波导厚度变动、偏振变动以及折射率变动脱敏高分子宽带耦合器设计

针对高分子光波导在制造工艺中波导芯厚度难以控制、芯层和包层的折射率差变动时的随机性以及材料各向异性引起的偏振态依赖性等实际问题,提出了采用抗波导芯厚度误差、抗折射率差变动和抗偏振变动的宽带波导耦合器回路结构的解决方案,给出了设计的理论和方法。在实测数据的基础上,进行了带宽为120nm的3dB氟化聚酰亚胺波导耦合器设计。由该器件的三维BPM仿真结果表明,在上述带宽上,波导芯厚度的变动范围为7～8μm、相对折射率差变动范围为0 24%～0.30%,两个正交偏振态都具有(50±2.0)%功率输出比的良好特性。     

Design and analysis of a vertical directional coupler between a three-dimensional plasmonic slot waveguide and a silicon waveguide

The design of a vertical directional coupler between a three-dimensional plasmonic slot waveguide and a silicon waveguide is theoretically investigated in detail. It consists of two steps: the design of isolated plasmonic slot waveguide and silicon waveguide and the determination of the gap between the two waveguides and the length of a coupling region. The designed structure transfers 70.8% of the power carried by the silicon waveguide mode to the plasmonic slot waveguide mode when the gap is 150 nm and the coupling length is 2.14 μm. The wavelength dependence of our vertical directional coupler is also studied. The analysis shows that the amount of the transferred power changes slightly over a very wide wavelength range between 1.40 μm and 1.61 μm. Moreover, if we employ the fabrication technology for silicon photonics, it is quite tolerant to the variation of the length of its coupling section. Finally, the vertical directional coupler is considered for a polarizer.     

定向耦合器光波导开关阵列研究

在Z-LiN_bO₃衬底上制做了Ti扩散定向耦合电光开关阵列。把光纤固定在我们自己设计的衬底上,就做成了2×2开关。 本文讨论了三种光电开关。着重论述了Ti扩散定向耦合器的原理和交替Δβ法。在1.3μm的光波下改善了器件特性。     

跑道型结构光子晶体波导定向耦合器

鉴于波导定向耦合器在集成光路以及光电集成方面的广泛应用,提出了一种基于光子晶体波导间高效耦合的光子晶体定向耦合器。通过主波导和耦合波导间的耦合,可以实现对波长为1 490 nm和1 550 nm电磁波的高效分光。在将器件长度控制在30 μm左右的同时,其总效率高达93.05%。另外,发现主波导和耦合波导间介质柱结构参数对电磁波的耦合周期有着极大的影响。并通过将介质柱沿z方向拉伸0.1a(a为晶格周期),设计了工作波长为1 530 nm和1 540 nm的光子晶体定向耦合器,器件长度仅为60 μm。通过拉伸介质柱的纵向长度,可以大幅减小耦合周期,这对缩小器件体积以及实现更为密集的波分复用有着重要的意义。     

Vertical coupling characteristics between hybrid plasmonic slot waveguide and Si waveguide

For development of complementary metal–oxide–semiconductor (CMOS)-compatible integrated optical circuits, vertical directional coupling between a hybrid plasmonic slot waveguide and a Si waveguide is theoretically investigated in detail. To determine the vertical separation gap and efficient coupling length, we investigate the characteristics of the even and odd supermodes at a wavelength of 1.55 μm. The vertical coupler transfers 90% of the power carried by the Si waveguide to the hybrid plasmonic slot waveguide after normalizing to reference waveguides when the gap is 60 nm and the coupling length is 2.6 μm. Because of the lossy hybrid guided mode in the plasmonic waveguide, the transmitted power exhibits damped sinusoidal behavior depending on the overlapping length. The proposed vertical coupler shows more efficient light coupling between a dielectric and plasmonic waveguide in comparison to the other types of hybrid coupler, and can be exploited further for on-chip integrated opto-electronic circuits.     

Optical Coherence Tomography Implemented by Photonic Crystal Fiber

We report a photonic crystal fiber (PCF)-based optical coherence tomography (OCT) system, in which conventional single-mode fiber for the transmission line and the fiber coupler for the beam splitter/combiner are replaced with PCF and PCF coupler. The PCF coupler fabricated using the fused biconical tapered (FBT) method showed a nearly flat coupling ratio over a broad spectral bandwidth of 400 nm, which provided an axial resolution of 3-μm for OCT imaging. With a white-light source, the 8-μm thick air gap between two stacked cover glasses was measured, and with a conventional superluminecent diode (SLD) source, the in vitro images of rat eye and Misgurnus mizolepis skin were successfully obtained. The PCF and PCF coupler might enable a white-light as the source for the cost effective and high-resolution OCT system.     

