An application of the diffractor grating to the 11-Gc/s microwave systems

The diffractor grating is a new version of the microwave passive repeater developed to improve the transmission qualities of links utilizing mountain diffraction. It has special advantages in the high-frequency region, as well as in the 11-Gc/s common carrier band, where the construction of a large-aperture flat reflector encounters difficulties and becomes uneconomical. Principles and characteristics of diffractor grating are given with test results. Various factors affecting the diffractor grating behavior are investigated, and comparisons are made with the double-plane reflector system. The diffractor grating is shown to be applicable to short-haul microwave systems and possibly reduce construction costs.     

Millimeter wave twist reflector design aspects

A millimeter-wave twist reflector design procedure is described. An effective dielectric constant for capacitive susceptance correction for a unidirectional planar grating at the interface of free space and dielectric material in the twist reflector environment is introduced. The loss factor of the dielectric material is taken into account for the prediction of twist reflector performance. With the introduction of these corrections experimental results are found to be in close agreement with the theory. Normalized curves for the design of twist reflectors in terms of grating parameters, dielectric substrate relative permittivity, and dielectric material thickness are presented. Experimental results are given     

Surface-relief type Bragg grating reflector fabricated after overcladding removal

A novel silica-based Bragg grating reflector on Si substrate is described. The reflector is formed on a core whose overcladding layer is removed by RIE until is is level with the core surface. The reflector which comprises a rectangular relief type grating only 1.6 mm long has the advantages of a highly controllable Bragg wavelength and a high reflectivity of 76% for the TE mode.<>     

A novel frequency-scanned reflector antenna

Theoretical and experimental results are presented for a frequency-scanned antenna composed of a line source and a frequency-scanned reflection grating that is shaped to a cylindrical reflector. The principle considering is to select the grating geometry such that the first higher-order diffracted wave propagates and serves as the frequency-scanned beam. An analytical solution for the cylindrical reflector geometry that gives a line focus is given. The grating structure considered consists of an array of dipoles placed over a ground plane. The design of the dipole grating for optimum blazing (i.e., for optimal power conversion from the incident wave to the diffracted wave) is discussed. For the theoretical analysis Floquet's theorem and the method of moments are used     

Grating-Induced Dual Mode Couplings in the Negative-Index Slab Waveguide

In a slab waveguide where negative-index materials are adopted as a core layer, we show that a single-period grating can act as both a Bragg reflector and a transmission grating, which enables us to achieve dual-wavelength mode couplings via a single grating.     

毫米波光栅谱仪分辨率的研究

对具有一定入射角的波束经球面镜聚焦后焦点区域场的分布进行理论计算与实验测试,结果表明:在毫米波光栅谱仪(25～100GHz)中大球面镜聚焦系统明显限制了频谱分辨率.增大光栅对波束的衍射角是减小和消除这一限制的有效方法.     

Characterization of effects of periodic and aperiodic surface distortions on membrane reflector antennas

The focus of this paper is to characterize the effects of periodic and aperiodic surface distortions on the performance of membrane reflector antennas. Since the surface of this class of reflector antennas is very thin, it is susceptible to various types of periodic and aperiodic distortions. The particular antenna dimensions used for this study are similar to the specifications for the JPL/UCLA half scale model of second generation precipitation radar (PR-2) mission reflector. Analytical expressions are introduced to model periodic and aperiodic surfaces and based on these models the effects of distortions on the radiation performance of the antenna are simulated. Aperiodic distortions are more realistic cases of distortions due to the fact that the period of the distortions is not constant through out the reflector surface. For each case, far-field patterns of the reflector are simulated and it is shown that closed-form expressions can then be derived which result in a very efficient computational method to predict some of the unique features of these patterns including location and level of observed grating lobes. Furthermore, based on spatial Fourier analysis of the surface distortion, it is shown that deviation from periodicity in the distortions of reflector surface results in lowering these grating lobes. Parametric studies have been performed to provide design guidelines for acceptable surface behavior for large deployable membrane reflector antennas for future space borne missions.     

