Integrated magnetooptic Bragg cell modulator in yttrium irongarnet-gadolinium gallium garnet taper waveguide and applications

An integrated magnetooptic (MO) device which consists of an ion-milled collimation-focusing lens pair and a guided-wave MO Bragg cell modulator in a yttrium iron garnet-gadolinium gallium garnet (YIG-GGG) taper waveguide substrate with dimensions of 6.0×16.0 mm ² has been realized for the first time. Performance characteristics of the waveguide lenses including the focal spot size, sidelobe level and throughput, and that of the integrated MO Bragg cell modulator using the magnetostatic forward volume wave (MSFVW) at X-band carrier frequency including the bandwidth, diffraction efficiency, dynamic range, and frequency resolution have been measured at the optical wavelength of 1.303 μm. Scanning of the focused diffracted light beam by varying the carrier frequency of the MSFVW and RF spectral analysis by simultaneous application of multiple microwave frequencies have been demonstrated     

A new guided-wave lens structure

A guided-wave lens is reported. The present lens structure is realized by embedding a low-index lens-shaped waveguide region in a surrounding higher-index planar waveguide. Very large index differences between the lens region and host waveguide are realizable using this technique, making it possible to fabricate low f-number lenses with low spherical aberration. The lens exhibits excellent off-axis performance, low chromatic aberration, and high polarization independence. A prototype f/2 lens in a GaAs/Ga_0.97Al_0.03As waveguide has been designed and fabricated using Corning 7059 glass and SiO₂ for the lens waveguide structure     

Novel fabrication-tolerant twin-guide laser structure with anexternal passive waveguide

The authors propose a novel quasi-symmetrical twin-guide GaAs/AlGaAs laser structure (QSTGL) with a low-loss external passive waveguide. The device is tolerant to fabrication misalignment and therefore well suited for monolithic integration. Threshold current densities of less than 1.1 kA/cm² and a coupling efficiency between 70 and 80% into the low-loss passive waveguide are achieved     

Design of aplanatic waveguide Fresnel lenses and aberration-freeplanar optical systems

A modification of the waveguide Fresnel lens design that has phase-shifting zones placed on the curved contour is suggested. It is shown that the selection of a suitable shape for this contour allows coma aberration to be eliminated. Computer simulation results are presented to demonstrate the significant improvement of the optical characteristics for curved contour lenses. The aplanatic homogeneous refracting waveguide lenses are also considered. It is found that thick aplanatic refracting lenses and the proposed Fresnel lenses have field curvature aberration of opposite sign. This fact allows planar optical systems free from low-order aberration to be designed by combining refracting and Fresnel lenses. An algorithm for producing such a system is presented     

A quantum-well inversion channel heterostructure as amultifunctional component for optoelectronic integrated circuits

An approach to optoelectronic integration utilizing a universal heterostructure with a single GaAs quantum-well active region is presented. The inversion channel forms the basis of a heterojunction field-effect transistor, a lateral current injection laser, a field-effect modulator, and a waveguide photodetector by simple reconfiguration of the electrodes and device geometry. The fabrication technology has been developed for gigahertz bandwidth applications by utilizing ion implantation techniques for interdevice electrical isolation and surface planarization, and reactive ion-etching to realize a self-aligned transistor-based heterostructure. The design, fabrication, and characterization of various heterostructures are discussed in the context of optoelectronic integration and the implementation of ion implantation disordering to realize low-loss self-aligned waveguides for on chip signal routing. The ultimate performance of the devices using a GaAs quantum well is considered, as well as the development of this technology for improved performance using strained InGaAs wells     

Electrooptic Bragg-diffraction modulators in GaAs/AlGaAsheterostructure waveguides

Reports theoretical and experimental results on electrooptic Bragg-diffraction modulators in GaAs/GaAlAs heterostructure waveguides. The devices utilize the linear electrooptic effect in periodic structures to facilitate spatial modulation of the refractive index in the waveguide. A numerical method was established to solve the waveguide equation and quantify the induced changes in the effective index of the waveguide as a result of reverse bias. The numerical calculation has established the guidelines for an optimum design of the modulator that operates in the Bragg regime. The measured diffraction efficiency of the single-grating Bragg modulator was as high as 90 percent at a driving voltage of 15 V. A device consisting of four such basic diffraction gratings was also fabricated and used to demonstrate the function of scalar addition. The highest bandwidth of the devices that have been measured exceeds 1 GHz. The planar waveguide Bragg modulators offer advantages including lower optical propagation loss, greater fabrication tolerance, and spatial separation between the diffracted and the undiffracted light beams     