Gain-induced soliton switching in fiber nonlinear directional coupler

With study for switching characteristics and output coupling ratio of fiber nonlinear directional couplers (NLDC), we found that the influence elements on the switching characteristics and output coupling ratio had gain of core 1 and 2, nonlinear coefficient of those, the input power and width of input soliton. We also found numerically that switching efficiencies were improved by controlling gain of core 1, different output coupling ratio would be obtained by controlling gain of core 1 or 2. And we can change the gain by changing pump power of the optical fiber amplifiers. From this, we also made fiber coupler which output coupling ratio was changeable.     

一种硅基SiO2波导耦合器的设计与分析

波导耦合器是组成光纤传感系统和光纤通信系统光收发组件及模块的重要元器件,是实现光收发模块一体化光电集成的基础。给出了一种用光纤陀螺系统的X型四端口波导耦合器的工作原理,采用有效折射率法和BPM(Beam propagation method)法建立了耦合器的数学模型,计算并分析了耦合器尺寸在尽可能小的情况下和在满足单模传输的条件下耦合器的耦合系数、有效耦合长度、分光比以及回波损耗等参数之间的关系,并对其关键技术进行了系统的研究。仿真结果表明,所设计的波导耦合器在低损耗情况下分光比可达到50%∶50%,耦合器全长为33.5mm,输入输出波导间距为410μm,芯层截面积为6μm×6μm。     

A very short vertical directional coupler with polarization-insensitive high extinction ratios

We propose a very short vertical directional coupler with polarization-insensitive high extinction ratios. The structure of the coupler has two deep-ridge waveguide structures in the upper and lower parts which can be implemented using a double-sided wafer process. The coupling length and extinction ratios of the vertical directional coupler with symmetric structures decrease as the thicknesses of the inner cladding layer and core layer decrease. The extinction ratio is improved using a slight asymmetry in the refractive indices of two core layers. As the thicknesses of the inner cladding layer and core layer decrease, the length of the vertical directional coupler for extinction ratios greater than 30 dB of both TE and TM modes decreases. A vertical directional coupler with a very short length less than 100 μm and polarization-insensitive high extinction ratios greater than 30 dB can be implemented using the structure proposed in this paper.     

Polariton propagation in coupled quantum wire waveguides

The propagation of the excitonic polariton along the directional coupler consisting of adjacent parallel GaAs quantum-wire waveguides is simulated by using a finite element method. It is found that the coupling length is as short as 2.5-4 μm, which is three orders of magnitude shorter than the conventional optical directional coupler made of bulk GaAs. Such short coupling length will make it possible to fabricate extremely small optoelectronic devices such as directional-coupler-type switches.     

采用光纤消光法检测脉冲激光测距仪消光比的研究

阐述了光纤消光法检测脉冲激光测距仪消光比的测试原理,采用光纤消光法分析了光纤对大功率脉冲激光的耦合与传输等关键技术问题,提出了0．22NA、400μm大功率传能光纤方案,并设计了耦合器和光学系统,分析了聚焦透镜的损耗、光纤端面的损耗、光纤耦合器与光纤的对准误差等影响耦合效率的因素,计算了光学系统弥散斑数据,接收光学系统和发射光学系统在1ω视场的弥散斑分别为9．03μm和10．6μm。设计分析结果对光纤消光法的工程应用具有一定的研究价值。     

双芯光子晶体光纤宽带定向耦合器研究

利用半矢量有限差分法设计了具有低折射率双芯的光子晶体光纤宽带定向耦合器,并数值计算了双芯光子晶体光纤的结构参量对耦合性能的影响.数值结果表明,通过优化选取光子晶体光纤包层结构参量和纤芯掺杂浓度,双芯光子晶体光纤耦合器可以实现宽带耦合.在1.22~1.65 μm 波长范围内其耦合长度稳定在26637 nm±235 nm范围内,耦合器设计成耦合比为50%和10%,分别实现了耦合比为（50±0.702）%和（10±0.664）%的良好特性.     

Transverse light guides in microstructured optical fibers

A novel class of microstructured optical fiber coupler is introduced that operates by resonant, rather than proximity, energy transfer by means of transverse light guides built into a fiber cross section. Such a design permits significant spatial separation between interacting fibers, which, in turn, eliminates intercore cross talk owing to proximity coupling. A controllable energy transfer between the cores is then achieved by localized and highly directional transmission through a transverse light guide. The main advantage of this coupling scheme is its inherent scalability, as one can integrate additional fiber cores into the existing fiber cross section simply by placing the cores far enough from the existing optical circuitry to prevent proximity cross talk and then making the necessary intercore connections with transverse light wires, in direct analogy with on-chip electronics integration.     

