、特性阻抗对多层板性能的影响。通过对微带线特性阻抗公式的理论计算,得出了带线的线宽W、导体层的厚度t、介质的厚度h以及介电常数ε1的精度对特性阻抗Z。的影响程度。这4个因素中,介质的厚度h和带线的线宽W对特性阻抗Z。的精度影响最大。总结了国内外微波介质材料的研究情况,优选了适合于制造微波多层板的材料。     

Piezoelectric tantalum pentoxide studied for optical tunable applications

Piezoelectric transparent thin films are of great interest for use in tunable filters. We present experimental results on Ta2O5 single layers coated on fused-silica substrates with an electron-beam deposition process. Above 450 degrees C, coatings change from an amorphous to a polycrystallized structure. When this structure shows a preferred orientation matching the piezoelectric tensor of the Ta2O5 crystal and the external electric field, variation in the piezoelectric layer thickness is expected. We detail experimental results in terms of optical (spectrophotometric and scattering measurements) and nonoptical characterizations (x-ray diffraction and scanning electron microscopy). Then the resultant thickness variation under oscillating applied voltage is measured with an extrinsic Fabry-Perot interferometer setup.     

Accessory ligand strategies for hexacyanometallate networks deriving perovskite polycrystalline electromagnetic absorbents

The controllable adjustment of electromagnetic(EM)properties for high-efficiency EM absorbents are indispensable,nonetheless,rare in crystals engineering regulation.Herein,for the first time,regulated amount of sodium citrate was employed as accessory ligand of cobalt cation in aqueous solution to kinet-ically assist the controllable fabrication of Prussian blue analogs(PBAs)and corresponding lanthanide perovskite hybrid CoFe alloy polycrystals.Especially,the multi-phase features were analyzed based on Rietveld refinement of XRD patterns,illustrating the existence of distortions,defects and heterogeneous interfaces in resultant polycrystals.Benefited to the dielectric and magnetic adjustment,polycrystalline absorbents achieved excellent impedance matching and EM attenuation,as the minimum reflection loss of CoFe/LaFeO3 and CoFe/LaFeO3/La2O3 reached-44.13 and-33.95 dB,ranking broadest effective bands up to 4.88 and 3.36 GHz.The validity of the strategy provided a novel sight into the controllable fabrication of high-performance magnetic semiconductor polycrystalline devices.     

Investigation on the broadband electromagnetic wave absorption properties and mechanism of Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-nanosheets/reduced-graphene-oxide composite

A cobaltosic-oxide-nanosheets/reduced-graphene-oxide composite (CoNSs@RGO) was successfully prepared as a light-weight broadband electromagnetic wave absorber.The effects of the sample thickness and amount of composite added to paraffin samples on the absorption properties were thoroughly investigated.Due to the nanosheet-like structure of Co3O4,the surface-to-volume ratio of the wave absorption material was very high,resulting in a large enhancement in the absorption properties.The maximum refection loss of the CoNSs@RGO composite was-45.15 dB for a thickness of 3.6 mm,and the best absorption bandwidth with a reflection loss below-10 dB was 7.14 GHz with a thickness of 2.9 mm.In addition,the peaks of microwave absorption shifted towards the low frequency region with increasing thickness of the absorbing coatings.The mechanism of electromagnetic wave absorption was attributed to impedance matching of CoNSs@RGO as well as the dielectric relaxation and polarization of RGO.Compared to previously reported absorbing materials,CoNSs@RGO showed better performance as a lightweight and highly efficient absorbing material for application in the high frequency band.     