Low-index embedded waveguide lenses in GaAs substrates

An integrated optical lens structure which embeds a low-index waveguide lens region in a high-index host waveguide is discussed. The lens has been realized on a GaAs/GaAlAs waveguide using an embedded low-index lens structure of glass/SiO₂. At an f-number of 2 and a wavelength of 1.152 μm, the focal spot size is 2.8 μm. The throughput efficiency is 45% and the angular field of view is 10°     

硫系玻璃在长波红外无热化连续变焦广角镜头设计中的应用

针对市场上现有红外广角镜头大多采用定焦结构且缺乏无热化设计的现状,根据光学变焦系统的设计原理,设计了一种有效焦距范围为10~24 mm（变倍比为2.4:1）、视场角变化范围为34~90、工作波段为8~12 m、F/#为2.8的无热化连续变焦广角镜头。考虑到红外镜头多用在温度变化较大的使用环境中,系统设计选用了硫系玻璃NBU-IR2（Ge20Sb15Se65）以及常规红外材料锗（Ge）和硫化锌（ZnS）制备的六片镜片,通过合理分配各个镜片的光焦度及其空气间隔等参数,在连续变焦设计的基础上实现了无热化的光学设计效果。实验结果显示,系统在-40~60℃的温度范围内均可实现品质良好的红外热成像效果,调制传递函数全视场范围内均大于0.25。系统结构较为紧凑简单、质量较轻,仅在一片硫系玻璃镜片上设计了一处非球面,可有效控制光学系统的加工成本。整体设计适用于车载夜视等应用领域。     

An equal group delay waveguide lens

Analytical and experimental results are presented on a circularly polarized waveguide lens that has much greater bandwidth than conventional waveguide lenses. This is achieved by designing the lens to have equal group delay for all rays from the focal point of the lens to the aperture plane. Haft-wave-plate phase shifters in each waveguide element are then oriented to produce a planar phase front. This results in a lens whose aperture phase distribution remains essentially constant over a much wider frequency range than in conventional waveguide lenses. A comparison with a minimum thickness conventional lens and with a phase compensated (Coulbourn) lens is made. A 46-in X band lens was built and tested over a frequency range from 7-9 GHz to confirm the bandwidth performance.     

Theory of spectral beam combining of fiber lasers

We model the spectral beam combining of a fiber laser array in the external resonator configuration, as proposed by V. Daneu et al. A diffraction integral-based approach is used that leads to design principles for most significant measures of performance, such as efficiency, bandwidth, and beam quality. Sensitivity to alignment and positioning errors is also characterized. Off-axis transform lens aberrations are shown to limit array size, and two design criteria are applied to compare the performance of simple spherical, compound, and aspheric lenses. The results indicate that a simple aspheric lens is superior in meeting the proposed criteria to a well-designed compound (quadruplet) lens with spherical surfaces. Application to the efficient coupling of a laser array to a multimode fiber core is discussed as a final example     

Theoretical analysis of integrated collimating waveguide lens

An integrated collimating waveguide lens is analyzed for applications which require the focusing of an optical beam onto the waveguide of a planar lightwave circuit. The lens has a refractive index profile which is parabolically graded as a function of height to focus light in the vertical plane, and has a convex front face to focus light in the horizontal plane. Analysis based on the propagation of a Gaussian field is used to design a lens pair which minimizes the optical loss for a given propagation length. The beam propagation method is used to identify fabrication tolerances which may have impact on the performance of the lens pair. The lens pair has application in micro-optoelectromechanical (MOEM) switches based on planar optical waveguide circuits.     

Microlens fabricated by the planar process

A novel microlens that can be integrated on a laser-diode substrate by the planar process is proposed. It consists of two microcylindrical lenses fabricated by the planar process, and all of their dimensions are less than 100 μm. One lens is a horizontal focusing lens whose curved shape determines focusing. The other is a vertical focusing lens whose gradient refractive index determines focusing. The relationship between fabrication errors and lens characteristics is quantitatively established by comparing lenses with various fabrication errors. Also a laser diode integrated with the horizontal focusing lens is successfully fabricated without damage     

Indoor signal focusing by means of Fresnel zone plate lens attached to building wall

A simple inexpensive on-wall Fresnel zone plate (FZP) lens for indoor focusing of microwave signals is studied. It consists of concentric metal rings mounted on the outside of an exterior building wall. In our theoretical and empirical work the on-wall FZP lens is illuminated normally by a plane or spherical wave, of vertical or horizontal polarization, but other, more general incidence situations can be treated by similar means. The scalar quasi-optical focusing theory of the free-space zone plate has been modified and used for design and analysis of one-, two-, and three-ring on-wall FZP lenses. It is found that the presence of the wall does not change the FZP lens focusing efficiency significantly, but it has a strong axial defocusing effect. A 2-GHz FZP lens assembly consisting of three metal rings made out of thin antimosquito mesh has a focusing efficiency of about 15 dB (measured) and 14 dB (calculated), and axial defocusing of about 0.22 m. Some variations of on-wall/on-roof FZP lenses and their feasible applications in the microwave/millimeter-wave communication links are also discussed.     