Spectral excess attenuation of monomode optical fibers with sinusoidally perturbed core radius

The spectral excess attenuation caused by coupling between the guided HE₁₁ mode and radiation modes is calculated with the aid of the formula derived by Marcuse for the radiation loss of a monomode optical fiber with step-index profile and sinusoidally perturbed core radius. The pronounced minima and maxima of the spectral excess attenuation curve converge as the spatial frequency of the perturbation of the core radius increases. Even perturbation amplitudes as small as 0.01 μm may lead to excess attenuations of the order of 10 dB/km if the radiation wavelength does not coincide with an attenuation minimum. The spectral behavior of the excess attenuation can be utilized to design fibers which act as optical filters.     

High efficiency fiber coupling to silicon sandwiched slot waveguides

The design of a fiber coupler for high efficiency light coupling to silicon sandwiched slot waveguides is reported. The proposed fiber coupler is based on the inverted taper approach. Parameters have been optimized to maximize coupling efficiency for λ = 1550 nm and TM polarization. Maximum coupling efficiencies of 93% for a inverted taper length of 150 μm and a inverted taper tip width of 40 nm have been obtained by means of the overlap integral and 3D beam propagation method (BPM) simulations.     

Coupling and crosstalk characteristics of hybrid silicon plasmonic waveguides

In this paper, the design and analysis of an ultracompact coupler based on a hybrid silicon plasmonic waveguide (HSPW) is proposed and its coupling and crosstalk characteristics have been theoretically investigated for the development of optical interconnects that can be realized using well-established complementary metal-oxide-semiconductor-compatible fabrication techniques. To determine the minimum horizontal separation distance and efficient coupling length for the designed coupler, the symmetric and antisymmetric supermodes are obtained and their characteristics are studied at a wavelength of 1.55 μm. Efficient light coupling is exhibited by the HSPW coupler with 75 % of power transfer between the two HSPWs with ultrashort coupling length of 2.14 μm when the separation distance is 50 nm. Further, it is shown that the crosstalk is significantly reduced with the insertion of metallic strip between the two HSPWs for realizing highly dense integrated plasmonic circuits.     

General coupled-mode analysis for gain-guided, index-antiguided fibers, and index-guided fibers

Coupling properties of two gain-guided, index-antiguided (GG + IAG) fibers, or GG + IAG fibers and index-guided (IG) fibers, were investigated by the further general coupled-mode theory. The theory can explain any situation of two fiber coupling. The interesting results were obtained by the numerical computation method. For two GG + IAG fiber coupling, total power was decreased as rising real-valued refractive-index difference (real part of refractive-index difference between core and cladding, RVRID), while the power of one GG + IAG fiber was damped oscillations with increased core separation. In the GG + IAG fiber and IG fiber coupler, the variation of the RVRID could change coupling characteristics. These results are different from two IG fibers coupling, and the general coupled-mode theory may provide meaningful references for new concepts of directional coupler and pumping technology of GG + IAG fiber.     

耦合器分光比的精确控制

利用矩形近似理论对用熔锥法制作的耦合器分光比进行了分析。结果表明,影响分光比的主要因素为耦合区长度。给出了两者间变化的理论公式,并在实验中得到了证实。CorningSMF28光纤耦合器分光比随耦合区长度变化的实验值为0 04%/μm,实验值与理论值基本一致。通过调节耦合区长度,得到了精确的50∶50分光比的光纤耦合器。     

一种覆盖全通信波段的新型宽带偏振无关双芯光纤定向耦合器的研究

提出了一种新型的双芯光子晶体光纤, 应用全矢量有限元方法分析了光纤各种结构参数对光纤宽带特性和偏振无关特性的影响. 在此基础上优化设计了一种50:50的双芯光子晶体光纤耦合器, 在1.225—1.675 μm波长范围内实现分光比小于1%、两偏振态之间的分光比差小于0.5%的优良特性. 由于引入了仅对偏振特性影响明显的相对独立的中心调制区, 不仅降低了光纤的优化设计难度, 而且实现了与普通单模光纤相匹配的模场特性, 能有效地降低耦合器的接续损耗与制作难度. 研究成果为研制接续损耗低、超宽工作带宽、偏振不敏感等特性的新型光定向耦合器提供了理论基础.     

基于组合透镜与渐变折射率光纤改进激光器耦合效率的新方法

提出一种利用组合透镜系统与渐变折射率光纤相结合改进激光 器管芯到单模尾纤耦合性能的新方法. 这种方法首先利用组合透镜系统对具有像 散的激光器输出光束进行整形, 然后采用渐变折射率光纤对整形后的光束进行聚焦处理, 并将处理后的的光束耦合进入普通单模光纤. 利用Jones矩阵理论分析表明, 采用这种方法可以得到86%的功率耦合效率, 1 dB插入损耗对应的渐变折射率光纤长度、 横向偏移和倾斜角容差分别为60 μm, 30 μm和2.4°, 且结构简单, 便于操作, 特别适合于大功率激射的激光模块到单模光纤的耦合. 对于提高激光器输出功率, 改善光束质量具有重要意义.