离子束溅射沉积Ta2O5光学薄膜的实验研究

根据择优溅射的理论,在不同的通氧方式下,详细分析了离子辅助对离子束溅射沉积Ta2O5薄膜光学特性的影响。结果表明,在薄膜生长的过程中,由于氩离子的轰击作用,薄膜中的氧原子被优先溅射出来,造成了薄膜化学剂量比失调、吸收增加。但是,通过优化辅助离子源中氧气的比例,可获得合理化学剂量比、低损耗的Ta2O5薄膜。     

SiCNW-Cf/LAS复合材料的制备和电磁波吸收性能EI北大核心CSCD

采用热蒸发法,以乙炔黑为碳源,在碳纤维(Cf)布上制备不同摩尔硅碳比的SiC纳米线(SiCNW)。通过浆料浸渍及真空烧结工艺,以不同摩尔硅碳比下制备的SiCNW-Cf作为中间夹层制备SiCNW-Cf/LAS(Li2O-Al2O3-SiO2)复合材料。结果表明:随着摩尔硅碳比的减小,SiCNW的直径不断减小,产量先增加后减小,并在摩尔硅碳比为1∶3时达到最高。摩尔硅碳比为1∶1时,所制备的SiCNW-Cf/LAS具有对电磁波的最低反射损耗-40.9dB(7GHz,3mm)。摩尔硅碳比为1∶3时,所制备的SiCNW-Cf/LAS具有吸收电磁波的最大有效带宽4.61GHz(Ku波段,1.5mm)。SiCNW-Cf/LAS复合材料优异的吸波性能归因于其对电磁波较高的介电损耗、散射损耗以及LAS对材料与空间阻抗匹配的调整。     

Topographic measurements of supersmooth dielectric films made with a mechanical profiler and a scanning force microscope

The roughnesses of five supersmooth dielectric films of Si(3)N(4), TiO(2), HfO(2), Ta(2)O(5), and Al(2)O(3) prepared by an ion-beam-sputtering technique were measured with a commercial Talystep mechanical profiler and a sensitive Leica WYKO SPM30 scanning force microscope (SFM) to determine how much roughness the films added to the ～1-?-rms roughness fused-silica substrates on which they were deposited. In all cases the increase in roughness for the three-quarter-wave optical thickness films was a small fraction of an angstrom. SFM measurements showed that the topography of the Ta(2)O(5) and Al(2)O(3) films was less random than that of the other film materials and the substrates.     

Ultrabroad Band Microwave Absorption of Carbonized Waxberry with Hierarchical Structure

Developing microwave absorption materials with broadband and lightweight characters is of great significance. However, it is still a great challenge for carbonized biomass without loading magnetic particles to cover the broad microwave frequency. Herein, it is proposed to carbonize freeze‐dried waxberry to make full use of its natural hierarchical gradient structure to target the ultrabroad band microwave absorption. The carbonized freeze‐dried waxberry shows radial‐gradient and hierarchical structure. The different components of hierarchical waxberry demonstrate gradient dielectric properties: the outer component shows anisotropic dielectric constants with smaller value, while the inner core shows higher dielectric constants. This gradient dielectric property is beneficial to the impedance matching and strong polarization. As a result, the bandwidth of carbonized waxberry exhibits an ultrabroad band microwave absorption, ranging from 1 to 40 GHz with the reflection loss value below ?8 dB. Meanwhile, the bandwidth can cover from 8 to 40 GHz when the reflection loss is below ?15 dB. The ultrabroad microwave absorption is attributed to the hierarchical radial‐gradient structure of carbonized waxberry, which provides good impedance matching with air media. This achievement paves the way for the exploitation of natural hierarchical biomass as a superlight and broadband high‐performance microwave absorption material.     

Hollow waveguides with low intrinsic photoluminescence fabricated with Ta(2)O(5) and SiO(2) films

A type of integrated hollow core waveguide with low intrinsic photoluminescence fabricated with Ta(2)O(5) and SiO(2) films is demonstrated. Hollow core waveguides made with a combination of plasma-enhanced chemical vapor deposition SiO(2) and sputtered Ta(2)O(5) provide a nearly optimal structure for optofluidic biofluorescence measurements with low optical loss, high fabrication yield, and low background photoluminescence. Compared to earlier structures made using Si(3)N(4), the photoluminescence background of Ta(2)O(5) based hollow core waveguides is decreased by a factor of 10 and the signal-to-noise ratio for fluorescent nanobead detection is improved by a factor of 12.