电光聚合物波导中的锥形结构

提出并设计了一种基于电光聚合物的锥形波导,可用于单模光纤与电光聚合物波导器件之间的连接.锥形波导中采用了宽度锥形和折射率锥形结构.宽度锥形采用劈形形状,通过宽度和折射率的缓慢变化实现模场转换.劈形形状的宽度锥形具有较小的损耗且易于制作,折射率锥形可采用灰度掩膜光刻技术制作.研究了锥形波导的传输损耗与锥形波导的长度、波导宽度和厚度、材料吸收损耗等参数的关系及其优化,分析了锥形波导中的功率传输、模场分布与模式转换效率.结果显示锥形波导的传输损耗小于0.37 dB,光纤-波导-光纤的连接损耗优于1.62 dB,对插入损耗的改善达到8.78 dB,模场转换效率达到了83.7%.     

Optical Fiber Index Taper–Theoretical Analysis and Experiment Demonstration

We discuss theoretical analysis of optical fiber taper with its refractive index gradually changing alone its propagation axis caused by photosensitivity. The numeric results for two different taper shapes in step-index fiber show that the couplings of fundamental mode to the reflected mode and to high-order modes is relatively small provided the change is gradual. The fundamental mode has the capability of excellent transmission that can adjust itself adiabatically to the refractive index change. The experiment demonstrates its effectiveness for optical interconnection with different mode-fields     

纤维光锥有效透过率的理论分析

光锥的有效透过率不仅影响光锥与CCD的耦合效率,而且会影响到耦合器件的信噪比.本文主要从理论上讨论了影响光锥有效透过率性能的因素,从纤维光学元件的实际内部结构推导出了其实际有效填充率,从光线在光锥中的传输特征推导出了光线在光锥中传播时产生的衰减损耗,最后提出了提高光锥有效透过率的方法和途径.     

扫描近场光学显微镜光纤锥中导波反射特性

利用局部模耦合模型理论上分析了扫描近场光学显微镜光纤的光场性质,给出光纤维中存在的正,反向传播的基模场微分方程,以及基模反向耦合系数的数值计算结果,其最高反射系数达１％左右。这种反射光可起着光纤维激光器谐振腔输出端镜的作用。     

光锥与CCD耦合效率的理论分析

光锥与CCD的耦合技术是研制ICCD图像传感器的关键技术,本文主要从理论上分析并讨论了光锥与CCD耦合器件的耦合效率及其影响因素,进一步分析讨论了耦合效率对耦合器件信噪比的影响.证明了光锥与CCD的耦合效率不仅降低ICCD探测效率而且降低ICCD信噪比,并提出了提高光锥与CCD耦合效率的方法和途径.     

The measurement of sucrose concentration by two-tapered all-fiber Mach–Zehnder interferometer employing different coupling structures and manufacture processes

The sucrose concentration measurement and characteristics of light coupling taper structure on sensitivity with various fabrication processes of taper structure for all-fiber Mach–Zehnder interferometer (AFMZI) are presented. Using fusion splicer with electrical discharge, the standard single-mode fiber is employed to be fabricated as conical coupling/decoupling taper structure. The basic two fabrication processes are designed as single fusion-stretching (SFS), multiple fusions without stretching (MF). The third advanced process is composed of SFS and multiple fusions without stretching processes, and called multiple fusions with single stretching (MFSS). Various types of coupling/decoupling taper structures were fabricated based on the three kinds of fabrication processes. The effects of geometry shape including taper waist, taper angle, and sensing length on sensing sensitivity of AFMZIs are estimated. The modifications of fiber core and cladding induced by thermal effect affect the refractive index distributions and shapes of taper structure. The effects of refractive index changes of fiber core and cladding on sensing sensitivity are also discussed. The AFMZI was tested by measuring aqueous sucrose solution of refractive index unit (RIU) from 1.333 to 1.420 RIU. The optical spectrums are measured by a spectrometer. The spectrum dip shifts and sensing sensitivity was measured and calculated, respectively. As shown in results, sensing sensitivities of AFMZIs of taper structure fabricated by MFSS and multiple fusions without stretching processing are generally higher than SFS. The reasons could be aimed on materials modification through thermal effect on blurring fiber core-cladding interface and proper taper angle of taper structure. The more homogeneous refractive index distribution on fiber core-cladding interface, the more detecting light power decoupled through core-cladding interface to interact with exterior environment and enhance the sensing sensitivity. Similarly, an appropriate taper angle also provides a better coupling/decoupling performance. The optimal sensitivities relative to low refractive index, high refractive index, and full refractive index range are 87.62, 133.55, and 104.20 nm/RIU, respectively, and the corresponding sensing length are 30, 50, and 30 mm, respectively, with taper angle of 25° and taper waist of 40 μm.     

