聚合物光波导的模场特性分析

用时域有限差分法(Finite Difference Time-Domain,FDTD)对电光聚合物脊形波导进行了模拟分析,通过改变脊形波导的结构参数(脊高、脊宽、脊高比)来观察波导内的模场分布特性、对模式数量的影响.获得了通过调整脊宽和脊高比等参数,设计单模电光聚合物脊形波导的条件.同时验证了采用FDTD数值算法可以比较精确地模拟计算光波导器件性能.     

基于稀释波导的InP衬底上高耦合效率、低偏振敏感度1.55μm波长光纤-波导耦合器

研究了一种用于边入射型探测器的InP基高效光纤-波导耦合器.它由10个周期的未掺杂120nm InP/80nm InGaAsP(1.05μm带隙)多层膜组成的稀释波导构成.采用半矢量三维束传播(BPM)方法以及中心差分格式,模拟了不同条件下的光纤-波导耦合效率,从而得到了最优耦合条件.对于TE偏振和TM偏振模,计算所得到的最高耦合效率分别为94%和92%.同时,计算表明,此类基于稀释波导的光纤-波导耦合器具有高偏振不敏感性,偏振敏感度低于0.1dB.     

基于稀释波导的InP衬底上高耦合效率、低偏振敏感度1.55μm波长光纤-波导耦合器

研究了一种用于边入射型探测器的InP基高效光纤-波导耦合器.它由10个周期的未掺杂120nm InP/80nm InGaAsP(1.05μm带隙)多层膜组成的稀释波导构成.采用半矢量三维束传播(BPM)方法以及中心差分格式,模拟了不同条件下的光纤-波导耦合效率,从而得到了最优耦合条件.对于TE偏振和TM偏振模,计算所得到的最高耦合效率分别为94%和92%.同时,计算表明,此类基于稀释波导的光纤-波导耦合器具有高偏振不敏感性,偏振敏感度低于0.1dB.     

在InGaAsP/InP双异质结构中的光弹效应及其对侧向光的限制作用

从理论上计算了厚度为110nm的W0.95Ni0.05金属薄膜应变条在InGaAsP/InP双异质结构中形成的应力场分布,及由应力场分布引起的折射率变化.在W0.95Ni0.05金属薄膜应变条下半导体中0.2-2μm深度范围内,由应变引起条形波导轴中央的介电常数ε相应增加2.3×10-1-2.2×10-2(2μm应变条宽)和1.2×10-1-4.1×10-2(4μm应变条宽).同时,测量了由W0.95Ni0.05金属薄膜应变条所形成的InGaAsP/InP双异质结光弹效应波导结构导波的近场光模分布.从理论计算和实验结果两方面证实了InGaAsP/InP双异质结光弹效应波导结构对侧向光具有良好的限制作用.     

光纤耦合周期极化铌酸锂薄膜波导器件的研究

对硅基周期极化铌酸锂(PPLN)薄膜脊形波导进行了理论分析，并使用有限元软件模拟了25℃下泵浦波长为1560 nm的PPLN脊形波导的准相位匹配(QPM)周期与波导脊高和脊宽的关系。仿真结果表明，在相同脊宽(10μm)或脊高(10μm)下，PPLN脊形波导的QPM周期随着脊高或脊宽的增加而增大，最后趋于常数(即块状PPLN的QPM周期)。进一步模拟了在脊高和脊宽维持不变的情况下，PPLN脊形波导的QPM周期与温度之间的关系。结果表明，随着温度的增加，PPLN脊形波导的QPM周期逐渐减小，并且温度每升高1℃，QPM周期减小约3 nm。根据仿真结果制作了硅基片上集成PPLN脊形波导器件，将其封装成小体积的光纤入光纤出的波导，并测试了性能。当温度为24.8℃、1560 nm基频光输入功率为1.2 W时，最大输出653 m W的倍频光，光光转换效率达54.4%，归一化转换效率为20.2%·W^-1·cm^-2。     

PMMA脊形光波导的设计与场分析

利用有效折射率法（EIM）理论设计了有机聚合物脊形光波导结构,并分析光波导中传输的模式场,确定出光波导结构的适宜尺寸范围。光波导结构中分别选用PMMA（聚甲基丙烯酸甲酯）与PDMS（聚二甲基硅氧烷）作为波导层与包层的材料,用光漂白法来实现脊形波导结构。首先利用EIM法分析脊形波导区的宽度与高度之间的关系对归一化色散曲线的影响,以及波导层与包层的折射率匹配的影响,然后又通过分析波导区传输的基模场来讨论传输的损耗问题。研究发现波导结构的脊宽与脊高之比w／d越大,其有效折射率neff越大,而此结构尺寸又需约束在一定范围内,否则将造成很大的传输损耗。     

