Low-loss single-mode GaAs/AlGaAs miniature optical waveguides withstraight and bending structures

Low-loss single-mode GaAs/AlGaAs miniature optical waveguides fabricated for use in monolithically integrated optical circuits are discussed. The propagation characteristics of these waveguides with straight and S-bending structures have been investigated at wavelengths of 1.30 and 1.55 μm. The lowest propagation losses are estimated to be 0.58 dB/cm and 0.69 dB/cm at wavelengths of 1.30 and 1.55 μm, respectively. The total loss of an S-bending waveguide with a curvature radius of 2 mm and with a lateral displacement of 200 μm was 0.61 dB and 0.46 dB at wavelengths of 1.30 and 1.55 μm. The fabricated single-mode strip-loaded waveguides proved to be suitable for application of the semiconductor waveguide into monolithically integrated optical circuits     

Stress-induced polymer waveguides operating at both 1.31 and 1.55 /spl mu/m wavelengths

Metal-defined polymer optical waveguides have been demonstrated for the first time. A metal strip patterned on top of a polymer slab waveguide causes a stress-induced refractive index change, providing lateral optical mode confinement within the core layer. Fabricated waveguides exhibit low propagation loss values of 1.1 dB/cm at 1.31 /spl mu/m and 1.3 dB/cm at 1.55 /spl mu/m for both TE and TM polarisations.     

Polymer-Based Long-Range Surface Plasmon Polariton Waveguides for 10-Gbps Optical Signal Transmission Applications

We present characteristics of very thin Au strip waveguides based on long-range surface plasmon polaritons (LR-SPPs) along thin Au strips embedded in polymers. We also report a 10 Gbps optical signal transmission via LR-SPPs with the pig-tailed Au strip waveguide at a telecommunication wavelength of 1.55 mum. We limited the thickness, width, and length up to ~20 nm, ~ 10 mum, and ~5 cm, respectively, for practical applications. At 1.55 mum, loss properties of the Au strip waveguides were theoretically and experimentally evaluated with thickness, width and cladding material. The lowest propagation loss of ~1.4 dB/cm was experimentally obtained with the 14-nm-thick and 2-mum-wide Au strip. With a single-mode fiber, the lowest coupling loss of less than 0.1 dB/facet was achieved with the 14-nm-thick and 7.5-mum-wide Au strip. The lowest insertion loss was obtained 7.7 dB with the 14-nm-thick, 5-mum-wide, and 1.5-cm-long Au strip. The propagation loss was improved approximately 30% for the 17-nm-thick Au strip with lowering the refractive index of the cladding polymer by 0.01. In the 10 Gbps optical signal transmission experiment, the LR-SPP waveguide exhibits an excellent eye opening and a 2.2 dB power penalty at 10^-12 bit error rate. These all results indicate that the LR-SPP waveguide is a potential transmission line for optical interconnects to overcome inherent problems in electric interconnects.     

Minimum-mode-size low-loss Ti: LiNbO3channel waveguides for efficient modulator operation at 1.3 µm

Efficient operation of Ti-diffused LiNbO3modulators and switches requires small, tightly guiding channel waveguide modes which effectively overlap the applied modulating field. This in turn requires Ti:LiNbO3channel waveguides with minimum mode size. The small-mode-size waveguides are obtained inz-cut crystals by optimizing the fabrication parameters to achieve maximum index change in the wave-guiding region and the optimum diffusion depth and width. For 6 h diffusion at 1025°C, and Ti strip thickness of 800 Å and strip width of 4 μm, the TM mode has a1/eintensity full width of 3.9 μm and full depth of 2.8 μm. This is by far the smallest mode size atlambda = 1.32 mum presented to date for Ti:LiNbO3waveguides. Since these waveguides have small mode size, largeDelta n, and low propagation loss (0.2 dB/cm) atlambda = 1.32 mum, it should be possible to fabricate modulators and switches with small voltage-length products and optical circuits that incorporate small bending radii curves, thus decreasing the total device length.     

