A coaxial 2D-periodic perforated directional coupler

We propose to couple two coaxial waveguides by 2D periodic perforation in the common wall in order to ensure selective coupling between two waves propagating in these waveguides. In the experiment at a frequency of 10 GHz, the H ₀₁ mode of the internal waveguide was converted to the rotating H ₅₁ mode of the external waveguide with a power loss of several percent.     

Analysis of electrooptically induced waveguides in strontium barium niobate and optical modulators

An electrooptically induced optical waveguide can be formed by applying a DC voltage between electrodes fabricated on the surface of a crystal with strong electrooptic coefficients (for example, strontium barium niobate). Calculations of the refractive index profile and the optical mode size for such waveguides are presented. Approximate solutions for the fundamental mode are used to analyse the power coupling between a single-mode step-profile fibre and these waveguides. The power transmission losses in the straight and S-shaped waveguides are estimated by using a finite-difference beam propagation method (FD-BPM). The calculations predict that a new kind of modulator/switch can be realized with the induced waveguides. The important characteristics of these devices are discussed and compared with LiNbO₃ optical waveguide modulators.     

任意分配比的微波功率分配器

圆波导中TE11模式波的电场在波导壁上随角度按正弦(或余弦)变化.如果在其侧壁上沿径向接两根互相垂直的波导,波导绕轴转动时两根波导中所分配的功率将随旋转角度而变化.这样就可以设计出任意分配比的微波功率分配器.通过HFSS的模拟计算完成了该功分器的设计,同时设计了一个新型的圆波导TE11模式转换器.     

同轴TEM-矩形TE10模式变换器的优化设计

用ＨＦＳＳ软件和网络理论对Ｓ波段同轴ＴＥＭ－矩形ＴＥ１０模式变换器进行了优化设计。同轴波导工作于过模状态,可同时传输ＴＥＭ、ＴＥ１１、ＴＥ２１模。模式变换器可应用于高功率微波的能量提取系统,优化设计方法可用于通过短路活塞来实现调配的同轴－矩表、圆波导－矩形的模式变换器。     

同轴TEM－余矩形TE10模式变换器的优化设计

 用HFSS软件和网络理论对S波段同轴TEM－矩形TE₁₀模式变换器进行了优化设计。其中同轴波导工作于过模状态,可同时传输TEM、TE₁₁、TE₂₁模。模式变换器可应用于高功率微波的能量提取系统,优化设计方法可用于通过短路活塞来实现调配的同轴－矩形、圆波导－矩形的模式变换器。     

用于速调管功率合成输出结构的转向波导设计

 为X波段高峰值功率速调管功率合成输出结构设计了一个工作在9 GHz的转向波导，用于连接功率合成器和速调管输出腔。转向波导结构由中心矩形谐振腔、两个矩形耦合孔和两边的输入输出波导组成；输入和输出波导由速调管输出腔和功率合成器确定，分别工作在TE₁₀和TE₀₁模式，它们相互垂直并偏离矩形谐振腔的中心；中间的矩形谐振腔工作在TM₁₁₀，TE₁₀₁和TE₀₁₁混合模式。这种转向波导结构的3个反射零点构成了较宽的传输通带。将连接转向波导结构的功率合成器加载到速调管输出腔,计算了功率合成器加载后速调管输出腔的间隙阻抗。计算结果表明：功率合成器的加载对输出腔间隙阻抗影响不大。设计的转向波导结构很好地应用到了速调管功率合成输出结构中。     

Measurement of the optical transmission modes and losses of the poled guest–host polymer NAEC/PEK-c planar waveguides

The polyetherketone (PEK-c) guest–host polymer planar waveguides doped with (4′-nitro)-3-azo-9-ethyl-carbazole (NAEC) were prepared. The waveguide films were poled by corona-onset poling at elevated temperature (COPET), and the corona poling setup includes a grid voltage making the surface-charge distribution uniform. By using the prism-in coupling method, the dark-line spectrum given by the reflected intensity versus the angle of incidence have been obtained, and the optical transmission losses of mth modes have been measured for the poled polymer waveguides at λ=632.8 nm. The measurement result showed that the optical loss of the fundamental mode is less than 0.7 dB cm⁻¹ for the TE polarization.     

TE modes in parallel cylindrical surface waveguides

Dispersion equations for TE and TM modes in width-limited waveguides formed by parallel cylindrical surfaces are derived in adiabatic approximation. It is shown that the dominant TE₀₁ mode is strongly localized in the waveguide center.     