Metallic photonic band-gap materials (MPBG) as angular selective reflector or radome: Application to antenna grating lobe reduction

This paper presents numerical and experimental results on metallic photonic band-gap materials (mpbg), composed of metallic wires and used as antenna reflector or radome. Attention is focused on mpbg angular response. In fact, with specified angular characteristics, MPBG materials can be interesting in order to reduce antenna grating lobes. One possible grating lobe reduction solution is based on the use of mpbg as angular filter. The radiation characteristics obtained with this solution are then improved by using a mpbg reflector to enhance the gain. Regarded to a classical metallic reflector, 20 dB and 12 dB gain improvement in the theoretical and in the experimental cases are respectively obtained, when the reflector is composed of more than two layers. The scanning performances are also presented. We show that angular filtering characteristics can be improved either by changing the array interface or by changing the mpbg lattice. In order to select the structure with the best angular behavior, an experimental and numerical characterization method is also presented.     

低插损高频SAW滤波器的研究

采用单层膜、梯形结构基于128°YX-LiNbO₃材料研究了Al电极厚度、叉指占空比、反射栅周期、拓扑结构对插损、带外抑制和矩形度的影响。为了降低带内波动和插入损耗,该文设计了一种叉指换能器(IDT)型反射栅结构,该结构对采取优化措施前后谐振器的带内最大尖峰损耗分别降低了8.84%和0.55%。最后采用此反射栅结构设计了一款低插损高频声表面波(SAW)滤波器,有限元仿真结果表明,该滤波器的中心频率为2.520 5 GHz,插入损耗为-0.502 12 dB,带外抑制大于30 dB,-3 dB损耗带宽大于98 MHz。     

Analysis of a dual grating-type surface emitting laser

The grating-coupled surface emitter (GSE) consists of a gain section between two grating sections, which are not necessarily identical. The gratings act as both distributed Bragg reflectors and output couplers. An analysis that applies to arbitrary grating shapes and has provisions to include the presence of a substrate reflector to reduce the radiated power into that medium is carried out. Thresholds, differential efficiencies, and far-field patterns are compared for the low-threshold longitudinal modes of the system. Examples illustrating variations in tooth shapes and heights, waveguide loss, the presence of a substrate reflector, and detuning from the Bragg condition are included     

A new planar grating-reflector antenna

A planar grating-reflector antenna with frequency-scanning properties is presented. The antenna system is composed of a point feed and a planar reflector consisting of a frequency-scanned reflection grating. The grating geometry must be selected such that the first higher-order diffracted wave propagates and serves as the frequency-scanned beam. A focus feed position for the diffracted field is obtained by allowing the lattice geometry to vary along the reflector surface. Methods for analyzing and designing the new antenna configuration are presented. The antenna concept is demonstrated theoretically and experimentally by the design, evaluation, and test of an experimental antenna operating over the frequency band 9.5-10.5 GHz     

Broad-range wavelength tuning in DBR lasers with super structuregrating (SSG)

Broad-range wavelength tuning is demonstrated in tunable distributed Bragg reflector (DBR) lasers with the super structure grating (SSG) proposed. The SSG is fabricated by electron beam exposure lithography. The grating performance is measured by transmittance characteristics of the SSG reflector. A maximum tuning range of 63 nm is obtained under the CW condition while keeping a single longitudinal mode. In a 50-nm tuning range, the threshold current variation is as low as 5.0-9.5 mA     

A Multilayer-Based High-Performance Multisubpart Profile Grating Reflector

In this letter, a multilayer-based high-performance subwavelength multisubpart profile grating reflector (MPGR) is proposed and fabricated. The properties of the reflector are investigated by rigorous coupled-wave analysis for multilayered grating structures. It is shown that with the properly configured profile and strongly modulated grating layer in transverse-electric polarized wave, the MPGR experimentally demonstrates a broadband reflection spectrum from 1.56 to 1.8 $mu{hbox {m}}$ , very high reflectivity ($> $97%), and good angular insensitivity of about 27.8$^{circ}$.      

