Mode-order converter in a multimode waveguide

A novel device that converts the order of modes in an integrated-optic multimode waveguide was proposed and fabricated. The device consists of two mode splitters and tapered waveguides. Its operation at a wavelength of 1.55 microm was confirmed by observation of the output mode profiles. The cross talk measured by an indirect method was >10.2 dB. The excess loss with reference to a straight multimode waveguide was 1.5 dB, compared with the propagation loss of a straight multimode waveguide.     

Waveguide mode converter based on two-dimensional photonic crystals

We propose and numerically analyze a novel mode converter based on two-dimensional photonic crystal waveguides with square arrays of cylindrical dielectric rods in air. The mode converter uses small perturbation defects to decouple various modes in the multimode waveguide, thereby permitting propagation of only one mode at any given frequency, which permits one-to-one mode conversion without exciting unwanted modes. The mode converter can efficiently convert a TM0 mode supported in a single-mode photonic crystal waveguide into a TM2 mode supported in the multimode waveguide that is laterally coupled to the single-mode waveguide section for a wide wavelength range. Influences of different sizes and positions of perturbation rods on the band structure of the multimode waveguide are studied.     

基于自映像的光子晶体波导分束器的设计

通过研究2维正方晶格光子晶体波导多模干涉的自映像效应,优化设计了一种新型1×2光子晶体波导分束器,采用时域有限差分法对其传输特性进行模拟分析。设计过程中,根据多模干涉耦合区中周期出现的双重像的位置确定两个单模输出波导的位置,通过在分束器输入和输出耦合区的连结处设置介质柱,改变输入和输出耦合区中的模场分布,实现模式匹配,从而明显减小分束器的反射损耗。计算结果表明:设置的介质柱归一化半径分别为0.08和0.177时,对于波长为1.55μm的入射光,该分束器的透射率可高达93%。     

Analysis of multiple reflections in hybrid photonic crystal multimode interference coupler

In this paper the analysis of multiple reflections in photonic crystal (PhC) multimode interference (MMI) couplers using eigen-mode expansion method is presented. The analysis is conducted on a hybrid PhC structure which consisted of 1-D PhC multimode waveguide sandwiched between 2-D PhC input/output waveguides. In PhC multimode waveguide, where the mechanism of wave confinement is not due to total internal reflection but due to photonic bandgap properties, the reflectivity at 2-D PhC facet wall would be very large for all the guided modes in the waveguide when ever the image formed due to MMI effect does not coincides with the output access waveguide.     

Optical Wavelength Filter Using Mode Conversion in Multimode Waveguide

A wavelength filter with simple structure using multimode waveguide is proposed . The device uses mode conversion by a grating structure fabricated simultaneously with the multimode waveguide.     

Subwavelength focusing and imaging by a multimode optical waveguide

A simple subwavelength focusing system formed by a straight or bent multimode waveguide is investigated numerically. The simulation results indicate that an appropriately designed multimode waveguide can focus the outgoing waves of a point source and form an image with a full width at half-maximum of less than half a wavelength in the near-field area at the other side of the waveguide. The physical mechanism of the subwavelength focusing for this imaging system is explained.     

8-信道MMI阵列波导光栅复用/解复用器的研制

本文首先详细分析了基于自镜象效应的MMIDMUX器件的基本工作原理,在此基础上,在GaAs/GaAlAs系材料上完成了对8信道MMIDMUX的具体设计.该器件的输入、输出单模波导和SIE多模波导采用离散谱折射率法进行优化设计,最后获得了当输入、输出单模波导宽度为3μm、SIE多模波导宽度和长度分别为40μm和1731.45μm时,该器件对8信道波长的隔离度为～26dB,理论传输损耗为～0.24dB.     

Modal properties of all-active InGaAsP/InP microring lasers

An experimental investigation of the multimode dynamics of 1.55 μm-InGaAsP/InP microring lasers is demonstrated. Different operation regimes are observed, bidirectional multimode, unidirectional single mode, bidirectional single mode and mode-hopping. The extent of each of the above operation regimes is examined with respect to the ring current level, bus waveguide reflectivity and ring radius. The back-reflections generated from the bus waveguide facets are indirectly controlled via the bus waveguide current. In order to clarify the physical mechanisms beyond experimental results, a multimode model based on the rate equation approximation is utilized. The experimental results are in good agreement to those predicted by the multimode model.     

Low-loss multimode waveguides crossings and turning mirrors

We develop a new design that the perturbation is the minimum when the crossing occurs at the self- image location in a low-loss multimode waveguide. We use a center-fold low-loss multimode waveguide with a single self image at the center. Such waveguides can cross at 90 degrees or 60 degrees at the center with minimal cross talk. One can reflect the incident mode into an intersecting waveguide by introducing an idea reflecting plane. In practice, the reflector is replaced by a plane for total internal reflection with correction for Goos-Hanchen shift.     

Design and optimization of novel ultra-compact SOI multimode interference optical switch

In this paper, an ultra-compact 3 × 3 SOI multimode interference optical switch is presented. There is only one hyperbolic multimode waveguide in the switch. By changing the refractive index of one or two parts within the hyperbolic multimode waveguide, the switch can realize on and off functions between any pair of input and output ports. The various states of the switch were simulated and analyzed using the finite difference beam propagation method (FD-BPM), the structure parameters of the switch were also designed and optimized. The optimized switch has excellent properties and the whole size of the switch is less than 4 mm.     

