Analyzing the polarization dependence in optical spot-sizeconverter by using a semivectorial finite-element beam propagationmethod

This paper describes a semivectorial wide-angle finite-element beam propagation method (FE-BPM) that uses the Pade approximation and that can allow efficient and accurate analyzes of the polarization dependence in arbitrary step-index optical waveguide devices. It also reports the use of this method to analyze the polarization dependence of coupling loss between a semiconductor tapered-waveguide spot-size converter and a single-mode optical fiber. It is shown that semiconductor spot-size converters having cores with a small cross-section provide low-loss and polarization-insensitive coupling to flat-end fibers. A low-loss (far less than 1 dB) and completely polarization-insensitive spot-size converter can be made using a lightly n-doped InP substrate for the tapered waveguide. These spot-size converters are consequently potentially useful for making polarization-insensitive semiconductor optical devices such as optical amplifier gate switches     

有双包层结构的楔变脊型光斑转换器的设计

为了提高硅基上单模波导器件与单模光纤的耦合效率和工艺容差,设计了一种实用新型光斑转换器,它由水平和垂直双向楔变的波导芯区和双内包层构成.分析了内包层折射率与其厚度对耦合效率的影响,发现通过优化内包层的参数可以加强对扩展光场的限制.针对在硅基上制作垂直楔变结构的波导还很困难的情况,提出了一种低成本、简单可行的制作方法.     

有双包层结构的楔变脊型光斑转换器的设计

为了提高硅基上单模波导器件与单模光纤的耦合效率和工艺容差,设计了一种实用新型光斑转换器,它由水平和垂直双向楔变的波导芯区和双内包层构成.分析了内包层折射率与其厚度对耦合效率的影响,发现通过优化内包层的参数可以加强对扩展光场的限制.针对在硅基上制作垂直楔变结构的波导还很困难的情况,提出了一种低成本、简单可行的制作方法     

Spot-size converted polarization-insensitive SOA gate with avertical tapered submicrometer stripe structure

To develop polarization-insensitive semiconductor optical amplifier (SOA) gates into more efficient and functional optical components by using hybrid integration with a planer lightwave circuit (PLC) platform, vertical tapered spot-size converters were integrated into a SOA gate with a narrow mesa-stripe structure of submicrometer width leading to low coupling loss (2.6 dB). Very-low polarization dependence of gain (<0.2 dB) and high extinction ratio (>30 dB) were achieved in a wide wavelength range (40 nm). High-speed (<1 us) gate operation was also demonstrated. These results indicate that the spot-size converted SOA integrated on a PLC platform will perform well in wavelength-division-multiplexing (WDM) applications     

A simple laterally tapered waveguide for low-loss coupling tosingle-mode fibers

Low-loss coupling between semiconductor photonic devices and single-mode fibers is achieved using a simple InP/InGaAsP tapered waveguide. The proposed simple structure has a small and nearly square guiding core at its output facet. In this structure, the output field has a non-Gaussian profile, but low-pass filter coupling can be achieved by optimizing the design of the guiding core sizes. The waveguide is composed of a laterally tapered InGaAsP guiding layer and an InP cladding region on an InP substrate, facilitating integration of the waveguide with active devices using conventional processes. The waveguide is shown to have a total insertion loss of 2.6 dB, including a coupling loss of 0.9 dB and large ±2.5-μm misalignment tolerance in lateral and vertical directions with single-mode filters     

Large reduction of singlemode-fibre coupling loss in 1.5% Δplanar lightwave circuits using spot-size converters

Reduction of singlemode fibre coupling loss in 1.5% Δ planar lightwave circuits from 1.8 to 0.2 dB/point is achieved using simple vertically and laterally tapered spot-size converters. These spot-size converters were used to realise an arrayed-waveguide grating with a very low insertion loss of 0.7 dB     

Low-loss fibre-chip coupling by buried laterally tapered InP/InGaAsP waveguide structure

A passive InP/InGaAsP spot-size transformer for low-loss coupling of semiconductor optoelectronic devices to single-mode fibres has been fabricated entirely on InP. Using a buried two-layer laterally tapered section, spot-size transformation is demonstrated from below 2 mu m up to 8 mu m, the spot size of a dispersion-shifted fibre at 1550 nm. For a chip without antireflection coating a total insertion loss of 2.7 dB was achieved at a taper length of approximately 600 mu m.<>     