Variational analysis of Er:Ti:LiNbO3 waveguide lasers based on Gaussian/two-half Gaussian mode field distribution

Starting with two dimensional, scalar wave equation, a variational equation was established for the fundamental TE and TM modes guided in Ti:LiNbO₃ waveguides on the basis of assuming a symmetric Gaussian mode field function in the width direction and two-half Gaussian trial functions in the depth direction. The controllable waveguide fabrication parameters, including channel width, diffusion temperature, initial Ti-strip thickness and diffusion time, dependent of fundamental mode size, effective pump area, coupling efficiency between pump and laser modes, and the coupling loss between a Ti:LiNbO₃ waveguide and a fiber were numerically calculated for Z-cut Er:Ti:LiNbO₃ channel waveguide lasers at three possible emission wavelengths 1532,1563 and 1576 nm and two possible pump wavelengths 1480 and 980 nm. The calculated results were compared with those of Gaussian/Hermite–Gaussian mode field distribution in detail.     

Design of the spot size for single-mode Ti/Mg:LiNbO3, channel waveguide for optimum coupling with fibers

Abstract

To improve the coupling effciency between fibers and conventional Ti:LiNbO₃ diffused channel waveguides, it is feasible that the elliptical mode pattern of the channel waveguide can be modified by the Ti/Mg double diffusion method. By means of the three-dimensional beam propagation method, we successfully show that the mode size of the waveguide fabricated by this method is well matched to that of the fiber for TE and TM polarizations separately.     

Optically pumped distributed feedback thin film waveguide lasers with multiwavelength and polarized emissions

Zirconia titania organically modified silicate (ZrO₂-TiO₂-ORMOSIL) thin film waveguides of thickness from 0.4 to 7.0 μm were synthesized using low temperature sol–gel method. Narrow linewidth distributed feedback (DFB) lasing was demonstrated in rhodamine 6G-doped ZrO₂-TiO₂-ORMOSIL waveguides. Simultaneous tuning of multiple-output wavelengths was achieved in the dye-doped waveguides by varying the period of the gain modulation generated by a nanosecond Nd:YAG laser at 532 nm. As many as eight separate output wavelengths were observed for a planar ZrO₂-TiO₂-ORMOSIL waveguide of thickness 7.0-μm. The output polarizations of the DFB waveguide lasers can be tuned by varying the polarization of the crossing pump beams. TE and TM optical waves belonging to the same propagation mode were generated by crossing two polarized pump beams, resulting in an effective double of the number of output wavelengths. Continuous tuning of the polarized laser outputs was also achieved by varying the crossing angle.     

Optical propagation of the HE11 mode and Gaussian beams in hollow circular waveguides

The propagation of the HE₁₁ mode and Gaussian beams in hollow oversized circular waveguides is analyzed using optical theories. Different types of waveguides are considered : hollow dielectric or conducting waveguides, dielectric-lined waveguides, corrugated waveguides. General formulas are derived which give the power transmission through these different guides. The best wall materials and structures are determined from a comparison of the waveguide transmissions, at the infrared and millimeter wavelengths. The question of the coupling between the HE₁₁ mode and Gaussian beams is discussed and from a review of coupling coefficients derived before, an optimum value is pointed out. The problem of matching a Gaussian beam into circular waveguides in order to achieve the maximum power transmission is analyzed. These results are of interest for infrared lasers or waveguide applications and for Electron Cyclotron Wave (ECW) systems at the millimeter wavelength.     

Wide-angle low-loss waveguide branching for integrated optics

A new wide-angle, low-loss, symmetrical Y-branch waveguide is proposed. The waveguide configuration utilizes ribs for lateral confinement in the planar guiding region underneath. This Y-branch structure can be fabricated easily without an additional process step. Together with a utilization of the multimode interference effect, a local decrease of the waveguide ridge in the wedge part of the Y-branch reduces the radiation loss. When proper@ designed, the proposed Y-branch has a radiation loss as low as 2.2 dB at a branch angle of 6° with the index difference (Δn/n) as small as 7.1 × 10^-4 at a wavelength of 870 nm in the TE fundamental mode as compared to 12.6 dB for a conventional Y-branch. The proposed method yields corresponding advantages for waveguide designs with a higher Δn/n ratio and can also be adapted in combination with S-branch designs.     

