Electro-optically tunable wavelength demultiplexer using depressed index waveguides

A novel configuration of an integrated optical tunable wavelength demultiplexer with a stable channel spacing is proposed. The structure consists of a three-mode depressed index diffused waveguide with single-mode input and output waveguides. The refractive index depression has been designed using experimental data of double diffusion of MgO on Ti:LiNbO/sub 3/ waveguides. The BPM simulation of the structure supports the feasibility of the device and shows a good wavelength tunability.<>     

Low-loss fiber-matched low-temperature PECVD waveguides with small-core dimensions for optical communication systems

Plasma-enhanced chemical vapor deposition (PECVD) offers a simple way of fabricating (doped) silica layers on silicon. A new design of the waveguide core allows low-loss fiber matched waveguides with low birefringence without high-temperature annealing. The increased loss of doped plasma deposited silica due to hydrogen incorporation is overcome by reducing the core dimensions and increasing the refractive index contrast. The waveguides can easily be fabricated using standard PECVD technologies and resist masked reactive ion etching (RIE) etching. Integrated optical devices such as 1/spl times/8 power splitters, 1300/1550-nm wavelength multiplexers and thermooptical switches were successfully fabricated and tested.     

条形介质加载型表面等离子体波导传输特性的研究

采用二维时域有限差分(FDTD)法,分析对比了 介质-金属(IM)结构和金属-介质-金属(MIM) 结构波导对光波传输特性的影响,以及通过对IM结构的尺寸、折射率进行优化得到最佳传 输长度。数值 结果表明,IM结构波导能使光波传输距离更长。对IM波导结构研究发现,当介质层厚为 300nm,金属 层厚为200nm时,传输效果最佳。基于这个参数的IM结构,计算介质 层折射率对IM波导光传输特性的影响发现,介质层折射率为1.5时, 在模场约束较好的情况下,传输损耗降低,表面等离 子体波的传输长度最长。整体优化后的条型波导可以实现最大传输距离为37μm。这一设计和优化波导结构 参数的方法不仅拓宽了介质加载型表面等离子体激元(SPP)波导结构的理论基础,在纳米光 学集成器件研究上也具有一定的应用潜能。     

Low-loss, single-mode, organic polymer waveguides utilizingrefractive index tailoring

Low-loss, single-mode optical waveguides have been fabricated from photopolymerizable acrylic monomers. The material system consists of a low-index cladding resin and a high-index core resin. The two resins are miscible so that precise control over the refractive index can be obtained. This allows the fabrication of single-mode waveguides with specific cross-sectional dimensions. One advantage of this is the ability to fabricate waveguides with high coupling efficiencies to other devices such as optical fiber or semiconductor lasers. The materials adhere to a wide variety of substrates and exhibit average waveguide losses of 0.56 dB/cm at 1300 nm for single-mode waveguides. Details of the fabrication procedure, index of refraction tailoring technique, and waveguide loss data are presented     

Grating-assisted coupling of light between semiconductor and glasswaveguides

Floquet-Bloch theory is used to calculate the electromagnetic fields in a leaky-mode grating-assisted directional coupler (LM-GADC) fabricated with semiconductor and glass materials. One waveguide is made from semiconductor materials (refractive index ≈3.2) while the second is made from glass (refractive index ≈1.45). The coupling of light between the two waveguides is assisted by a grating fabricated at the interface of the glass and semiconductor materials. Unlike typical GADC structures where power is exchanged between two waveguides using bound modes, this semiconductor/glass combination couples power between two waveguides using a bound mode (confined to the semiconductor) and a leaky mode (associated with the glass). The characteristics of the LM-GADC are discussed. Such LM-GADC couplers are expected to have numerous applications in areas such as laser-fiber coupling, photonic integrated circuits, and on-chip optical clock distribution. Analyses indicate that simple LM-GADC's can couple over 40% of the optical power from one waveguide to another in distances less than 1.25 mm     

Analysis of Optical Signal Transmission Characteristics in AWG Multi/Demultiplexer with Electromagnetic Field Theory

Based on the electromagnetic field theory, the optical signal transmission characteristics in input/output waveguides, slab waveguides and arrayed waveguides of the arrayed waveguide grating (AWG) multi/demultiplexer are analyzed. The relationship between the physical parameters such as geometry sizes and relative refractive index in AWG multi/demultiplexer and the optical signal transmission characteristics are discussed. This theoretical study can be used for optimizing the design and improving the performance of the AWG multi/demultiplexer.     

Analysis of Optical Singal Transmission Characteristics in AWG Multi/Demultiplexer with Electromagnetic Field Theory

Based on the electromagnetic field theory,the optical signal transmission characteristics in input/output waveguides,slab waveguides and arrayed waveguides of the arrayed waveguide grating(AWG) multi/demultiplexer are analyzed.The relationship between the physical parameters such as geometry sizes and relative refractive index in AWG multi/demultiplexer and the optical signal transmission characteristics are discussed.This theoretical study can be used for optimizing the design and improving the performance of the AWG multi/demultiplexer.     

