高斯光束到光纤的单透镜耦合

分析了基模高斯激光束到单模和多模光纤的单透镜耦合过程中的各种损耗,把多模光纤的光场用高斯分布近似,采用模场耦合理论计算了基模高斯光束到单模和多模光纤的单透镜耦合效率.模拟计算了当激光-光纤耦合系统的工程参数(光束束宽、光纤数值孔径和光纤的纤芯芯径)一定时,单透镜耦合效率与所选用透镜的焦距之间的关系.并利用532mn激光(M2≤1.05)在几种不同焦距的透镜下对纤芯直径为3.μm的单模光纤和25μm的多模光纤进行了耦合效率的测定实验,得到了与理论计算基本吻合的实验结果.     

低损耗离子交换玻璃基光波导制备与分析

考虑到离子交换和离子扩散工艺的特殊要求, 设计并熔制了适合于离子交换工艺的硅酸盐玻璃材料SiO₂-B₂O₃-Al₂O₃-R’O-R₂O（R’=Ca, Mg; R=Na, K）. 采用Ag⁺/Na⁺熔盐离子交换和电场辅助离子扩散工艺在这种玻璃材料基片上获得了掩埋式条形光波导. 光学显微镜和电子探针分析表明高折射率的Ag⁺扩散区位于玻璃基片表面以下约10μm处, 形成光波导的芯部. 光波导芯部尺寸约为8μm×8μm, 与单模光纤芯径尺寸相当, 保证了较低的光纤耦合损耗. 对光波导的测量结果得出：在波长为1.5μm处条形光波导的传输损耗约为0.1dB/cm, 与单模光纤的耦合损耗约为0.2~0.3dB. 条形光波导的传输损耗与材料本身的损耗接近, 表现出掩埋式光波导的低损耗特征. 分析表明, 经过进一步优化, 这种光波导制备技术可用于低损耗光波导器件的制作.     

阵列波导光栅解复用器光谱响应特性分析

基于单模光波导本征模场及其端面衍射场分布的高斯近似表达,推导出两个端面非接触光波导耦合的耦合系数的函数表达式,并基于此推导出阵列波导光栅解复用器的简单光谱响应效率的函数表达式。建立了分析阵列波导光栅解复用器光谱响应特性的简洁数学模型,阐明了阵列波导光栅解复用器对通道中心频率的响应度和相邻信号通道间的串扰与基本参数的关系,为设计和分析阵列波导光栅解复用器提供了理论基础。     

基于SOI光波导的损耗测试与优化

利用电子束光刻技术,制备了带有氧化硅包层的SOI光波导结构,对其传输模态及损耗进行了详细的理论分析,并分别对波导的传输损耗和耦合损耗进行了测试.测试结果验证了单模传输模态时的传输损耗较低,在波导层上添加覆盖层可以将波导传输损耗降低至3.96dB/cm,利用光栅垂直耦合可以大大降低光纤-波导的耦合损耗,耦合效率可以达到32.7%.     

湍流下自由空间光通信的光纤耦合效率及补偿

采用光纤部件的自由空间光通信系统需要把接收到的光束耦合进单模光纤中,然而由于大气湍流的影响,使光纤耦合效率下降.本文把基于大气湍流参数的单模光纤耦合效率表达式推广到斜程传输情景,仿真了耦合效率与湍流强度及传输距离和天顶角之间的关系.为了补偿湍流效应,提高光纤耦合效率,本文提出了用一种新颖的无模型盲优化波前校正技术,用随...     

用于Triplexer Monitor的波长不敏感耦合器

为了提高Triplexer Monitor的光信号采样性能和集成度,提出一种基于非对称锥形波导结构的波长不敏感耦合器.该耦合器采用SiO2-on-Si掩埋型光波导结构,位于中心部位的锥形波导构成耦合区,与之衔接的S型弯曲波导实现信号光的输入和输出.采用传输矩阵法分析了光监测端口输出的归一化的耦合光功率,分析时将耦合区的中心部位作为非对称矩形波导而外侧作为对称矩形波导.利用光束有限差分传播法(FDBPM)和MATLAB数值仿真得出:当耦合区中心非对称矩形波导宽度分别为5.50μrn和3.35 μm时,对于1 300 nm到1 600 nm的输入光波长范围,可实现光监测端口4％～8％的归一化耦合光功率.特别的,在1310nm、1490 nm和1550 nm输入光波条件下,耦合器在输出端的分光比分别为:92∶8、96∶4和93∶7,同时TE模和TM模的分光比变化保持在5％以内.所设计的波长不敏感耦合器具有体积小、可靠性高等优点,适合与PLC型的Triplexer实现单片集成.     