Semi-Analytical Simulation of Titanium-Indiffused Lithium Niobate–Integrated Optic Directional Couplers Consisting of Curved Waveguides

Integrated optic directional couplers consisting of curved waveguides are simulated analytically by solving the Riccati equation. The coupling coefficient between the curved waveguides with a parabolically varying gap and the condition of total power transfer between the waveguides are derived. In order to compute the overall coupling coefficient and hence the power distribution along the waveguides for Ti:LiNbO ₃ curved waveguide directional couplers, the coupling coefficient for straight waveguide couplers is computed for different gaps using the effective-index-based matrix method (EIMM). Finally, the power distribution in the curved waveguides along the length is computed. The method is mostly analytical except the effective-index method and is computationally simple.     

一阶模的滤除及在Y分支和多模干涉结构中的应用

Y分支和多模干涉结构广泛应用于平面光波导器件中，在这些器件中，Y分支和多模干涉结构输出对称性具有重要意义。引入Y分支和多模干涉结构输出的不对称主要原因是这两种结构中产生了一阶导模，设计一种新的耦合器结构，在这个结构中．两根单模波导分别放置在一根多模波导两边，并且单模波导的传播常量与多模波导的一阶模的传播常量相同，这种结构可以将一阶导模滤除。在Y分支和多模干涉结构中使用了这种结构，模拟结果表明，采用这种耦合器的Y分支和多模干涉结构具有非常好的输出对称性。     

A dielectric rod waveguide coupled with metal rectangular waveguide

Measurements have been done in the millimeter wave region on a composite waveguide which comprises a dielectric rod waveguide connecting two metal rectangular waveguides. Such a waveguide has been used by us in a Josephson harmonic mixer installed in a small metal cryostat, to prevent the thermal invasion from outside environment and to transmit both signal and LO waves with small losses. The measured transmission loss, that is caused mainly by the coupling loss between metal rectangular waveguides (TE₁₀ mode) and a dielectric rod waveguide (HE₁₁ mode), has been less than 2dB in the frequency range of 52–104 GHz.     

Frequency dependence of acoustooptic interaction efficiency in anisotropic graded-index waveguide

An analysis of the dependence of the Bragg acoustooptical interaction efficiency of TE modes in a graded-index optical waveguide on the acoustic surface wave (ASW) frequency has been made. It is shown that two waveguides having different optical parameters but the same number of modes are described practically by the same frequency dependence. This conclusion is confirmed by the calculation for two four-mode waveguides on the Y-cut lithium niobate. The frequency dependence for various processes in the range 50÷550 MHz has been experimentally measured.     

对称单负介质包层平面波导的模式特征

系统研究了负μ材料(MNG)作为包层的对称三层平板波导的传输特性. 研究发现,这种波导既支持快波的传播,又支持TE₀,TE₁模式的慢波传输. 其模式特性不同于左手介质波导和传统介质波导,导模存在的模折射率范围要比它们的大. MNG波导的TE₀快波模缺失,且TE_m模(m>1)的传播常数大于TM_m模的传播常数. TE_m模具有双模特征,且与波导的结构参数密切相关,导致波导中的净能流出现负值. 关键词： 单负介质 平板波导 快波与慢波 传播常数     

低阈值极化电压玻璃光波导电光效应的研究

采用热极化技术对掺锗玻璃条形光波导进行极化,通过光纤连接 (单模) 的Mach Zehnder Interferometer 系统测量条形波导内诱导出的电光效应,系统地研究了大气环境下极化条件(极化温度、极化时间、极化电压)对电光效应的影响.结果表明:在最佳极化条件下(406℃、-2.4 kV、20 min),波导内的电光系数为r_TM=0.059±0.001 pm/V, r_TE=0.053±0.001 pm/V,且波导结构中存在一个较低的阈值极化电压(100 V)和阈值极化温度(80℃),此时在波导样品内仍能被激发出可观察的电光效应;实验还发现采用负极化诱导方式产生的电光系数较正极化提高15%左右.     

Wave propagation in uniaxial graded-index optical waveguides

Propagation of guided-modes in uniaxial optical waveguides is investigated. When the optical axis lies in the plane of the waveguide, a coupling between TE and TM modes takes place. Based on the coupled-mode theory, the propagating constants of the hybrid modes, the coupling coefficient and the interaction length are determined. A simple model is proposed to describe the guided mode behaviour. The results are illustrated for the case of Ti-diffused LiNbO₃ waveguide.