折衍射混合成像光学系统设计

讨论了衍射光学元件的特殊成像性质;提出了带宽积分平均衍射效率的概念和应用;给出了作者在国内外完成的几个折衍射混合成像光学系统的应用实例。包括一个用衍射光学元件复消色差的长焦距光学系统,一个仅由两个镜片构成的CMOS相机光学系统和一个较复杂的中等焦距、大孔径、大视场照相系统。这些系统突破了传统光学系统在结构、性能、体积和重量方面的限制,在光学设计理论上具有重要意义,在工程应用上具有重要价值。还介绍了国外衍射光学制造技术和折衍射混合成像光学系统应用方面的最新进展。     

基于光学保角变换的电磁器件设计

保角变换是基于解析函数的一种非常重要的解析方法,利用保角变换可以将虚拟空间中复杂的边界曲线转化为物理空间中简单的边界曲线,从而求解二维平面场问题。文章主要综述并介绍保角变换在几何光学中的应用,通过控制光线传播来设计完美隐身衣、中继透镜、波导弯角和透镜天线等新型电磁器件。最后利用射线追踪仿真和全波仿真对设计加以证明。     

High-power constant-index lens antennas

The results of a study to develop a high temperature dielectric lens antenna for use in the microwave frequency range are presented. The design and fabrication of spherical and hemispherical constant-index lenses are described. Radiation patterns, gain, polarization, and VSWR characteristics of spherical and hemispherical constant-index dielectric lens antennas over the frequency range from 2 to 11 GHz are presented. The results from high-power testing of both spherical and hemispherical constant-index lenses at a 2 kW average power level indicate that this power level causes no degradation in the performance of the lenses.     

Design and fabrication of monolithic optical spot size transformers(MOSTs) for highly efficient fiber-chip coupling

A novel type of monolithic optical spot size transformer realized in the InP/InGaAsP material system combines many desirable features like high fiber-chip coupling efficiency, large spot size transformation, high tolerances for fiber alignment, simple fabrication, and straightforward integrability with other devices. The spot size transformation is accomplished by two waveguide sections tapered in the vertical and lateral directions, respectively. We discuss design issues, describe the fabrication process, give experimental results, and present the monolithic integration of the spot size transformers with a current controlled directional coupler switch     

折衍射混合成像光学系统设计

讨论了衍射光学元件的特殊成像性质; 提出了带宽积分平均衍射效率的概念和应用; 给出了作者在国内外完成的几个折衍射混合成像光学系统的应用实例, 包括一个用衍射光学元件复消色差的长焦距光学系统, 一个仅由两个镜片构成的CMOS 相机光学系统和一个较复杂的中等焦距、大孔径、大视场照相系统。这些系统突破了传统光学系统在结构、性能、体积和重量方面的限制, 在光学设计理论上具有重要意义, 在工程应用上具有重要价值。还介绍了国外衍射光学制造技术和折衍射混合成像光学系统应用方面的最新进展。     

An electromagnetic analysis of a cylindrical homogeneous lens

Radially symmetric lenses are ideally suited for use as multiple-beam antennas. In recent years, several investigations using a geometrical optics approach have indicated that simple lens structures such as homogeneous lenses might be suitable antennas. This paper presents an electromagnetic analysis of a cylindrical homogeneous lens as well as examining in detail the effect upon performance of parameter variations such that engineering and design evaluations can be made. It is shown that a lens with a relative dielectric constant of 3.5 gives the best performance. With the use of simple matching techniques, overall performance comparable to the more complex Luneburg lens is obtained.     

The prospects for ultrahigh-speed VLSI GaAs digital logic

Recent advances of GaAs integrated circuit fabrication technology have made possible the demonstration of ultrahigh performance GaAs digital ICs with up to 64 gate MSI circuit complexities and with gate areas and power dissipations sufficiently low to make VLSI circuits achievable. The authors evaluate, based on the current state of GaAs IC technology and the fundamental device physics involved, the prospects of achieving an ultrahigh-speed VLSI GaAs IC technology. GaAs IC fabrication and logic circuit approaches is reviewed. The experimental performance results are compared for the leading GaAs logic circuit approaches, both for simple ring oscillators and for more complex sequential logic circuits.