Efficient input and output fiber coupling to a photonic crystal waveguide

The efficiency of evanescent coupling between a silica optical fiber taper and a silicon photonic crystal waveguide is studied. A high-reflectivity mirror on the end of the photonic crystal waveguide is used to recollect, in the backward-propagating fiber mode, the optical power that is initially coupled into the photonic crystal waveguide. An outcoupled power in the backward-propagating fiber mode of 88% of the input power is measured, corresponding to a lower bound on the coupler efficiency of 94%.     

塑料光纤双锥与半球腔的活动耦合效应

报道了用氮氖激光实现的塑料光纤双锥与介质半球(称半球腔)之间的活动耦合效应。测量了光纤双锥的发射效率，并测量了锥腔耦合效率与半球腔的表面积、锥腔距离之间的关系。根据这种效应，可以制成塑料光纤活动耦合器；如果再加上调谐滤波器，可制成适合塑料光纤通信网用的信号上下载装置。     

Modal coupling in fiber tapers decorated with metallic surface gratings

An interference-based scheme for fabricating periodic metal gratings on one side of the uniform waist of optical fiber tapers has been developed. Optical characterization of a 5 mm long, 511 nm period gold grating fiber taper with a 10 microm diameter reveals backward coupling to both guided and radiation modes that is explained by using an analytical mode-coupling analysis. A refractometer based on this grating taper has a high and constant sensitivity over a large refractive index operating range of 1 to 1.41.     

大容差光纤耦合技术研究

设计了一种新型的耦合系统,该耦合系统由大口径聚焦透镜、1/4节距自聚焦透镜、锥形光纤和球端光纤四部分组成.分析了自聚焦透镜压缩发散角和球端光纤增大数值孔径的机理,给出了计算锥形光纤参量的详细流程.采用大口径透镜和1/4节距自聚焦透镜有效增大径向位置容差和角度容差,然后通过锥形光纤压缩光束半径将激光耦合进球端光纤.仿真实验结果表明,该系统耦合在r<3 mm,－1<θ<1.5范围内的耦合效率稳定保持在50%以上.     

光纤纤芯及包层模有效折射率计算及仿真

光纤结构设计、模间色散求解、光纤光栅模式耦合等问题的研究, 都需要对光纤纤芯及包层模的有效折射率进行精确计算. 本文以光纤三层结构模型为基础, 结合该模型下的模式本征方程, 使用截弦法求解了纤芯模有效折射率, 并将计算结果与COMSOL软件模拟的对应纤芯模的传输光场进行对比, 验证了计算结果正确.使用区间遍历算法对包层模有效折射率进行了求解, 与已有的传统方法相比, 该方法可以有效防止求解过程中根的遗漏、避免特征方程产生的奇点, 并能保证模式的正规性.本文采用Mathematica软件对求解过程进行仿真, 获得了纤芯模和包层模有效折射率与波长关系曲线. 关键词： 光纤传输模式 有效折射率 截弦法 区间遍历算法     

相位匹配下锥形光纤激发出的回廊模谐振

分别计算不同直径下锥形光纤基模和玻璃微球谐振腔内最低阶径向回廊模的传播常量,利用相位匹配条件,作出了锥形光纤与石英玻璃微球腔的直径对应关系曲线.在此基础上,选择锥腰直径2.8 μm左右的低损耗锥形光纤与直径143.1 μm球形度很好的玻璃微球腔进行近场耦合以激发球内的最低阶径向回廊模谐振,在锥形光纤的两端进行通光测试,在输出端获得了等间距分布的窄线宽滤波谱线,其吸收峰位置与利用Mie理论计算的球内最低阶径向回廊模谐振峰位置相一致.     

2×2熔锥型单模光纤耦合器的模型

选择适当的连续函数描述了熔锥型耦合器熔锥形状的渐变特性及其相互位置关系,然后分别应用局部模式理论和变分法分析了横截面沿纵向变化的锥形区域和横截面近似不变的耦合区域内的耦合行为,得出了耦合器中任一横截面处的耦合系数和耦合功率表达式计算表明,熔锥型耦合器的总功率耦合主要发生在耦合区域,在两锥形区域,对于纤芯归一化频率小于1.08的部分,也发生了相当程度的耦合为了使耦合器的理论模型更接近于实际物理情况,锥形区域的耦合作用也是不容忽略的,从而得到了一个更精细的熔锥型光纤耦合器的模型.     