10 Gbps Optical Signal Transmission via Long‐Range Surface Plasmon Polariton Waveguide

We demonstrate 10 Gbps optical signal transmission via long‐range surface plasmon polaritons (LR‐SPPs) in a very thin metal strip‐guided geometry. The LR‐SPP waveguide was fabricated as a 14 nm thick, 2.5 μm wide, and 4 cm long gold strip embedded in a polymer and pigtailed with single‐mode fibers. The total insertion loss of 16 dB was achieved at a wavelength of 1.55 μm as a carrier wave. In a 10 Gbps optical signal transmission experiment, the LR‐SPP waveguide exhibits an excellent eye opening and a 2.2 dB power penalty at 10^?12 bit error rate. We confirm, for the first time, that LR‐SPPs can efficiently transfer data signals as well as the carrier light.     

Fabrication of polymeric large-core waveguides for opticalinterconnects using a rubber molding process

Polymeric large-core (47 μm×41 μm) optical waveguides for optical interconnects have been fabricated by using a rubber molding process. For low-cost low-loss large-core waveguides, our newly developed thick-photoresist patterning process is used for a master fabrication. Also a low-loss thermocurable polymer, perfluorocyclobutane (PFCB), is used in fabricating optical waveguides by rubber molding for the first time. The propagation loss is measured to be 0.4 dB/cm at the wavelength of 1.3 μm, and 0.7 dB/cm at the wavelength of 1.55 μm     

Passive integrated-optical waveguide structures by Ge-diffusion insilicon

The realization of low loss optical channel waveguides and passive waveguide structures by a germanium indiffusion process into silicon will be discussed. Employing relatively simple technological processing like standard lithography, e-beam evaporation and diffusion, single-mode waveguides could be produced exhibiting polarization independent losses of as low as 0.3 dB/cm at wavelengths of λ=1.3 μm and λ=1.55 μm. S-bends fabricated with the same technology offered an excess loss of 1 dB at a radius of around 5 mm without any optimization. For a Y-junction designed with S-bends the maximum opening angle was determined to be 1.8° if an excess loss of 1 dB is allowed. The examination of directional couplers with various coupling lengths and distances revealed an excellent agreement between measurement and theory     

Fluorinated polyimide waveguides with low polarization-dependentloss and their applications to thermooptic switches

Fluorinated polyimide waveguides with low polarization dependent loss (PDL) and thermooptic (TO) switches made from them were demonstrated. The waveguides showed loss of less than 0.3 dB/cm at the wavelength of 1.3 μm and 0.6 dB/cm at 1.55 μm for both TE and TM polarizations. The PDL's were less than 0.1 dB/cm. Extinction ratios of Y-branching-type TO switches fabricated from these waveguides were larger than 20 dB when over 160 mW of electric power was applied at 1.3 μm, and over 150 mW at 1.55 μm. The switching speed was faster than 8 ms     

Silicon raised strip waveguides based on silicon and silicon dioxide thermal bonding

Si raised strip waveguides on SiO/sub 2/ have been proposed and fabricated, which are based on silicon-on-insulator (SOI) material. In the waveguides, the SOI technique utilizes silicon and silicon dioxide thermal bonding and back-polishing. An anisotropic etchant is used to produce the trapezoidal Si raised strip waveguides by etching the Si film down to the SiO/sub 2/ etch-stop buried layer. The transmission losses of the Si waveguides are measured to be less than 0.2 dB/cm at the 1.3 /spl mu/m wavelength for the lowest mode TE-like mode.     

PLZT film waveguide Mach-Zehnder electrooptic modulator

We report the numerical analysis and the fabrication of a reversed-ridge PLZT film waveguide. It is single-mode, has low transmission loss, and has large transverse cross-section suitable for efficient coupling to single-mode optical fibers. We used this structure to fabricate Mach-Zehnder (MZ) waveguide modulators. The field distribution in the channel and Y branch waveguides was calculated using a beam propagation method to analyze the modal profiles and the propagation loss. The reversed-ridge waveguides and the MZ structures were fabricated on r-sapphire substrates with a patterned ITO spacer film by sol-gel deposition. At 1.55 μm the propagation loss was 2.7 dB/cm. In the MZ, the half-wave modulation voltage was 8.5 V using 1.55 μm light and electrode length of 3.5 mm     

