Laser-trimming adjustment of waveguide birefringence in optical FDMcomponents

Laser trimming of amorphous-silicon stress-applying films deposited on silica-based single-mode waveguides is demonstrated for controlling waveguide birefringence. Successful applications to polarization-insensitive operation of an optical ring resonator and a Mach-Zehnder interferometer are presented. A phase difference of less than π/100 between TE and TM modes has been attained. It is noted that this laser trimming method can also be applicable to other material devices such as LiNbO₃ and yttrium-aluminum-garnet (YAG), where waveguide birefringence control is a crucial factor in achieving the practical performance of the device     

Design of optical circuit devices based on topology optimization

We apply a design method based on topology optimization technique to optical waveguide devices. In our approach, after a refractive index profile in a design region is automatically generated using a topology optimization method, the obtained structure is redefined using primitive geometries with some design parameters and those parameters are optimized by a sequential linear programming. As numerical examples, we demonstrate how the method can be used for 90/spl deg/ bends and T-branching waveguides with arbitrary splitting ratio.     

Buried rib passive waveguide Y junctions with sharp vertex on InP

A technique is presented for fabricating intersecting waveguides with a sharp junction vertex. This technique was demonstrated by fabricating buried rib waveguide Y branches on InP with a junction vertex width of about 1/8 mu m. These Y branches had lower loss than the regular blunt Y branches but suffered from a dissimilar splitting coefficient between the two arms. This technique may also be useful for fabricating other waveguide elements such as crossed waveguides, zero gap directional couplers, and optical switches. A comparison with theoretical calculations is also given.<>     

基于裁剪造型的等几何分析方法求解波导本征值问题

等几何分析方法使得几何模型和分析模型能够用NURBS统一表达,避免了模型转换过程,但由于其分析域是由张量积面片构成,很难处理截面形式复杂的多联通域问题。裁剪造型等几何分析方法通过背景曲面和裁剪曲线将复杂带孔结构作为一个被NURBS曲线裁剪后的参数区域直接映射而成,只需要一个参数空间就可以表示任意复杂的拓扑结构,该方法既保留了传统等几何分析方法的优点,又实现了对复杂多孔结构的处理。本文将裁剪造型的等几何分析方法扩展到TE波的波导本征值问题,对复杂多孔结构的截止波数进行有效求解,并通过相应的数值算例验证方法的有效性和高精度性。     

An integrated two-stage cascaded Mach-Zehnder device in GaAs

An integrated, cascaded, asymmetric GaAs-AlGaAs Mach-Zehnder (MZ) interferometer, for use in wavelength filtering and time-domain multiplexing, has been designed, fabricated, and tested, This device employs several new passive components, including height-tapered Y-branches, for uniform splitting and recombining, and index-tailored waveguide bends, for low-loss operation. The waveguide bend is designed with a predistorted index profile for minimizing both transition loss and radiation loss. The circuit is fabricated with a resistless, light-induced local etching technique, which enables rapid iterative fabrication of the device geometry to achieve the desired operating path delays. Acting as a wavelength filter, the fabricated device has a -24.3 dB minimum-to-maximum extinction ratio and a -10.5 dB side-lobe suppression ratio. Acting as a pulse-rate multiplexer, the device generates a four-pulse train with a 10-ps pulse-to-pulse separation and an amplitude uniformity of 80% for each input pulse     

Birefringence suppression of UV-induced refractive index with grooves in silica-based planar lightwave circuits

An effective method for suppressing the birefringence of a UV-induced refractive index change is demonstrated for phase trimming of waveguides in planar lightwave circuits. By employing grooves on both sides of the waveguide to control the UV-induced strain, a significant reduction is achieved from 1.46/spl times/10/sup -4/ to 0.11/spl times/10/sup -4/ in the UV-induced birefringence for a /spl pi/ phase shift averaged between the TE and TM modes in a 2 mm-long waveguide.     

Etched Waveguide Grating Variable 1 $,times,$2 Splitter/Combiner and Waveguide Coupler

We propose and test a silicon waveguide grating which serves dual functions: as a 1$,times,$ 2 variable integrated beam splitter/combiner and as an out-of plane diffractive element for coupling light between a single-mode optical fiber and a 500-nm-wide silicon-on-insulator waveguide. An integrated Mach–Zehnder interferometer made with this novel functional element had over 20-dB extinction ratio. The splitting ratio can be tuned by changing the launch position of the optical fiber. The grating coupler had over 36% coupling efficiency and a 1-dB spectral bandwidth of 37 nm.      

