New Criterion for Designing Silica Multimode Interference Power Splitters

We introduce a new criterion for designing 1 × N silica multimode interference power splitters using overlapping-image multimode interference analysis. This criterion requires that widths of multimode waveguides in the devices should be greater than 2 times the product of port number N and effective widths of output waveguides. Better device uniformity can be achieved when the new criterion is satisfied.     

Multimode Interference All-Optical Logic Gates via Partially Nonlinear Propagation Region

We propose a new structure containing multimode interference waveguides with partial nonlinear Kerr-like material whose function is like a phase shifter for all-optical logic gates. It has the advantages of compactness and insensitivity to relative phase difference between the incident beams. In this paper, we analyze the structure by finite difference time domain method and demonstrate such logic gates as AND, NOT and XOR logics.     

一种基于多模干涉耦合器的模转换与合并器件的设计

多模波导干涉（MMI）耦合器在集成光路中被用来实现波导模式的转换或合并。对于实际的基于硅绝缘体（SOI）的三维波导，数值设计方法是必需的。采用有限差分波束传输法（FD-BPM）设计了一种66％模式转换、合并器。首先由FD-BPM求出MMI耦合器的输入、输出波导所支持的基模和一阶导模的模场分布，通过数值方法得到MMI耦合器的长度，然后将求得的模场作为输入波场，经过FD-BPM运算后在器件输出面上计算交叉积分得出实际的由基模转换为一阶模的功率百分比。对于算例中采用的SOI波导，器件长度为829μm，65．7％的功率由基模转换为一阶模。     

Robust 2 × 2 Multimode Interference Optical Switch

A robust 2 × 2 photonic switch based on multimode interference (MMI) effects is proposed. We demonstrate that the device is very tolerant to material modifications and typical fabrication errors. This is a result of the MMI design and the high symmetry of the switch. The key parameter for the operation of the device is that the input light forms a pair of well defined self-images exactly in the middle of the switch. The index modulated regions precisely overlap the positions where these two self-images are formed. By creating identical contact features at these locations, any refractive index change induced in the material as a result of electrical isolation will be replicated in both self-images, and therefore the off-state output will not be altered. In the same way, offset and dimension errors are reflected symmetrically on both self-images and do not seriously affect the imaging. The characteristics of the switch under different scenarios are investigated using the finite difference beam propagation method. By employing this configuration, crosstalk levels better than −20 dB are achievable over a wavelength range of 100 nm while maintaining polarization independence.     

多模干涉耦合器一般成像位置分析

自映像效应是多模波导的一个重要特性,利用多模波导自映像效应制成的多模干涉耦合器被广泛地应用于集成光学回路中。然而根据以往的文献要得出多模干涉耦合器的成像位置要经过一系列复杂的计算。根据多模干涉耦合器的自映像原理,对多模干涉耦合器的成像位置进行分析。成像位置与输入场位置和位置数密切相关,给出了成像位置的解析表达式,得出奇数、偶数的位置数的成像位置分别对应相同,并且奇、偶数的位置数所对应的成像位置之和为多模波导宽度的成像规律。用导模传输分析法验证了表达式和成像规律的正确性。根据成像位置的表达式和成像规律可以直接得出任意输入场位置和位置数所对应的成像位置。为一维和二维限制的多模干涉耦合器的设计提供了理论基础。     

TLM Analysis of Multimode Interference Devices

In this article, the use of the transmission line matrix (TLM) method for the analysis of multimode interference (MMI) devices is demonstrated. Time domain solvers of Maxwell equations, such as the TLM method, are a highly accurate alternative in the modeling of photonic devices that permit overcoming the limitations found in other approximate methods. The full optical transfer function is obtained from the computation of the device response to a single input temporal pulse. A novel parallel computation scheme based on a sliding window wave propagator permits reduction of the high computational load requirements.     

Novel multimode interference devices for low index contrast materials systems featuring deeply etched air trenches

A novel design of multimode interference (MMI) device is proposed for photonic integrated circuits fabricated in low index contrast materials. In this design, deeply etched air trenches are used to define the boundaries of the multimode section to achieve strong lateral confinement. This results in superior imaging quality and therefore lower loss and imbalance, which can only be achieved in strongly guiding MMIs. However, the access waveguides remain weakly guiding, which is essential for low loss fibre connection. We demonstrate the merit of the design in 1 × 4 MMI power splitters. By introducing air trenches, loss decreases from 0.45 to 0.053 dB and imbalance decreases from 0.15 to 0.058 dB for TE polarization. For TM polarization, loss decreases from 0.46 to 0.003 dB and imbalance decreases from 0.16 to 0.067 dB.     