Si基槽型光波导的传输特性分析和传输损耗的测量

对Si基槽型(slot)光波导的传输特性进行了研究。 采用三 维时域有限差分(3D-FDTD)法研究了芯层中的光功率与波导槽型宽度及Si条带宽度之间的关 系,结果显示,槽型光波导具有很好的光功率约束效率,可以达到30%以上; 分析了光功率的变化规律及其优化,综合考虑光功率和光功率密度确定波导结构参数,实现 最佳光功率分 布,横向光功率分布沿x轴方向具有很好的约束效果,沿y轴方向呈现高斯分布;分析了底部Si薄层对光 功率的影响,100nm的底部Si薄层使得芯层的光功率下降50%,减小 底部Si薄层厚度有利于光功率约束效 率的提高;采用电子束刻写(EBL)技术和等离子刻蚀(ICP)技术制备了Si基槽型光波导,实验 研究了其传输损耗,结果显示,槽型光波导具有较低的传输损耗,达到13.5dB/cm。     

Sol-gel glass waveguide and grating on silicon

This paper reports on the fabrication and characterization of hybrid organic-inorganic glass sol-gel slab and channel waveguides by ultraviolet light imprinting in thin films deposited by a one-step dip-coating process. The adjustment of chemical composition of the materials provides precise selection of refractive index from 1.48 to 1.52 at the wavelength of 632.8 mn. The refractive index of the waveguides at 1.55 μm is similar to that of optical fiber, thus reducing the reflection loss between the two to less than 0.01 dB. The effect of ultraviolet light exposure and heat treatment on waveguide refractive index is studied. Fabrication parameters to produce ridge waveguides are optimized to achieve very smooth side walls. Propagation losses in these waveguides are ~0.1 dB/cm. Single mode buried waveguides, at 1.55 μm wavelength, with circular mode profile are demonstrated     

0.15 dB/cm loss in Unibond SOI waveguides

The optical loss of Unibond waveguides is measured and reported for the first time, using grating couplers. At a wavelength of 1.3 μm, a loss of 0.15±0.05 dB/cm is obtained for TE polarisation. This allows good quality low loss integrated optical circuits to be fabricated at low cost     

Germanium-diffused waveguides in silicon for λ=1.3 μm andλ=1.55 μm with losses below 0.5 dB/cm

The authors present a simple technique for the fabrication of integrated optical channel waveguides that are prepared by indiffusion of an E-beam evaporated amorphous alloy of germanium and silicon into commercially available silicon with low dopant concentration, using only simple technological processes such as standard lithography, PVD, and diffusion. The waveguides are polarization independent and have waveguide losses as low as 0.3 dB/cm at wavelengths of λ=1.3 μm and λ=1.55 μm. The spot sizes are well suited for low-loss single-mode fiber device coupling, being on the order of a few microns in both horizontal and vertical directions     

Fabrication of single-mode polymeric optical waveguides bylaser-beam writing

A laser-beam writing system is developed for large-area optical waveguide fabrication. Single-mode embedded channel optical waveguides are successfully fabricated on both 4- and 8-in silicon substrates using deuterated fluoromethacrylate polymers by laser-beam writing in photoresist and dry etching. The propagation loss of the waveguides is as low as 0.1 dB/cm at 1.3 μm     

激光直写技术制备SiO2-TiO2条形光波导工艺研究

为了研究激光直写技术在光波导制备中的应用,采用波长为1.07μm的连续光纤激光器制备了硅基SiO2-TiO2条形光波导。探讨了激光直写技术制备条形光波导的原理,研究了激光参数对条形光波导宽度的影响,最后测试了光波导的通光模场以及光传输损耗。结果表明,条形光波导的宽度随着激光功率密度的增加而增大。当激光扫描速率在0.1mm/s~1mm/s范围内变化时,条形光波导的宽度随着激光扫描速率的增加而降低;高于1mm/s时对波导宽度无明显影响。在优化的工艺参数下,激光直写得到的条形波导的厚度约为0.4μm,宽度为120μm,整条波导非常均匀、准直性很好,对于1550nm波长的光呈多模传输,最小传输损耗为1.7dB/cm。     