A manufacturable technique for implementing low-loss self-imagingwaveguide beamsplitters

A manufacturable technique to implement self-imaging waveguide beamsplitters is proposed and demonstrated. This technique offers low insertion loss and polarization crosstalk, uniform splitting ratios, ease in manufacture, and most importantly application to diverse waveguide material systems. Beamsplitters with splitting ratios that range from 1×2 through 1×17 were fabricated in GaAs-AlGaAs waveguides. For 1×16 splitters integrated with an output ridge waveguide array, the insertion losses in many devices were less than the insertion losses in adjacent straight-through ridge waveguides. The best uniformity spread among the 16 channels was 17.8% and the TE-to-TM and TM-to-TE polarization crosstalks were lower than -25 dB     

Mode evolution type polarization splitter on InGaAsP/InP

A new type of mode-evolution polarization-splitter based on InGaAsP/lnP has been designed and realized. The component uses the large waveguide birefringence of the first-order TE and TM modes in a ridge waveguide made in a heterostructure, In the input section an asymmetric Y-junction acts as a mode converter in order to inject first-order TE- and TM-modes in a polarization-splitting section, which consists of a Y-junction formed by a bimodal and a monomodal waveguide. In the output section a third Y-junction is connected to the bimodal waveguide to couple the first-order mode to a monomodal output waveguide. Components that are 6-mm long and show polarization splitting at a wavelength of 1.55 μm have been realized. The best splitting ratios are close to -20 dB, which is in agreement with BPM simulations. Excess losses are below 1 dB     

An improved single-mode Y-branch design for cascaded 1:2 splitters

The power splitting ratio of Y-branches based on step index waveguides has been calculated using three-dimensional (3-D) finite-difference beam propagation method (FD-BPM). Due to interference of the guided mode with quasiguided modes generated at distortions of the waveguide the splitting ratio depends on the wavelength and design parameters of the Y-branch. The simulations show how variations of the splitting ratio can be minimized using a mode-filter in the input section without significant increase of losses or component size     

Femtosecond Laser Application to PLC Optical Devices and Packaging

Using tightly focused femtosecond laser pulses, we produce an optical waveguide and devices in transparent materials. This technique has the potential to generate not only channel waveguides, but also three‐dimensional optical devices. In this paper, an optical splitter and U‐grooves, which are used for fiber alignment, are simultaneously fabricated in a fused silica glass using near‐IR femtosecond laser pulses. The fiber‐aligned optical splitter has a low insertion loss, less than 4 dB, including an intrinsic splitting loss of 3 dB and excess loss due to the passive alignment of a single‐mode fiber. Finally, we present an output field pattern, demonstrating that the splitting ratio of the optical splitter becomes approximately 1:1.     

集成光学光纤陀螺芯片

本文首次报道了国内研制的集成光学光纤陀螺芯片,详细描述了其设计考虑与制作。单 Y 型多功能钛扩散铌酸锂芯片包含消光比大于35dB 的薄膜波导偏振器、分束比为49.5/50.5的3dB 分束器/合束器、半波电压小于5伏的相位调制器,光纤—器件—光纤插入损耗为5.4dB。     

MCVD planar substrates for UV-written waveguide devices

A method for fabricating planar silica substrates via modified chemical vapour deposition (MCVD) and a modified fibre drawing technique is presented. Long lengths of planar material are generated from a single substrate offering a potentially low-cost alternative to existing planar substrate deposition processes. Buried straight and splitting waveguide channels, as well as Bragg gratings, are inscribed in the planar material using direct UV-writing technology, and the results are reported     

一种实用波导衰减系数测量系统的设计

以波导耦合理论为依据，设计了集光电为一体的波导衰减系数测量系统。测量以激光为光源，采用双光路法，消除了传统检测显示仪由于光源光强不稳定产生的误差，使得测量结果只与光强的相对变化量有关；利用AD538实时模拟计算芯片，提高了计算精度和运算速度；利用常规仪器设备实现了数字化检测显示，避免了人为主观读数产生的误差．该系统亦可应用于介质折射率及分光镜分光比等光学参量的测量。     

数字修调技术在高速高精度流水线ADC中的应用

数字修调技术采用MOS开关控制电路实现对修调数据的传输和电路拓扑结构的改变,相对于传统的修调技术,数字修调技术具有灵活性、可重复性和低成本等特点.基于0.35μmBiCMOS工艺,对采用数字修调技术的A/D转换电路进行仿真验证.结果表明,设计的A/D转换器,其SFDR达65 dB,INL和DNL分别达到0.35 LSB和0.26 LSB,采样率达到250 MSPS.     