SGDBR激光器中取样光栅的理论和实验研究

讨论了取样光栅分布布拉格反射激光器(SGDBR)中取样光栅对激光器调谐范围、输出功率和光谱质量的影响,介绍了其设计流程,并据此对SGDBR进行了实验研究.其取样光栅的反射谱和设计相符,且在30nm准连续调谐范围内边模抑制比都大于30dB.     

Flexible Bragg Reflection Waveguide Devices Fabricated by Post-Lift-Off Process

Bragg reflection waveguide devices are fabricated on a flexible substrate by using a post-lift-off process in order to obtain highly uniform grating patterns on a wide range. In this process, the flexible substrate formed by spin-coating on a silicon wafer is lifted-off at the end of fabrication procedures. The flexible Bragg reflector exhibits very sharp transmission spectrum with a 3-dB bandwidth of 0.1 nm and a 10-dB bandwidth of 0.4 nm, which is provided by the grating pattern with excellent uniformity. Athermal operation of the flexible Bragg reflector is also demonstrated through the optimization of thermal expansion property of the plastic substrate by controlling the thickness of two polymer substrate materials. The flexible substrate made of 0.7-mum SU-8 layers sandwiching 100-mum NOA61 film provides an optimized thermal expansion property compensating the thermooptic effect of the polymer waveguide. The temperature dependence of the Bragg reflector is reduced to -0.011 nm/degC by the plastic substrate.     

单片集成倾斜SOA的宽可调谐取样光栅分布布拉格反射激光器

高功率和宽调谐范围的单片集成倾斜SOA的宽可调谐取样光栅分布布拉格反射激光器被成功制备。倾斜的SOA结构和端面增透膜有效的降低了端面的反射率。器件调谐范围大于38nm,波长覆盖较好,调谐范围内波长输出功率均大于9mW。     

Monolithic integration of widely tunable sampled grating DBR laser with tilted semiconductor optical amplifier

High output powers and wide range tuning have been achieved in a sampled grating distributed Bragg reflector laser with an integrated semiconductor optical amplifier. Tilted amplifier and anti-reflection facet coating are used to suppress reflection. We have demonstrated sampled grating DBR laser with a tuning range over 38 nm, good wavelength coverage and peak output powers of more than 9 mW for all wavelengths.     

Circular grating coupled DBR laser with integrated focusing outcoupler

We report on the fabrication and operation of a circular grating coupled, AlGaAs-InGaAs surface-emitting distributed Bragg reflector (DBR) SQW laser with an integrated focusing outcoupler. Electron beam lithography and reactive ion beam etching were used to fabricate the laser with a first-order resonant grating for optical feedback and a separate detuned, chirped second-order grating for outcoupling and focusing the beam.     

Positive/negative reflection-type SAW reflectors on ST-quartz using new fabrication technique

A positive/negative reflection-type (PNR) SAW grating reflector on an ST-quartz substrate utilising both a gold and aluminium strip and its simple fabrication technique requiring no critical mask alignment are described.     

Frequency-scanned reflection gratings with integrated polarizer

A frequency-scanned reflection grating (blazed grating) with polarizer properties is investigated. The grating structure considered consists of a periodic array of double-dipole elements etched on a dielectric substrate and placed over a ground plane. The two dipoles within a periodic cell are displaced and tilted from each other. Numerical results are presented showing that this grating structure can be designed to have the property of efficiently converting the power of an incident linear polarized wave into a circular polarized diffracted wave. A design is also outlined where the grating acts as a twist reflector, converting an incident linear polarized transverse electric wave into a first-order diffracted transverse magnetic wave. The theoretical analysis is based on Floquet's theorem and the method of moments. Experimental results verifying the numerical results are also presented