5层金属包覆介质波导的模式特性研究

采用有限元方法(FEM)对具有复折射率的金属包覆5层平板波导和矩形波导的折射率及模场分布进行了求解并进行了定性的分析。得到了5层平板波导的模折射率随芯层厚度、缓冲层厚度和金属层厚度的变化关系;给出了等离子体表面模的模场分布演变,揭示了在缓冲层变化时等离子体表面波向普通TM模式及低阶TM模向高阶TM模的演变过程：计算了二维结构5层矩形波导的模折射率随缓冲层厚度、芯层厚度和芯层宽的变化关系。结果表明,在二维结构的金属包覆波导中存在多种等离子体表面模,在缓冲层的变化过程中其TM模同样存在模式转变过程。并给出了部分等离子体表面模的模场分布;在金属层的影响下,TM模式的模场分布受到扰动,并给出了受扰动的低阶TM模的模场分布。     

SiON对Si基SiO2 AWG偏振补偿的数值分析

采用全矢量交替方向隐含迭代方法系统分析了高折射率SiON薄膜对Si基SiO2阵列波导光栅中波导应力双折射的影响.分析结果表明在芯区上或下表面沉积SiON薄膜可以明显减小Si基SiO2阵列波导光栅(AWG)中波导的应力双折射,但这两种补偿方法容易使模场偏移中心位置,不利于波导与光纤的耦合.理想的补偿方法是在芯区上下同时补偿,可减小模场偏移,并用该方法设计了偏振无关的16通道AWG.     

SiON对Si基SiO_2AWG偏振补偿的数值分析

采用全矢量交替方向隐含迭代方法系统分析了高折射率 Si ON薄膜对 Si基 Si O2 阵列波导光栅中波导应力双折射的影响 .分析结果表明在芯区上或下表面沉积 Si ON薄膜可以明显减小 Si基 Si O2 阵列波导光栅 (AWG)中波导的应力双折射 ,但这两种补偿方法容易使模场偏移中心位置 ,不利于波导与光纤的耦合 .理想的补偿方法是在芯区上下同时补偿 ,可减小模场偏移 ,并用该方法设计了偏振无关的 1 6通道 AWG.     

SiON对Si基SiO2 AWG偏振补偿的数值分析

采用全矢量交替方向隐含迭代方法系统分析了高折射率SiON薄膜对Si基SiO2阵列波导光栅中波导应力双折射的影响.分析结果表明在芯区上或下表面沉积SiON薄膜可以明显减小Si基SiO2阵列波导光栅(AWG)中波导的应力双折射,但这两种补偿方法容易使模场偏移中心位置,不利于波导与光纤的耦合.理想的补偿方法是在芯区上下同时补偿,可减小模场偏移,并用该方法设计了偏振无关的16通道AWG.     

InGaAsP/InP Buried‐Ridge Waveguide Laser with Improved Lateral Single‐Mode Property

A novel InGaAsP/InP buried‐ridg waveguide laser diode structure is proposed and demonstrated for use as a single‐mode laser. The lateral mode of the proposed device can be controlled by adjusting the composition and thickness of the InGaAsP layer grown over the active region. Stable single‐mode operation without kinks or beam‐steering is achieved successfully with lateral and transverse in the junction plane even for the device with the ridge width of 9 μm up to an injection current of 500 mA.     

Vectorial simulation of passive TE/TM mode converter devices on InP

Accurate calculations of polarization rotation at abrupt waveguide interfaces are performed by a vectorial two-dimensional finite difference scheme. It is shown that the small orthogonal component of the vector field in rib waveguides can play an important role in mode polarization rotation. Polarization rotations in mode converters fabricated on InGaAsP/InP by periodically arranged tilted waveguides or periodic loading of the rib are explained by these calculations, and design rules for passive mode converter devices are given     

Quasi planar spot-size transformer for efficient coupling between acleaved fibre and an InP/InGaAsP rib waveguide

A spot-size transformer structure is proposed for InP/InGaAsP double-heterostructure (DH) rib waveguide. Vertical expansion of a factor of 7 is achieved with 3 dB internal loss. Coupling from standard cleaved fibre (11 μm diameter mode) to a DH rib waveguide (5.8×0.8 μm large mode), is achieved with 4.5 dB polarisation independent loss. Coupling tolerances are highly relaxed. The fabrication method uses a thin cladding layer which ends up to a quasi-planar structure suitable with further integration process     

An optimized InGaAsP/InP polarization converter employing asymmetric rib waveguides

In this paper, we report on the design of a compact (/spl ap/ 226 /spl mu/m) on-chip InGaAsP/InP polarization converter based on an asymmetric rib waveguide. Our theoretical analysis demonstrates that the device displays a conversion efficiency of < -25 dB (> 99.68% power conversion between orthogonal polarization) at 1550-nm wavelength with a nearly flat response over the optical C band. Regarding fabrication tolerances, we predict that the most sensitive design parameter is the waveguide width as the conversion efficiency drops to 10 dB for a deviation of /spl plusmn/ 0.1 /spl mu/m from the optimized value.     