Design of a single-mode tapered waveguide for low-losschip-to-fiber coupling

The novel waveguide structures described in this paper have nonlinearly tapered shapes that result in low radiation losses despite their relatively short lengths. The core at the waveguide endface connected with the fiber has a very small cross section and an expanded mode field with a non-Gaussian shape. The taper structures are analyzed by using an improved step-transition method. This method is a based on the theory of enclosing a waveguide within electrical walls and that can therefore treat the radiation modes in a tapered waveguide as discrete mode spectra. Analyzing the relationships between the lengths and shapes of the tapers and the radiation loss due to the tapers show that appropriately tapered semiconductor waveguides operating at an optical wavelength of 1.55 μm and having a taper length of less than 0.7 mm can have a radiation loss of only 0.1 dB and a coupling loss with a conventional single-mode fiber of less than 0.5 dB     

硅基波导用楔形模斑变换器的研究进展

楔形模斑变换器在利用硅基光子集成技术实现芯片间光互连中有着广泛的应用.文章概述了国内外楔形模斑变换器的最新研究进展.介绍了几种新型模斑变换器的结构及制作的工艺流程,并对其性能及影响楔形模斑变换器耦合效率的几个因素进行了分析比较,进而讨论了这几种模斑变换器存在的问题及进一步提高耦合效率的可能性.     

High-gain array of semiconductor optical amplifier integrated withbent spot-size converter (BEND SS-SOA)

We propose a high-gain semiconductor optical amplifier with an integrated bent spot-size converter (BEND SS-SOA). A straight active waveguide enables us to use a pn-buried heterostructure (pn-BH) with a high current-blocking effect and uniform characteristics. We can optimize a bent spot-size converter waveguide to provide low optical feedback from the facets and high-coupling efficiency to a flat-end optical fiber with low radiation loss due to the bend. The devices we fabricated achieve a high fiber-to-fiber gain of 18 dB with a coupling efficiency of -3.5 dB, and we have demonstrated a four-channel array with uniform characteristics     

熔锥型单模光纤耦合器模型的优化研究

在弱导和弱耦合近似条件下,对光纤耦合器的几何形状做近似处理,并采用连续函数进行描述.根据Snyderd的局部模式理论,采用三角波与高斯波的变系数叠加函数对光纤耦合器纵向各区域的光模场分布进行描述.利用局部模耦合理论和变分法计算分析光纤耦合器纵向各区域的传播常数和耦合系数,讨论耦合系数与结构参数和波长的关系.计算表明:光纤耦合器熔锥区对光纤耦合器中的光功率耦合行为的影响不可忽略,光纤纤芯半径和包层半径对耦合区和熔锥区的耦合系数的影响成相反趋势.因此,可以通过合理控制耦合器的结构参数,制作出宽带平坦光纤耦合器.     

基于多谐振耦合的异质包层全固光子带隙光纤的研究进展

针对人们对特种光纤的不断增长需求,介绍了基于多谐振耦合机理的异质包层(HC)结构全固光子带隙光纤(AS-PBGF)的工作原理,以及该种结构光纤在实现大模场面积、单模运转和低弯曲损耗等特性的优势。从无源光纤和有源光纤角度分类,着重总结并分析了近些年国际上相关课题组对此种结构光纤的研究报道与进展。最后,展望了基于多谐振耦合机理的HC结构AS-PBGF的应用方向。     

Tapered single-mode optical fiber evanescent coupling

We describe the results of a numerical and experimental investigation of how a point source of radiation couples light to the HE ₁₁ mode of a tapered single-mode fiber. Specifically, we have investigated two different geometries of nonadiabatic, tapered single-mode optical fiber. The motivation for this study is the characterization of a single-mode tapered optical fiber biosensor. In such a device light is collected from fluorescent sources located along the cladding surface of the tapered fiber. Taper-to-taper coupling measurements and fiber mode calculations indicate the device sensitivity decreases exponentially as sources are moved away from the tip of the tapered fiber     