Silica-based circular cross-sectioned channel waveguides

A technique for fabricating silica channel waveguides with circular cross sections is presented. The geometrical mismatch between a square or rectangular waveguide and a regular optical fiber is therefore largely reduced. The fiber-waveguide-fiber coupling loss drops from 1.8 dB to 0.5 dB or less for step index multimode waveguides by applying this technique. The heat treatment applied in the waveguide rounding process also smooths the waveguide sidewalls and results in much lower propagation loss in the waveguides. Uniform Y splitters were fabricated to show the feasibility of using this technique to make integrated optical devices.<>     

Index-and-dimensional taper and its application to photonic devices

A mode-field-converting optical channel waveguide with tapered refractive index and cross-sectional dimensions is proposed. In this waveguide, both the refractive index and cross-sectional dimensions of a core are adiabatically varied along a propagation direction in such a way that the normalized frequency V of the waveguide may be kept constant. Since radiation loss caused by waveguide imperfections is strongly dependent on the V value, the waveguide has good mode-field-converting capability without causing high radiation loss. Layer thickness and index of a core of a silica waveguide were tapered by modulating a raw material gas flow in a flame hydrolysis deposition method, and a channel width taper was formed by a photolithographical technique. In order to confirm the usefulness, taper waveguides have been used (1) to achieve good field matching between a fiber and a guided-wave optical switch, and (2) to fabricate a fiber-compatible monolithic 32×32 star coupler in a small chip     

Polymer Optical Interconnects—A Scalable Large-Area Panel Processing Approach

A flexible approach to producing optical interconnects on 609.6$ast ,$609.6 mm large-area panels is demonstrated. Stepwise projection patterning from 101.6$ast ,$101.6 mm masks has generated optical waveguide patterns over the whole panel using large-area projection lithography equipment. The waveguide routing design allows optical waveguides on different 101.6$ast ,$101.6 mm tiles to be interconnected. Four different waveguide connecting geometries in the border region between tiles have been fabricated and tested. Multimode waveguides from inorganic-organic hybrid polymers (ORMOCER) (cross section:$le hbox 50~muhbox mast hbox 10~muhbox m$) with refractive index step between core and cladding$Delta n=hbox 0.01$were produced. The index step was adjusted by mixing two diffrent ORMOCER systems. The materials show good adhesion to numerous substrates, such as glass and silicon. Application concepts such as flexible manufacturing of optoelectrical hybrid backplanes with two-dimensional interconnect, a three-dimensional optical interconnect with optical vias, and a hybrid backplane with the optical interconnect in a strip-format on a separate plane right above the electrical plane are proposed. Promising new technologies are presented along with preliminary demonstrativ viability.     

Low‐Loss Compact Arrayed Waveguide Grating with Spot‐Size Converter Fabricated by a Shadow‐Mask Etching Technique

This paper describes a low‐loss, compact, 40‐channel arrayed waveguide grating (AWG) which utilizes a monolithically integrated spot‐size converter (SSC) for lowering the coupling loss between silica waveguides and standard single‐mode fibers. The SSC is a simple waveguide structure that is tapered in both the vertical and horizontal directions. The vertically tapered structure was realized using a shadow‐mask etching technique. By employing this technique, the fabricated, 40‐channel, 100 GHz‐spaced AWG with silica waveguides of 1.5% relative index‐contrast showed an insertion‐loss figure of 2.8 dB without degrading other optical performance.     

Scalar BPM analyses of TE and TM polarized fields in bent waveguides

We have applied the effective index method to reduce the two-dimensional (2-D) refractive index profile into the 1-D refractive index structure and modified the wave equations to obtain the paraxial wave equations. Then, transverse electric (TE) and transverse magnetic (TM) polarized fields in the curved single-mode planar waveguides are analyzed by using the scalar beam-propagation method (BPM) employing the finite-difference method with a slab structure. The bending loss in bent waveguides is analyzed for optical fields obtained from the BPM and comparisons are made between the loss for the waveguides with various radius of curvature and refractive index difference. The outward shift of the optical field, which is generated at the connection between a straight and a bent waveguide, is obtained from the results of calculation of location of the maximum optical intensity. The transition loss can be reduced by introducing an optimized inward offset at a straight-to-bend junction. The birefringence for TE and TM polarized fields in bent waveguides is calculated from the phase difference of the optical fields. The wavelength shift due to the birefringence of TE and TM polarized fields in bent waveguides is also calculated.     

