Matrix analysis of discontinuities in nonreciprocal waveguides: analytical description for magnetooptical slab waveguides

A new analytical formalism to study the effect of discontinuities in a nonreciprocal waveguide has been developed. The analysis is based on 1) the general orthogonality relation obtained from the reciprocity theorem, 2) the modal expansion of the transverse electromagnetic fields within the waveguide, and 3) the continuity of the tangential components of such electromagnetic fields at both sides of the discontinuity. The formalism is presented in a matrix form, which allows the treatment of several discontinuities as a simple summation and product of coupling and propagation matrices. The matrix formalism is developed for magnetooptic waveguides in the three different orientations of the magnetization, and, within this context, two practical applications of magnetooptic isolators are studied.     

Non reciprocal single mode conversion in multilayer magnetooptical waveguides

Multilayer structures are of great interest in the fabrication of single mode devices for Integrated Optics. this work it is shown that a multilayer structure allows not only single-mode behaviour but it enhaces the non-reci procity of the quide.     

Thermal index changes by optical absorption in group III-V semiconductor waveguides

Large fast-relaxing intensity-dependent refractive index changes would make certain all-optical signal processing devices in waveguides feasible. In III-V compound materials, light-induced index changes can arise from any of several physical mechanisms which have different strengths and relaxation times. Index changes from 1.06-μm pulsed and CW Nd: YAG laser excitation were measured in single-mode low-loss InP and GaAs waveguide Fabry-Perot structures. The dominant effect was found to be due to heating of the waveguide volume which accompanies an extremely small amount of free-carrier absorption.     

Integration of high-speed optical taps with InP waveguides

Optical taps are key elements for optical signal processing. The authors demonstrate the high-speed operation of an InGaAs p-i-n photodetector on InP waveguides. For a 300- mu m-long tap that samples 19% of the light propagating in a 7- mu m-wide waveguide, the response time is 50 ps at a 1 V reverse bias. The taps require a simple epitaxial growth and can readily be integrated with electrooptic modulators and other optoelectronic devices for multigigahertz optical signal processing.<>     

Integration of organic semiconductor lasers and single-mode passive waveguides into a PMMA substrate

Efficiently combining active and passive elements in integrated optics is a key ingredient for their successful employment. Here, we present the fabrication of an optimized PMMA substrate structure for improved coupling of laser light generated by organic semiconductor distributed feedback lasers into single-mode deep ultraviolet induced waveguides. For production, electron beam lithography on an oxidized silicon wafer and subsequent reactive ion etching is used to form the feedback grating of the laser. Afterwards, an aligned second electron beam lithography step on top of the grating allows the fabrication of a topographical step of 1.67 μm on the edges of the grating area. Metal is evaporated on this resulting master structure serving as a plating base for electroforming of a Ni tool. The tool is then used for hot embossing of the structure into PMMA bulk material. On a length of 500 μm the imprinted grating lines, having a period of 200 nm, are 100 nm wide and 60 nm high. Aligned deep ultraviolet exposure to induce a passive single- or multi-mode waveguide and co-evaporation of the active material Alq₃:DCM finish the coupling region. This structure optimizes the coupling of laser light generated in the laser structure into the passive waveguide. In combination with microfluidic channels, the laser light can be considered for sensing applications on a PMMA lab-on-chip system.     

Integration of a multimode interference coupler with a corrugated sidewall Bragg grating in planar polymer waveguides

We demonstrate the integration of a 3-dB multimode interference coupler with a corrugated sidewall Bragg grating in planar polymer waveguides by direct electron beam writing. Both transmission and reflection spectra of the Bragg grating are measured through this integrated device directly. We use the thermooptic effect to tune the integrated waveguide grating, achieving a tuning range of 6.2 nm and a bandwidth variation of 0.3 nm within a temperature change of 62/spl deg/C.     

硅基波导、光探测器和CMOS电路的集成

对于集成光学器件和微电子电路制作，应用了驻波监控指示技术（ＳＷＡＭＩ）、局部氧化技术（ＬＯＣＯＳ）、光波导和探测器的平接、漏波，以及镜耦合技术。文章介绍了硅基光波导、光探测器和ＣＭＯＳ电路的单片集成技术。讨论了集成工艺以及静态和动态测量结果     

Integration of thin film optoelectronic devices onto micromachinedmovable platforms

The integration of a thin film optoelectronic device onto a micromachined movable platform is reported in this letter. This micro-opto-mechanical system, consisting of a thin film AlGaAs/GaAs double heterostructure p-i-n detector integrated onto a polyimide micromachined platform on silicon, has applications which range from fiber optic coupling to sensors. Fiber optic coupling is demonstrated using a stationary fiber positioned above the thin film detector. By applying a voltage between the platform and actuation strips, the platform moves and a change in fiber to detector coupling is observed     

III-V族化合物HBT模型参数提取

对III-V族化合物HBT模型本征集电极和发射极电流方程进行了改进，加强了模型的拟合能力. 给出了HBT在零偏和冷偏下的等效电路模型，为精确提取基-射、基-集结本征和外围结电容，开发出一种新的、从零偏条件下测量所得S参数中直接提取本征、外部结电容的方法，该方法同时允许本征集电极电阻（Rci) 的解析提取. 运用该方法精确提取了一发射结面积为180μm2的GaAs HBT器件参数，验证结果表明，算法精度可达40GHz.     