LDA光纤耦合高效率高亮度激光输出研究

为了获得LDA(激光二级管阵列)光纤耦合高效率高亮度激光输出,光纤的芯径要尽可能小,并且耦合光束的光参数积必须小于耦合光纤的光参数积,因此必须对耦合光束进行整形。通过比较,选用反射整形法将慢轴的光参数积压缩到了原来的1/4。将LDA光束与芯径400靘,数值孔径0.37的光纤进行耦合试验,得到的耦合效率约为48%,亮度达到108量级。     

玻璃基掩埋式光波导堆栈的制作与表征

在硅酸盐光学玻璃基片上制作了光波导堆栈, 这种光波导堆栈通过Ag⁺/Na⁺熔盐离子交换和电场辅助离子扩散技术顺次制作了两层掩埋式光波导. 对光波导堆栈的横截面显微结构进行了观察, 并对堆栈中两层波导的损耗特性进行了测试. 所获得的光波导堆栈中的上、下两层波导芯部分别位于玻璃表面以下14和35 μm处; 上层光波导芯部尺寸约为12 μm×7 μm; 下层光波导芯部尺寸约为9 μm×8 μm. 通光测试显示两层波导在1.55 μm工作波长下均为单模光波导, 且两者之间没有相互耦合. 损耗测试分析结果显示: 堆栈中两层光波导的传输损耗均约为0.12 dB/cm,与单模光纤之间的耦合损耗分别为0.78和0.73 dB. 分析表明, 这种光波导堆栈在玻璃基集成光芯片的高密度集成方面具有很好的应用前景.     

基于光折变光栅的可调谐滤波方案及特性分析

在LiNbO3单模波导上利用双光束干涉可形成光折变波导光栅,针对粗波分复用系统提出了通过实时改变双光束之间的夹角进而改变光栅间距,实现可调谐滤波的方案.利用光折变动力学理论,得到光栅调谐时间在毫秒数量级.研究发现,适当提高光强和增加杂质掺杂浓度可提高衍射效率、减少光栅初次建立时间.基于耦合波理论的数值模拟结果表明,增大光栅长度能使衍射效率提高且带宽变小,而增加折射率调制度使衍射效率提高但同时带宽变宽.在折射率调制度为8×10-5,光栅长度大于12mm时,可获得91％以上的衍射效率和小于0.08 nm的带宽.     

一种单模光纤双高斯耦合透镜的设计与优化

针对目前单模光纤耦合使用球面透镜存在较大像差、影响耦合效率的问题,提出了一种利用双高斯透镜作为耦合透镜消除像差、提高耦合效率的方法。双高斯透镜的特殊结构可以使得在使用球面镜时很好地消除包括球差在内的大部分像差。利用ZEMAX光学设计与仿真软件设计优化了一种用于780 nm波长、5μm模场直径单模光纤的双高斯耦合透镜,经过计算,其成像质量的评价函数达到10~(-5)量级,耦合效率达到82.07%。为单模光纤耦合透镜的设计和使用提供了一种新的思路。     

Coupled-wave Analysis of the Bragg Effect Waveguide Coupler

Abstract

A coupled-wave analysis is presented for the Bragg effect waveguide coupler. This device consists of a slanted volume phase grating which is integrated inside the lightguiding layer of an optical waveguide. The wave propagation is described by a set of leaky wave modes. Self-consistency relations are derived to determine the angular mode spectrum and the corresponding radiation loss coefficients. A maximum input coupling efficiency of 80% is predicted for an incident Gaussian beam. The power of a waveguide mode should be emitted into a single output beam reaching an efficiency of almost 100%.     

Optimized coupling of a Gaussian beam into an optical waveguide with a grating coupler: comparison of experimental and theoretical results

The coupling efficiency of grating couplers is derived for a Gaussian incident beam. Its optimum value depends on the beam waist and on the position of a light spot with respect to the coupler edge for given grating parameters. The characteristic coupling length has been experimentally determined for the grating coupler studied. Relative measurements of the coupling efficiency as a function of incident beam characteristics are in good agreement with the numerical results.     

Laser direct writing polymeric single-mode waveguide devices with a rib structure

A focused argon-ion laser beam is used on a spin-coated polymeric thin-film deposited upon a SiO2/Si substrate to polymerize the core for fabrication of Gaussian profile optical channel waveguides. A rib structure that allows only the fundamental mode to propagate even with its higher dimension and high-index contrast between the core and the cladding was fabricated. When the thickness of the core-index region outside the rib section decreases, the waveguide produces higher-order modes at the output. The waveguide reported here has cross-sectional dimensions and numerical apertures that match the single-mode fibers for efficient coupling. I used a mixture of two intermiscible acrylate monomers for the cladding and the core of the waveguides. The polymerization process and its dependent dwell time or scan speed and the laser power intensity are shown. I present the operational characteristics of directional couplers using a rib waveguide structure with a core-cladding index difference.     