Optical microresonator based on hollow sphere with porous wall for chemical sensing

A porous-wall hollow glass microsphere (PW-HGM) was investigated as an optical resonator for chemical vapor sensing. A single mode optical fiber taper was used to interrogate the microresonator. Adsorption of chemical molecules into the nanosized pores induced a refractive index change of the thin wall and thus a shift in its resonance spectrum. The PW-HGM resonator had shown higher vapor detection sensitivity in comparison with a solid microsphere under similar test conditions.     

基于非球面透镜的空间光场光纤耦合系统研究

针对全光纤激光雷达中空间光场与单模光纤的耦合问题,设计了基于非球面透镜的望远镜光纤耦合系统.利用ZEMAX软件以单模光纤耦合效率为优化目标对其结构参量进行优化设计,然后分别用LED和激光器作为光源进行初步实验,比较直接耦合和非球面透镜耦合效果.实验结果表明,采用非球面透镜耦合可使多模光源的耦合效率比直接耦合增加约47％,与仿真结果45％非常接近,且不同芯径耦合光功率之比大略等于芯径比平方;而该耦合方式可使单模光源的耦合效率增加约20％,且耦合进不同小芯径光纤的耦合效率之比约为其芯径比平方的2.4倍,这对构建全光纤转动喇曼激光雷达系统具有重要意义.     

激光熔融拉锥型微型光纤耦合器设计

采用聚焦红外激光光束进行熔融加热,针对激光熔融拉锥型光纤耦合器设计了一种熔融区域长度为200 μm的微型光纤耦合器.使用光束传输法对拉锥长度和耦合区域的宽度进行了模拟并与实验结果比较,在1320 μm的拉锥长度和14 μm的耦合宽度处找到了最优化且低损耗的耦合器尺寸配置.     

Compact optical fiber curvature sensor based on concatenating two tapers

A low-loss, compact, and highly sensitive optical fiber curvature sensor is presented. The device consists of two identical low-loss fused fiber tapers in tandem separated by a distance L. When the optical fiber is kept straight and fixed, no interference pattern appears in the transmitted spectrum. However, when the device is bent, the symmetry of the straight taper is lost and the first taper couples light into the cladding modes. In the second taper, a fraction of the total light guided by the cladding modes will be coupled back to the fundamental mode, producing an interference pattern in the transmitted spectrum. As the fiber device is bent, visibility of the interference fringes grows, reaching values close to 1. The dynamic range of the device can be tailored by the proper selection of taper diameter and separation between tapers. The effects of temperature and refractive index of the external medium on the response of the curvature sensor is also discussed.     

基于少模光纤被动调Q柱矢量光光纤激光器

通过单模光纤和少模光纤熔融拉锥耦合的方法制备出模式转换器,而后将一层多壁的碳纳米管薄膜作为可饱和吸收体覆盖到拉锥光纤的锥区,形成一种可饱和吸收体柱矢量光器件.结合调Q光纤激光器和模式转换器件的优势,可以简单高效地产生脉冲柱矢量光束,并得到具有峰值功率高、模式纯度高等特点的脉冲高阶模式激光输出.通过实验实现了中心波长为1560nm、最大单脉冲能量和最大峰值功率分别为116nJ和57mW的稳定调Q脉冲输出.通过调节光路中的偏振控制器,可以分别实现径向和角向偏振的调Q脉冲激光的输出.     

A rigorous analysis of the distribution of power in plastic clad linear tapered fibers

An analytical investigation is presented of the propagation of power in a step-index plastic clad tapered optical fiber operating in the infrared region of the electromagnetic (EM) spectrum. The chosen materials are widely used in low cost optical links. It is assumed that the taper section has a linear profile. Following rigorous analytical approach, the general expressions for power in the core and the cladding sections are derived, and a study is presented of the variation of the relative power along the propagation direction in respect of different (meriodinal and skew) lower order modes. It is observed that, in general, the confinement of power is fairly high in the core section, and the confinement increases with the increase in the taper length and/or mode index. In the cladding region, the confinement decreases for higher taper lengths.     

Nanotaper for compact mode conversion

We propose and demonstrate an efficient coupler for compact mode conversion between a fiber and a submicrometer waveguide. The coupler is composed of high-index-contrast materials and is based on a short taper with a nanometer-sized tip. We show that the micrometer-long silicon-on-insulator-based nanotaper coupler is able to efficiently convert both the mode field profile and the effective index, with a total length as short as 40 microm. We measure an enhancement of the coupling efficiency between an optical fiber and a waveguide by 1 order of magnitude due to the coupler.