Design of novel three port optical gates scheme for the integration of large optical cavity electroabsorption modulators and evanescently-coupled photodiodes

This paper presents a novel scheme to monolithically integrate an evanescently-coupled uni-travelling carrier photodiode with a planar short multimode waveguide structure and a large optical cavity electroabsorption modulator based on a multimode waveguide structure. By simulation, both electroabsorption modulator and photodiode show excellent optical performances. The device can be fabricated with conventional photolithography, reactive ion etching, and chemical wet etching.     

SOI通道转换型多模干涉耦合器的研究

设计和制作了基于SOI的通道转换型多模干涉耦合器。用二维BPM方法分析了耦合器的性能与多模波导宽度和长度的依赖关系.制作出的耦合器能实现良好的通道转换,器件的功率转换比为73,附加损耗为2.2 dB.提高器件制作的精度将能进一步改善耦合器的性能.     

具有调制功能的多模干涉型1×3分束器

提出了利用量子约束斯塔克(Stark)效应制作具有调制功能的多模干涉型1×3分束器的设计思想,并详细分析了这种光分束器的工作原理。根据理论计算结果,制作了具有调制功能的多模干涉型1×3分束器。分束器的脊型多模波导长度为275μm,宽度为10μm,波导层采用GaAs/AlGaAs多量子阱结构,厚度约为0.2μm;电极采用共面波导结构。首先用有限差分光束传播法模拟了器件的光波传播特性,然后进行了初步的实验验证。理论模拟和实验结果表明,波长为0.86μm的高斯光束对称入射到多模波导的中心,器件实现了3分束功能;施加3 V的直流偏压,器件的调制深度达90%以上、调制带宽为2 GHz,实现了电吸收调制功能。     

扩展多模波导全内反射型Y分叉开关的分析

利用全内反射和波导理论，分析了多模波导反射区全内反射(Total Internal Reflection，TIR)型光开关的物理模型和降低串音和损耗的原因，给出改进Y分叉全内反射型光开关特征的近似计算方法。数值模拟表明，扩展多模波导的Y分叉全内反射开关的串音和损耗可分别下降15．5dB和0．65dB以上。     

Nondegenerate mirrorless oscillation in silicon waveguide

We propose nondegenerate four-wave mixing mirrorless oscillation in a multimode silicon nonlinear waveguide. Thanks to the large modal dispersion between two spatial modes caused by the high-index-contrast waveguide structure, two counterpropagating pumps of one spatial mode can generate two new optical waves of the other spatial mode at different frequencies. The phase-matching condition can be satisfied with the higher-order modes involved; therefore, frequencies of the newly generated light can be tuned by simply changing the pump frequency. The threshold power and conversion efficiency of the proposed mirrorless oscillation are investigated under different waveguide parameters.     

生物传感中平板光波导模式研究

为提高生物传感探测的灵敏度和响应速度,基于平面光波导理论,运用消逝场原理在生物传感领域的应用,在相同条件下比较了平面波导单模和多模2种模式下消逝场区域能量的大小,并且用VC和Matlab工具模拟论证单模能量高于多模。理论计算表明：单模和多模的荧光效率分别为5.83%和1.75%,在此计算中单模的荧光效率比多模的高。因此,在生物传感及其相关应用中,选用平板光波导的单模模式具有一定的优越性,为实际设计提供了理论依据。     

High-average-power Nd:YAG planar waveguide laser that is face pumped by 10 laser diode bars

A planar waveguide Nd:YAG laser is pumped with 430 W of power from 10 laser diode bars to produce a multimode output power of 150 W at an optical efficiency of 35%. Use of a hybrid resonator of the positive-branch confocal unstable type for the lateral axis and of one of the near-case I waveguide type for the transverse axis increased the laser brightness by a factor of ~26 with only 12% less power than in the multimode case.     

THz波段渐变波导中的多模传输特性

 根据耦合波理论,推导出轴对称渐变波导中, 考虑波导壁损耗时的多模传输时域耦合波方程组,并给出该方程组中各模式间耦合系数的具体表达式。据此编写了渐变波导中多模传输特性数值模拟程序。利用该程序计算了在THz波段圆波导中的模式衰减,在THz波段研究波导中的多模传输特性时,必须考虑波导壁的阻抗损耗影响。数值分析了直波导中的模式耦合问题,从而证实了波导壁有限电导率能产生模式耦合这一耦合机制。介绍了利用该程序数值分析波导耦合器和过渡器中多模传输特性的两个例子,利用该程序可对波导耦合器和过渡器中的多模传输特性进行数值模拟分析,进而对结构进行设计和优化。     

采用三维波束传输法的多模干涉耦合器成像位置的数值计算

多模干涉(MMI)耦合器需要精确定位成像位置,以便器件的设计制作。针对强限制和弱限制的三维多模波导干涉耦合器,采用三维交替方向隐式有限差分光束传输法(BPM),数值计算得出多模波导长度、输入波导和输出波导位置。首先通过对对称干涉多模干涉耦合器的数值分析求得多模干涉耦合器的等效宽度Weq及最低二阶模之间的拍长Lc,然后将这些参量结合光束传输法直接用于器件设计。计算显示该方法得到的成像位置和导模传输分析法(MPA)的理论预测比较接近,但Weq和Lc却是由光束传输法计算得到的,导模传输分析法理论只能在得到Weq和Lc的前提下才能得到成像位置。该方法直接针对三维波导进行,没有采用基于等效折射率方法的从三维波导到二维波导的简化处理,并且也没有采用导模传输分析法所采用的近似,保证了计算精度,对于实际多模干涉器件的设计制作可起参考作用。