A new method for producing graded index PMMA waveguides

We report a new method for producing graded index polymethyl methacrylate (PMMA) waveguides using optical densification by angled X-ray exposure. The resulting larger refractive index near the surface of the waveguide serves to better isolate the guided light from potentially absorbing or scattering substrates than in waveguides of constant refractive index. We calculate that a 65° angle exposure in 6-μm-thick planar PMMA waveguide shifts the peak of the fundamental mode profile ~0.5 μm away from the substrate. Consistent with this result, we measure a reduction in the propagation loss of PMMA planar waveguides on a Ni substrate from 1.5 dB/cm to 0.5 dB/cm after angle X-ray exposure     

Impedance boundary method of moments with extended boundaryconditions

An improved impedance boundary method of moments is proposed to accurately and efficiently determine the propagation characteristics of multilayer planar optical waveguides whose refractive index profiles contain large step index changes or a graded-index region combined with step index changes. Extended impedance boundary conditions are used in the impedance boundary method of moments to replace regions in the waveguide structure which have refractive index discontinuities. Two methods for determining the extended boundary conditions include the standard transfer matrix method and a procedure utilizing a cascaded transmission line representation with successive calculation of input impedances. Simulation results show significantly improved convergence rates in the determination of propagation constants     

电场辅助离子交换制备玻璃光波导

使用电场辅助离子交换和热离子交换技术在玻璃基片上制作了平板波导。实验结果表明,这两种方法制作的波导的有效折射率分布不同,电场辅助离子交换技术制作的波导有效折射率呈近似阶跃型分布,而热离子交换制作的波导有效折射率分布为渐变型。经数值计算发现,近似阶跃型折射率分布的波导对光场限制得更好,更适用于制作有源光器件和集成光器件。     

Index profiles of planar optical waveguides determined from the angular dependence of reflectivity

The relation between the refractive index distribution and the angular dependence of reflectivity is investigated for planar optical waveguides. Index distributions with rapid variations of the profile function can be determined from the angular dependence of the difference in reflectivityDeltaRbetween the waveguide and the substrate by means of numerical parameter optimization.DeltaRis measured with high precision using a simple lock-in technique. This nondestructive method for profile evaluation is appropriate in particular for monomode waveguides where other methods fall to apply. It is tested with He+-implanted fused silica and results obtained for several ion energies and doses demonstrate the practical use of this method.     

中红外4 μm波长下MgF2晶体脊形光波导的制备及特性研究（特邀）

为了研究离子与中红外晶体相互作用的机理,探索中红外晶体光波导的制备和性能,采用离子辐照技术结合精密金刚石刀切割,在MgF₂晶体材料中制备了深度17.5 μm、宽度14 μm的脊形光波导。采用SRIM软件模拟了C5+离子辐照MgF₂晶体的电子能量损伤和核能量损伤的过程,分析了波导的形成机理;模拟了波导的折射率变化,并对波导的近场模式进行了实验测量和理论模拟;采用热退火处理来降低波导的传输损耗,将传输损耗降低为0.4 dB/cm;微拉曼光谱证明离子辐照过程并未对MgF₂晶体波导区造成较大的晶格损伤。该工作表明,离子辐照技术结合划片机精密切割是一种十分成熟的脊形波导制备手段,制备的MgF₂晶体脊形光波导在中红外集成光学和光通讯领域具有广泛的应用前景。     

Calculation of the effective indices of a GaN/InxGa1−xN optical guiding structure

In this paper, the effective refractive index of a GaN/In_0.38Ga_0.62N optical step index optical guiding structure has been investigated. The used method permits to approximate a three-dimensional optical waveguide to an equivalent waveguide where the index profile to be determined will only depend on y and z co-ordinates.The III-nitrides semiconductor devices have not been used or even investigated in the integrated optics field in order to design optical waveguides. It has been found that there exists a very good optical confinement in this device, where the In_0.38Ga_0.62N is lattice matched to the GaN.     

弯曲光波导端面修饰的设计方法

光波导的弯曲损耗一直是集成光学中一个值得人们重视的问题,为有效地减小光波导弯曲损耗,弯曲光波导的设计成为集成光学波导设计中的一个重要内容.本文在弯曲光波导保形变换方法的基础上,应用几何光学分析方法给出了波导弯曲损耗产生的简洁的物理图像,从而深入地分析了弯曲损耗产生的根本原因,并由此提出了弯曲光波导端面修饰的设计方法.理论分析表明,与传统的弯曲的光波导设计相比,该种设计方法可以有效地减小导波的模式泄漏,从而减小波导弯曲损耗.尤其是在弯曲光波导曲率半径、材料折射率等参数被设定的情况下,该种设计方法成为一种有效的设计方法.     

玻璃波导有效折射率的原位测量（特邀）

飞秒激光直写玻璃波导是快速制备三维集成光子芯片的一种重要手段,波导有效折射率的准确测量对于设计光子器件意义重大。设计并制备了一种断臂马赫-曾德尔干涉仪（MZI）结构对玻璃波导有效折射率进行原位精密测量。激光在断线区域和波导内的有效折射率不同,在传输相同长度下产生一定的相位差,最终导致不同的干涉结果。对断臂MZI结构的相位干涉结果进行处理,得到激光直写玻璃波导的有效折射率为1.504+7.7×10?4。利用RSOFT软件光束传播算法对器件进行模拟仿真,仿真结果与实验吻合良好。该精确测量玻璃波导有效折射率的方法对于提升光子芯片设计与制造能力具有重要意义。