具有分光功能的电吸收调制器分析

利用有限差分光束传播法和导模传输分析法,对GaAs/AlGaAs多量子阱波导型电吸收调制器和多模干涉型分束器的光传播特性进行了理论分析,提出了制作具有分光功能的电吸收调制器的设想,并进行了模拟和实验验证.     

基于多模干涉耦合器的集成热光开关实验研究

报道了一种基于多模干涉(MMI)耦合器的马赫曾德尔干涉仪(MZI)型2×2集成热光开关的实验研究结果,插损为3.40 dB,偏振相关损耗为0.47 dB,直通和交叉状态消光比分别为32.01 dB和16.42 dB,响应时间小于3 ms,开关功耗为658 mW。针对直通和交叉状态消光比不对称的现象,从理论上做出了解释,因为半导体平面光波电路(PLC)工艺一致性较好,两个多模干涉耦合器的分光比虽然因工艺误差偏离50∶50,但误差量相近,这个特点对光开关直通和交叉状态的消光比产生了不同影响。分析了在波导上制作加热电极对波导有效折射率的影响,估算其增量在2×10-4量级。     

不同衬底折射率的多模干涉耦合器

设计了一种具有不同衬底折射率的新型多模干涉耦合器,在多模波导区引入了更强的光场限制,激发更高阶的导模,从而提高映像质量.采用二维有限差分波束传播方法模拟了这种新型的结构,结果表明:与传统结构相比,以功率均衡性和附加损耗为衡量标准的映像质量有了明显提高.这种结构可以应用于三维SOI脊形波导中.     

Design and optimisation of multimode 1D photonic band gap waveguide

The modal characteristics of planar waveguides with photonic band gap guiding properties are studied. It is demonstrated that a slight deviation from the periodicity in the photonic band gap multilayers can result in multimode transmission within the guiding layer. Possible applications of the results for avoiding single mode regime destruction due to fabrication process imperfection, as well as for designing such waveguides for conventional and emerging new applications of multimode photonic devices, are pointed out.     

Design and optimisation of multimode 1d photonic band gap waveguide

The modal characteristics of planar waveguides with photonic band gap guiding properties are studied. It is demonstrated that a slight deviation from the periodicity in the photonic band gap multilayers can result in multimode transmission within the guiding layer. Possible applications of the results for avoiding single mode regime destruction due to fabrication process imperfection, as well as for designing such waveguides for conventional and emerging new applications of multimode photonic devices, are pointed out.     

具有单一复合调制区的多模干涉效应耦合器1×3光开关的分析

基于多模干涉自映像原理，分析了一种仅含一个复合调制区的1×3光开关。该开关处于不同工作状态时，调制臂上所加相位调制量之间存在倍数关系，于是可将调制臂上的相移器组合成一个复合调制区，通过连续改变复合调制区的折射率变化量，因此可以将来自任一输入端的光场轮流切换到任意输出端口。以Al0.07，Ga0.93As／GaAs脊形波导结构为例，采用BEAMPROP软件，对该开关进行了优化和理论验证。消光比高达30．3dB；相邻通道之间的串扰低于-29．8dB；在1．31μm工作波长处约50nin的波谱范围内，串扰低于-20dB。该结构可简化传统多通道开关的调制方法，降低外加控制方法的复杂程度。     

Semi-vectorial analysis of a compact wavelength demultiplexer based on the tapered multimode interference coupler

Based on a parabolically tapered multimode interference (MMI) coupler with a deep-etched SiO₂/SiON rib waveguide, a compact wavelength demultiplexer operating at 1.30 and 1.55\mum wavelengths is proposed and analysed by using three-dimensional semi-vectorial finite-difference beam propagation method (3D-SV-FD-BPM). The results show that a MMI section of 330.0\mum in length, which is only 76% length of a straight MMI coupler, is achieved with the contrasts of 42.3 and 39.2dB in quasi-TE mode, and 38.4 and 37.8dB in quasi-TM mode at wavelengths 1.30 and 1.55\mum, respectively, and the insertion losses below 0.2dB at both wavelengths and in both polarization states. The alternating direction implicit algorithm with the Crank--Nicholson scheme is applied to the discretization of the 3D-SV-FD-BPM formulation along the longitudinal direction. Moreover, a modified FD scheme is constructed to approximate the resulting equations along the transverse directions, in which the discontinuities of the derivatives of magnetic field components H_y and H_x along the vertical and horizontal interfaces, respectively, are involved.     