双包层手征光纤的色散特性

在对双包层手征光纤(W型)进行解析求解的基础上，用数值计算方法研究了纤芯和内外包层的手征参数和内包层厚度对模式色散特性的影响，给出了双包层手征光纤中基模的归一化传播常数b、群延迟d(Vb)／dV和波导色散Vd2(V6)／dV2随纤芯和内外包层的手征参数和内包层厚度的变化关系曲线。结果表明在双包层光纤的纤芯和内外包层中引入手征，可以极大地改变光纤中基模的色散特性，特别是内包层厚度不同时，色散特性也极为不同．     

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     

Angled-Facet Spot-Size-Converter Integrated Semiconductor Optical Amplifiers Using Asymmetric Twin Waveguide Technology

The extinction ratio (defined as the difference in the optical power between 0-dB fiber-to-fiber loss and the off state level) is enhanced with the introduction of an S-bend waveguide structure using asymmetric twin waveguide techniques for a spot-size converter integrated semiconductor optical amplifier (SSC-SOA) with a polarization-insensitive offset superlattice. Angled waveguides are introduced in order to obtain low facet reflectivity without the need for antireflection coating. A curved waveguide is introduced to connect the angled and straight waveguide, minimizing their coupling loss while achieving a lateral spatial mode filter. The SSC-SOA, operating at 1.62-mum wavelength, achieves an extinction ratio up to 70 dB and a fiber-to-fiber gain of 10 dB using cleaved, flat end single-mode optical fibers.     

1.55 micrometer ridge DFB laser integrated with a buried-ridge-stripe dual-core spot-size converter by quantum-well intermixing

A ridge distributed feedback laser monolithically integrated with a buried-ridge-stripe spot-size converter operating at 1.55 micrometre wavelength was successfully fabricated by means of low-energy ion implantation quantum-well intermixing and dual-core technologies. The passive waveguide was optically combined with a laterally exponentially tapered active core to control the mode size. The devices emit in a single transverse and single longitudinal mode with a sidemode suppression ratio of 38.0 dB. The threshold current was 25 mA. The beam divergence angles in the horizontal and vertical directions were as small as 8.0 degree X 12.6 degree, respectively, resulting in 3.0-dB coupling loss with a cleaved single-mode optical fiber.     

Coupling of modes in bent biconically tapered single-mode fibers

Biconically tapered single-mode fibers are fabricated by heating a single-mode fiber while applying tension. As a result of this tapering, cladding modes are excited in the tapered region of the fiber where the V parameter of the fiber goes down below 1.0. These cladding modes couple to one another, leading to fluctuations of the optical throughput. Since the index difference between the cladding and the external medium is rather high (~0.5), the cladding modes will be of the exact type, namely, TE, TM, HE, and EH modes. The coupling of these modes in the tapered region is analyzed using the exact mode formalism when the tapered region is bent. The theoretical results agree very well with experimental results obtained on bent tapers which show strong fluctuations of the optical power as a function of the bending angle     

使用传统工艺实现1.55μm激光器与模斑转换器的单片集成

采用传统的光刻和湿法腐蚀工艺制作了1.55μm波长的新型半导体激光器和模斑转换器的单片集成器件.其中激光器采用脊型双波导,模斑转换器采用掩埋双波导结构,水平楔型的有源波导和宽而薄的无源波导同时控制光斑模式大小.实验测得器件的阈值电流为40mA,斜率效率为0.35W/A,水平和垂直方向的远场发散角分别为14.89°和18.18°,与单模光纤的耦合损耗为3dB.     

Compact and low-loss arrayed waveguide grating module with tolerance-relaxed spot-size converter

A compact, low-loss arrayed waveguide grating (AWG) module was achieved by adopting a novel optical spot-size converter (SSC) to planar lightwave circuits (PLCs). The SSC is a laterally tapered waveguide that can be fabricated simply by the conventional fabrication process. The structure is composed of a core width converting region where the spot-size is converted efficiently, and a core width fine-tuning region where the cut-position tolerance is relaxed. We have applied this structure to a 1.5%-/spl Delta/ silica-based waveguides and reduced the single-mode fiber coupling loss to less than 0.5 dB/point. The SSC provides a large cut-position tolerance that enables angle polishing of the PLC endfaces to prevent reflection and low-loss connection of pigtail fibers. The center channel insertion loss of the AWG module was reduced from 4.2 to 2.2 dB, and the reflection was less than -60 dB.