Single-mode and polarization-independent silicon-on-insulator waveguides with small cross section

The fabrication restrictions that must be imposed on the geometry of optical waveguides to make them behave as single-mode devices are well known for relatively large waveguides, with shallow etch depth. However, the restrictions for small waveguides (/spl sim/1 /spl mu/m or less in cross section) are not well understood. Furthermore, it is usually a requirement that these waveguides are polarization independent, which further complicates the issues. This paper reports on the simulations of the conditions for both single-mode behavior and polarization independence, for small and deeply etched silicon-on-insulator (SOI) waveguides. The aim is to satisfy both conditions simultaneously. The results show that at larger waveguide widths, waveguide etch depth has little effect on the mode birefringence because the transverse-electric (TE) mode (horizontal-polarized mode) is well confined under the rib region. However, at smaller rib widths, the etch depth has a large influence on birefringence. An approximate equation relating the rib-waveguide width and etch depth to obtain polarization-independent operation is derived. It is possible to achieve single-mode operation at both polarizations while maintaining polarization independence for each of the waveguide heights used in this paper but may be difficult for other dimensions. For example, a 1-/spl mu/m SOI rib waveguide with an etch depth of 0.64 /spl mu/m and rib width of 0.52 /spl mu/m is predicted to exhibit such characteristics.     

Simulation of Tunable Power Multimode Interference Couplers with Deep Rib Structure

The muhimode interference （MMI） couplers, which operate at 1. 55 microns in deep rib InGaAsP/InP waveguide with large lateral confinement and tunable power splitting ratios, are of high interest in integrated optics. The gold contacts are applied on the top of waveguides where tuning is desired and the plasma effect will lead to negative refractive index change. The three-dimensional （3D） finite difference beam propagation method（FD-BPM） is used to model the tunable MMI couplers. The length of a 2 × 2 overlap-MMI is determined by FD-BPM, so the longitudinal position of tuning spots is obtained. The position of gold contacts with two types, the edge-pads or center-pad, are also determined. In our design, the length of MMI is 180 microns. If the width of pads is 50 microns and the refractive index is tuned from 0 to -0. 027, the power ratio is tuned from 50 ： 50 to the maximum 88.5 ： 11.4. For deep rib structure, the effective index（EI） method can not be used to simplify the 3D waveguide to plane waveguide because of its lower precision, and so the direct 3D FD-BPM simulation is necessary for the design of 3D MMI couplers.     

A Single Etch-Step Fabrication-Tolerant Polarization Splitter

A tolerant single etch-step passive polarization splitter on InP/InGaAsP is designed and fabricated. The device consists of a directional coupler with a wide and a narrow waveguide. Modal birefringence of the third-order modes for transverse electric (TE) and transverse magnetic (TM) polarizations is employed to selectively couple one polarization. Tapering is applied to increase the tolerances. The devices are characterized, and the measurement results show good agreement with the beam- propagation-method simulations: a splitting ratio larger than 95% for a width range of around 100 nm and over a large wavelength range, covering at least the C-band.     

Stress-Induced Birefringence Characteristics of Polymer Optical Rib Waveguides

We report the detailed numerical investigation of stress-induced material birefringence in polymer rib waveguide for the design of nonbirefringent waveguide devices. To accurately simulate the stress-induced effects we propose a more realistic model in the finite element analysis which considers the stresses induced over the entire sequential fabrication process. It is observed that the birefringence is nonuniform, and it is different for different etch depth and core width. The maximum birefringence in the core layer is observed near the lower cladding which decreases to zero toward the top surface. The influence of this material anisotropy on the modal birefringence is analyzed also for different rib structures. We found the stress effects on the modal birefringence to be largely affected by etch depth, while core width has small effect. It is also found that the deeply etched core has better birefringence stability. Finally, an accurate design of the zero-birefringence waveguide is illustrated by taking the stress effects into account, and the results are compared with experimental data. Excellent agreement between calculated and experimental results confirms the potential application of this work to aid in the design of polarization-insensitive waveguide devices.     

Oscillation characteristics in InGaAsP/InP DH lasers with self-aligned structure

This paper presents new stripe geometry InGaAsP/InP DH lasers having mechanisms for suppressing current spreads and for controlling the transverse mode parallel to the junction plane. The theoretical study for optimum design of these lasers from which the analytic method of oscillation characteristics, including control of the transverse mode parallel to the junction plane attributable to refractive index and gain, was derived is discussed. The oscillation characteristics, especially the waveguide properties of the transverse mode are reported. Experimental results show excellent agreement with the theory and show that the transverse mode is totally confined by the built-in passive waveguide for a stripe width of 5 μm.