一种多模干涉耦合器的性能模拟

为减小多模干涉（Multimode Interference ,MMI）耦合器件的尺寸,提出一种多模波导宽度为指数型变化的Taper结构.理论分析了多模波导长度与该Taper结构的参量之间的关系.与已被用于减小MMI器件尺寸的抛物线型Taper结构相比,该结构可进一步减小器件的尺寸.就几种波导结构参量下的MMI耦合器,利用宽角光束传播法进行了数值模拟.结果表明,指数型MMI耦合器的性能与抛物线型MMI耦合器的性能类似.指数型Taper结构可以用于MMI器件以减小该类器件的尺寸.     

双椭圆纳米金属棒构成的表面等离子体波导的传输特性分析

设计了一种双椭圆纳米金属棒表面等离子体波导,采用频域有限差分法,对这种波导所支持的基模的能流密度分布、有效折射率和传播长度随几何结构参数和工作波长的依赖关系进行了分析.结果表明,沿纵向的能流主要分布在两个椭圆金属棒所形成的中间区域,且越靠近金属棒的弧形边,沿纵向的能流越大.通过调节两个金属棒的中心距离以及它们的两个半轴的大小,可以调节模式的有效折射率和传播长度.在工作波长确定的条件下,相对于a=b的情形来说,在a<b时,场与金属表面接触的面积较大,场 关键词： 集成光学 光波导 表面等离子体波导     

基于三角晶格光子晶体多模波导1×2分束器的优化设计

依据自映像原理,设计了一种基于三角晶格光子晶体多模波导的1×2分束器.采用时域有限差分法模拟了光波在分束器中的传播行为,并计算了分束器的传输效率.结果表明,仅仅通过改变多模波导与输出波导联结处的介质柱的位置对结构进行优化,便可大大提高分束器在工作点频率处的传输效率和带宽,其多模耦合区的长度可低至3.1 μm.因而本文所设计的分束器具有更小的器件尺寸和更高的传输效率,易于大规模集成的实现,在未来的集成光路中具有广泛的应用价值.     

多模干涉耦合器中重叠像相干相消现象分析

根据多模干涉耦合器的自映像原理和重叠成像的规律, 首次提出多模干涉耦合器中存在重叠像相干相消现象, 推导了重叠像相干相消现象出现的条件. 在此基础上, 对对称干涉和成对干涉两种特殊重叠成像做出解释, 得出对称干涉和成对干涉成像个数及成像位置的表达式. 用实例证明了重叠像相干相消现象并不只存在于成对干涉和对称干涉两种特殊情况, 并总结了重叠像相干相消随位置数变化的规律. 用导模传输分析法验证了所得表达式和成像规律的正确性. 关键词： 集成光学 多模干涉耦合器 相干相消 导模传输分析法     

Full-vectorial analysis of optical waveguides by the finite difference method based on polynomial interpolation

Based on the polynomial interpolation, a new finite difference (FD) method in solving the full-vectorial guided-modes for step-index optical waveguides is proposed. The discontinuities of the normal components of the electric field across abrupt dielectric interfaces are considered in the absence of the limitations of scalar and semivectorial approximation, and the present FD scheme can be applied to both uniform and non-uniform mesh grids. The modal propagation constants and field distributions for buried rectangular waveguides and optical rib waveguides are presented. The hybrid nature of the vectorial modes is demonstrated and the singular behaviours of the minor field components in the corners are observed. Moreover, solutions are in good agreement with those published early, which tests the validity of the present approach.     

多模干涉马赫曾德尔光开关模型

根据N×N多模干涉耦合器的基本原理 ,确定了多模干涉耦合器的结构参数。通过分析多模干涉耦合器的输入光场与其映像间的相位关系 ,提出了模传输矩阵的分析方法 ,并用此方法分析了N×N普通干涉多模干涉耦合器、N×N相移器以及N×N普通干涉多模干涉马赫 曾德尔光开关 ,得到了它们的模场传输方程 ,分析了光开关在光场从任一输入端输入 ,从任一输出端输出时开关的驱动条件。用上面的方法分析了 4× 4光开关的结构及驱动条件