Integration of waveguides and photodetectors in SiGe for 1.3 μmoperation

The integration of single-mode rib waveguides and photodetectors in silicon using MBE-grown SiGe-layers is reported. Short photodetectors exhibit dark currents below 200 nA at 7 V reverse bias. For the fiber-waveguide-detector coupling an overall quantum efficiency of 11% has been achieved at 7 V reverse bias for λ=1.3 μm. The maximum bandwidth is 2 GHz     

Thermal Conductivities of III-V Antimonides

Thermal parameters of various III-V antimonides,especially the quaternary lattice matched to GaSb or InAs substrates as well as some strained ternaries,have been investigated theoretically.Results show that at most composition region many ternary and quaternary antimonides exhibit rather lower thermal conductivity compared to related binaries,and the reason has been discussed.The thermal designing rule of the lasers and other power devices using those antimonides also has been discussed.     

Thermal Conductivities of Ⅲ-Ⅴ Antimonides

Thermal parameters of various Ⅲ-Ⅴ antimonides, especially the quaternary lattice matched to GaSh or InAs substrates as well as some strained ternaries, have been‘investigated theoretically. Results show that at most composition region many ternary and quaternary antimonides exhibit rather lower thermal conductivity compared to related binaries,and the reason has been discussed. The thermal designing rule of the lasers and other power devices using those antimonides also has been discussed.     

Energy spectrum and magnetooptical properties of a D (−) center in a quantum constriction

The states of the electron localized at a donor in the quantum constriction with parabolic electron potential in the presence of a magnetic field that is longitudinal with respect to the axis of the constriction are considered. The dispersion relation for electrons was derived analytically in the context of the model of the zero-radius potential taking into account the effect of a magnetic field on the D ^(?) state in the quantum constriction. It is found that the singularity in the electron spectrum in the quantum constriction manifests itself in the dependences of the binding energy of the D ^(?) state and the edge of the extrinsic-absorption band on the effective length of the constriction. The evolution of both the binding energy of the D ^(?) state and the spectrum of intrinsic magnetooptical absorption in the quantum constriction as the strength of a longitudinal magnetic is varied is studied. The results are compared with those in the case of the D ^(?) state in a quantum wire.     

Key aspects in the modeling of concentrator III-V solar cells and III-V thermophotovoltaic converters

The development of III-V concentrator solar cells and thermophotovoltaic converters is at a critical point in which both sophisticated technology and an accurate modeling are required. This paper emphasizes the aspects relating to the modeling of multijunction solar cells for the concentration of applications and thermophotovoltaic converters. In the case of solar cells, the key aspects are

• —Necessity of three-dimensional modeling
• —Consideration of real conditions of operation
• —Critical review of material parameters.

For TPV converters, the aforementioned aspects are also to be applied. Preliminarily, the material parameters of the less mature thermophotovoltaic semiconductors must be specified or even measured.     

Low-temperature Pd bonding of III-V semiconductors

The authors have developed a low-temperature Pd bonding technique for integrating InP structures onto GaAs substrates. The solid phase reactions of Pd with both InP and GaAs allows Pd to be used as a sandwiched ohmic contact between two dissimilar materials. The InP-Pd-GaAs interfaces have been characterised by scanning electron microscopy, optical reflectance, and electrical transport measurement     

Performance characterization of III-V power devices

The power performance of GaAs/AlGaAs pseudomorphic high electron mobility transistors (PHEMTs) has been modeled by using the statistical Design of Experiment approach. Empirical models for the small signal gain, output power and power added efficiency have been developed. The “walk-out/in” phenomenon has been observed in the devices as a result of power measurements. The evolution of surface photovoltage spectra after RF power stress indicates accumulation of positive electrical charge in the buffer and the surface layer of the devices.     

Atomic-layer-deposited tantalum silicate as a gate dielectric for III-V MOS devices

TaSiO_x thin films with Si/(Ta + Si) mole fractions between 0 and 0.6 have been deposited using atomic-layer deposition on Si and InGaAs at 250 °C. Interface defects on InGaAs were on the order of 10¹² cm⁻² eV⁻¹, which is comparable to state-of-the-art Al₂O₃ deposited by atomic-layer deposition using Al(CH₃)₃ and H₂O while the dielectric permittivity of TaSiO_x is considerably higher.     

Anisotropy of magnetooptical absorption of quantum dot-impurity center complexes

The magnetooptical properties of 〈quantum dot〉-〈impurity center〉 complexes formed in a transparent insulator host were studied. In order to describe one-electron states of a quantum dot, a parabolic model of the confinement potential was used. In terms of the zero-range potential model in the effective-mass approximation, the coefficient of extrinsic absorption of light polarized parallel and perpendicular to the direction of an external magnetic field (longitudinal and transverse polarizations, respectively) was calculated taking into account variance in the quantum-dot size. It was shown that, in the case of longitudinal polarization, the edge of the extrinsic-absorption band shifts in a magnetic field to shorter wavelengths and the absorption coefficient increases several times. In the case of transverse polarization, the quantum-dimensional Zeeman effect is observed in the extrinsic-absorption spectrum. It was also shown that the anisotropy of the magnetooptical absorption is a nonmonotonic function of the frequency of light and does not depend critically on the impurity-level position.