Foundations for low-loss fiber gradient-index lens pair coupling with the self-imaging mechanism

A fiber-optic collimator that emits a Gaussian beam with its beam waist at a certain distance after the exit face of the lens is labeled a self-imaging collimator. For such a collimator, the waist of the emitted Gaussian beam and its location are partly dependent on the properties of the gradient-index (GRIN) lens. Parameters for the self-imaging collimator are formulated in terms of the parameters of a GRIN lens (e.g., pitch, core refractive index, gradient index, length) and the optical wavelength. Next, by use of the Gaussian beam approximation, a general expression for the coupling power loss between two self-imaging-type single-mode fiber (SMF) collimators is, for the first time to our knowledge, derived as a function of three types of misalignment, namely, separation, lateral offset, and angular tilt misalignment. A coupling experiment between two self-imaging collimators with changing separation distance is successfully performed and matches the proposed self-imaging mechanism coupling loss theory. In addition, using a prism, lateral offset, as well as angular tilt, misalignments are experimentally simulated for a two self-imaging collimator coupling condition by a single collimator reflective test geometry. Experimental results agree well with the proposed loss formulas for self-imaging GRIN lenses. Hence, for the first time to our knowledge, the mathematical foundations are laid for employing self-imaging-type fiber collimators in SMF-based free-space systems allowing optimal design for ultra-low-loss coupling.     

Coherent beam combination of fiber lasers with a strongly confined waveguide: numerical model

Self-imaging properties of fiber lasers in a strongly confined waveguide (SCW) and their application in coherent beam combination (CBC) are studied theoretically. Analytical formulas are derived for the positions, amplitudes, and phases of the N images at the end of an SCW, which is important for quantitative analysis of waveguide CBC. The formulas are verified with experimental results and numerical simulation of a finite difference beam propagation method (BPM). The error of our analytical formulas is less than 6%, which can be reduced to less than 1.5% with Goos-Hahnchen penetration depth considered. Based on the theoretical model and BPM, we studied the combination of two laser beams based on an SCW. The effects of the waveguide refractive index and Gaussian beam waist are studied. We also simulated the CBC of nine and 16 fiber lasers, and a single beam without side lobes was achieved.     

Dual-fiber collimator with elliptical spot for optical MEMS devices

Fiber collimators are widely used in optical communication components and fiber-optic sensors. Ordinary fiber collimators are made with a circular beam waist radius from 100?μm to 300?μm. The circular beam waist is too large to switch or shut the beam for certain micro-electro-mechanical system (MEMS) actuators (such as MEMS linear mirrors). In this paper, a dual-fiber collimator with an elliptical spot is proposed to meet the demands of MEMS optical devices. The elliptical spot collimator has been designed and fabricated, the beam waist spot of which is an elliptical spot with a 231.6?μm long-axis radius and a 12.87?μm short-axis radius, and its coupling loss is 0.37?dB.     

Coupling characteristics of cladding modes in tilted optical fiber bragg gratings

We have studied both theoretically and experimentally the effect of grating tilting on the coupling between the fundamental core mode and the cladding modes in an optical fiber Bragg grating. The coupling is shown to be very sensitive on the tilting angle. It is also shown that tilting angle has to be minimized in fibers with designs to suppress the coupling between the fundamental core mode and the cladding modes. We have also studied the single, strong loss peak accompanying the Bragg reflection peak in depressed-cladding fibers, thus showing a good agreement between behavior that is measured and that is predicted theoretically.     

亚波长波导光栅导模共振研究

弱调制介质光栅可等效为平板波导,经其衍射的高级次子波与波导模式耦合时,形成导模 共振。由高级子波在介质光栅中的光程及菲涅耳相移,导出了垂直入射时弱调制介质光栅共振位置的解析表达式,其预测结果和严格耦合波理论所得值一致。导模共振对入射波参数和光栅参数极为敏感,具有窄带效应,可用来制作窄带滤波片。     

Effective way of reducing coupling loss between rectangular microwaveguide and fiber

We introduce an anamorphic photonic crystal fiber (PCF) produced by postprocessing techniques to improve the coupling loss between a conventional single-mode fiber and rectangular microwaveguide. One end of the round core is connected with the conventional fiber, and the other end of the rectangular core is connected with the rectangular microwaveguide, then the PCF is tapered pro rata. In this way, the loss of mode mismatch between the output of the conventional fiber and the input of the waveguide would be reduced, which results in enhanced coupling efficiency. The conclusion was confirmed by numerical simulation: the new method is better than straight coupling between the optical fiber and the rectangular microwaveguide, and more than 2.8 dB improvement of coupling efficiency is achieved.