Integration of an electrooptic polymer in an integrated opticscircuit on silicon

This paper presents the joining of active nonlinear polymer waveguides with passive silicon nitride waveguides (SiO₂-Si ₃N₄-SiO₂) to form an integrated Mach-Zehnder modulator with a lateral electrode configuration on a silicon substrate. Passive and active waveguides are based on a silicon-nitride-strip guiding structure. In the active waveguide a nonlinear polymer layer is used to obtain an index modulation via the electrooptic effect. Despite the silicon nitride strip based guiding structure, 63% of the energy of the fundamental mode is guided in the nonlinear polymer (provided by Flamel Technology, Venissieux, France). Poling with field strengths up to 75 V/μm applied to the lateral electrodes has been employed to orient the chromophores. A half wave voltage of 35 V has been measured for an electrooptic coefficient of 5.8 pm/V at a wavelength of 1.3 μm. Optical loss measurements have been done on polymer and passive waveguides. The best results have been 1.8 dB/cm for the active and 0.78 dB/cm for the passive waveguides leading to a total loss of 6 dB for a modulator with an interaction length of 2.5 cm. The coupling loss between a laser diode and the passive waveguide structure was measured to be at least 4.6 dB using a microscope objective and piezo-electric displacement elements. Stability tests under atmospheric conditions have shown a decrease of the electrooptic coefficient which might be due to the hygroscopic behavior of the active polymer. The bandwidth of the modulator has been determined to be 4 MHz     

Fabrication and Evaluation of Nano-Scale Optical Circuits Using Sol-Gel Materials With Photo-Induced Refractive Index Variation Characteristics

Nano-scale optical circuits with core thickness of ~ 230 nm and core width of ~ 1 mum were fabricated and evaluated, using the photo-induced refractive index variation sol-gel materials, whose refractive index gradually increases by UV light exposure and baking. Propagation loss of linear waveguides was 1.86 dB/cm for TE mode and 1.89 dB/cm for TM mode at 633 nm in wavelength, indicating that there were small polarization dependences of ~ 0.03 dB/cm. Spot sizes of guided beams along core width direction and along core thickness direction were, respectively, 0.6 and 0.3 mu m for both TE mode and TM mode. Bending loss of S-bending waveguides was reduced from 0.44 to 0.24 dB for TE mode with increasing the bending curvature radius from 5 to 60 mu m. Although the bending loss for TM mode was slightly higher than that for TE mode, the difference was less than 10%. Branching loss of Y-branching waveguides was reduced from 1.33 to 0.08 dB for TE mode, and from 1.34 to 0.12 dB for TM mode with decreasing the branching angle from 80deg to 20deg. From these results, it is concluded that the photo-induced refractive index variation sol-gel materials can realize miniaturized optical circuits with sizes of several tens of microns and guided beam confinement within a cross section area less than 1.0 mum² with small polarization dependences, indicating potential applications to intra-chip optical interconnects.     

Low-loss Ti:LiNbO3waveguide bends at λ = 1.3 µm

Low-loss waveguide bends are necessary for many proposed integrated optical circuits. The bend loss associated with anS-shaped transition connecting offset 6 μm wide titanium-indiffused lithium niobate strip waveguides has been measured as a function of transition length and initial Ti metal thickness for 1.3 μm wavelength. Losses as low as 0.2 ± 0.2 dB have been achieved for a transition between offset parallel waveguides with a 0.1 mm lateral and 3.25 mm longitudinal separation. The bend loss is shown to be strongly dependent on the mode confinement and less sensitive to the shape of the transition curve.     

基于SOI的2×2 MMI耦合器的设计

设计了一种可用于阵列波导光栅(AWG)解调集成微系统的绝缘体上硅(SOI)基2×2多模干涉(MMI)耦合器,用光束传播法(BPM)对MMI耦合器进行了模拟。耦合器输入/输出波导采用倒锥形,多模干涉区尺寸为6μm×57μm。在TE偏振中心波长为1.55μm时,器件附加损耗为0.46dB,不均匀性为0.06dB。在1.49～1.59μm波长范围内耦合器的附加损耗小于1.55dB。仿真结果表明所设计的2×2MMI耦合器体积小、附加损耗低、波长响应范围宽、分光均匀,符合片上集成系统的要求。