The influence of single-photon absorption on the performance of thetwo-photon waveguide autocorrelator

The propagation loss and the single-photon absorption coefficients in a two-photon waveguide autocorrelator are measured as a function of wavelength. The propagation loss was as low as 1.37 cm^-1 at a wavelength of 940 nm in a device with an Al_0.2Ga_0.8As waveguide core. Using a photocurrent technique, band-to-band absorption was measured for photon energies well below that of the bandgap. It was demonstrated that, although the band-to-band absorption coefficient is small (~10^-2 cm^-1 at a wavelength of 1 μm), it is responsible for reducing the contrast ratio of the waveguide autocorrelator. It is suggested that the single-photon absorption takes place via deep levels with relatively long carrier lifetimes     

A Proposal of a New Dielectric Resonator Construction for MIC's

A compact and high-temperature-stable dielectric resonator having no shielding metal walls nor a conventional frequency tuning screw is described. This resonator consists of a high epsilon/sub r/ dielectric resonator element mounted on a low-loss dielectric mount, a dielectric disk with thin metal film fixed on the resonator element, and a microstrip line substrate on which to mount the constituents. The resonant frequency tuning is made by trimming the metal film on the disk. The TE/sub 01delta/ -mode resonant frequencies are analyzed through dielectric waveguide model application. Less than 1-percent analytical error is presented in comparison with the experimental data for a practical resonator. The frequency tuning limit by metal film trimming is about 7 percent. The unfoaded Q value of 2700 at 8.8 GHz and a 4.4-ppm/deg frequency temperature coefficient are obtained.     

激光微调在光通讯波导器件研制中的应用

目前激光微调在光通讯波导器件的研制方面已得到了应用。本文运用激光微调在波导器件上进行了实验,其中以波导环形器和马赫—曾德尔干涉仪为例,具体讨论了激光微调技术在控制波导双折射方面所表现出的高效,简易,实用等优点。     

A 1.3 μm directional coupler polarization splitter by ionexchange

A glass waveguide polarization splitter for operation in the 1.3 μm wavelength region is reported. The device, which has a symmetric directional coupler configuration, exploits the stress-induced birefringence in K⁺-Na⁺, ion-exchanged waveguides, giving rise to an adequate difference in the coupling lengths for the two polarizations. Starting from the measured potassium concentration (refractive index) profile of the structure and utilizing a combination of the multilayer stack theory and the effective-index method, the normal mode propagation constants and mode field profiles are calculated to determine the polarization splitting length and the extinction ratio, and the results are compared with the experimental data. It is shown that in a given coupler, the splitting occurs at several wavelengths in the 1.0-1.45 μm range. A 25 mm-long coupler, fabricated by thermal diffusion of K⁺ ions in BK7 glass, exhibits an extinction ratio of 18.2 dB at 1.32 μm, in excellent agreement with the simulation results     

Cost-Effective Multimode Polymer Waveguides for High-Speed On-Board Optical Interconnects

Cost-effective multimode polymer waveguides, suitable for use in high-speed on-board optical interconnections, are presented. The fundamental light transmission properties of the fabricated waveguides are studied under different launch conditions and in the presence of input misalignments. Low loss ($sim$0.04 dB/cm at 850 nm) and low crosstalk $(≪-{hbox {30 dB}})$ performance, relaxed alignment tolerances $(pm hbox{20} mu{hbox {m}})$ and high-speed operation at a 10-Gb/s data rate are achieved. No degradation in the high-speed link performance is observed when offset input launches are employed. Moreover, a range of useful waveguide components that add functionality and enable complex on-board topologies are presented. The optical transmission characteristics of the fabricated components are investigated and it is shown that excellent performance is achieved. Excess losses as low as 0.01 dB per waveguide crossing, the lowest reported value for such components, and bending losses below 1 dB for 90-degree and S-shaped bends are obtained even with multimode fiber launches. Moreover, high-uniformity power splitting and low-loss signal combining are achieved with Y-shaped splitter/combiners while a variable splitting ratio between 30%–75% is demonstrated with the use of multimode couplers. Overall, the devices presented are attractive potential candidates for use in on-board optical links.