ZnO纳米线光学特性测试的倏逝波耦合

使用纳米氧化硅光纤探针,利用倏逝波耦合方法,将紫外到红外的激光成功地耦合进单根ZnO纳米线,耦合效率可达25%.实验观测了单根纳米线的荧光特性,发现ZnO纳米线光传输损耗很低.研究证明:采用透镜聚焦激发纳米线发光的传统耦合方法,只能使用特殊激发波长的光;而倏逝波耦合方法具有高效、适用性强的特点,在半导体纳米线和纳米带的光学特性研究中有广泛的应用前景.     

An Evanescent Coupling Approach for Optical Characterization of ZnO Nanowires

使用纳米氧化硅光纤探针,利用倏逝波耦合方法,将紫外到红外的激光成功地耦合进单根ZnO纳米线,耦合效率可达25%.实验观测了单根纳米线的荧光特性,发现ZnO纳米线光传输损耗很低.研究证明:采用透镜聚焦激发纳米线发光的传统耦合方法,只能使用特殊激发波长的光;而倏逝波耦合方法具有高效、适用性强的特点,在半导体纳米线和纳米带的光学特性研究中有广泛的应用前景.     

集成光杨氏干涉计生化传感器的设计和制备

报道一种结构新颖的集成光杨氏干涉计生化传感器。利用微光机电系统(MOEMS)加工工艺结合离子交换技术在玻璃基底上制作出成对的平行单模光波导阵列,并在每对波导中一条的中间区段淀积一层具有梯度末端的TiO2薄膜,覆膜波导用作传感,裸露波导作为参比,从而构成集成光杨氏干涉计芯片。研制结果表明,这种传感器与传统的集成光杨氏干涉计相比,不仅省去了Y型功率分配器和低折射率介质保护层,而且利用简单的狭缝探测器取代了昂贵的电荷耦合器(CCD)探测器,具有结构简单、制作容易和使用方便等优点。     

Optical Refractive-Index Sensor Based on Dual Fiber-Bragg Gratings Interposed With a Multimode-Fiber Taper

A new type of optical refractive-index (RI) sensor is proposed and experimentally demonstrated by using a structure of two single-mode fiber (SMF) Bragg gratings with a multimode fiber (MMF) taper in-between. The loss induced by a mismatch of waveguide structure between SMFs and MMFs is amplified by a tapering process, and is utilized for RI sensing through evanescent field. Experimental results show that the sensor possesses a tailorable sensitivity to the change of external RI and has a good linear response in the simultaneous measurement of external RI and temperature     

线性锥形光纤倏逝波传感器的灵敏度分析

倏逝波的透射深度、均匀感应区域的感应芯径和感应长度是线性锥形光纤倏逝波传感器灵敏度的主要影响因素。为了实现灵敏度的最优化设计,分别建立了倏逝波透射深度与锥形参数之间关系及有效吸收路径与感应芯径和感应长度之间关系的数学模型,讨论了不同锥形参数(发射角、锥度比、锥长)下倏逝波的透射深度,不同感应芯径和感应长度下倏逝波的有效吸收路径,并进行了仿真。仿真结果表明,选择锥形光纤几何体和合适的发射角,可使透射深度增大近3倍,当锥度比为0.4时,倏逝波透射深度最大;减小感应芯径,增大感应长度可提高倏逝波的有效吸收路径,增强纤芯表面的倏逝波与周围吸收介质的作用强度。研究结果可用来指导制作高灵敏度线性锥形光纤倏逝波传感器。     

Evanescent amplification in a single-mode optical fibre

By replacing a portion of the cladding of a single-mode fibre with a laser dye, amplification can be achieved by means of an evanescent field interaction. External gains as high as 22 dB have been measured by guiding both a pulsed pump and CW signal within the single-mode fibre.     

基于液体选择填充光子晶体光纤的波分解复用器研究

设计了一种基于液体选择填充三芯光子晶体光纤的1.31/1.55um波分解复用器。中间为缺失一个空气孔的普通二氧化硅纤芯,左右两纤芯填充了不同折射率的液体材料。根据光纤的消逝场耦合的模式理论,不对称相邻波导存在波长相关耦合。不同填充折射率的两纤芯与中间纤芯分别耦合,构成两个不同响应波长的光滤波器。通过选择合适光纤长度,可实现不同波长光的分离。采用全矢量有限元法分析了光纤的传输特性,讨论了填充不同折射率液体时波导间的模式耦合,得到了其匹配波长与耦合长度。基于光束传播法仿真发现,长度为4.88 mm的光纤能实现1.31/1.55 um波长光的解复用。     

Scalar-field theory and 2-D ray theory for bent single-mode weakly guiding optical fibers

A purely scalar theory is presented for bent single-mode, weakly guiding, optical fibers, leading to the well-known loss formula and also to simple analytical expressions for the radiating field and the evanescent field reflected by the caustic. It is also established that all these results can be derived from a simple two-dimensional (2-D) ray analysis of the cross-sectional field; the evanescent parts of the field are connected with real rays while the radiating part involves complex rays. Lastly, field-displacement effects are analyzed, within both the field theory and the ray analysis.     

Effectively nonreciprocal evanescent-wave optical-fibre directional coupler

An effectively nonreciprocal directional coupler has been demonstrated using evanescent coupling between a single-mode and a multimode optical fibre. At least 17 dB difference in coupling efficiency between transmit and receive branches has been measured. The near-field mode patterns show coupling between the single-mode fibre and a few high-order modes of the multimode fibre.     

光纤消逝场传感器传感结构的分析与应用

对光纤消逝场理论进行了详细分析,阐述了影响光纤消逝场传感器灵敏度的一些关键因素,并对几种常见的光纤消逝场传感光纤的优缺点进行了比较,主要包括圆柱形、D形、U形、锥形以及光子晶体光纤等结构的传感光纤。通过分析各种传感结构的光纤消逝场传感器的应用实例,归纳总结了提高光纤消逝场传感器传感灵敏度的一般方法,包括在传感光纤表面镀薄敏感膜或者金属膜、优化传感光纤结构、进行荧光标记以及用纳米粒子修饰等一系列措施。     

消逝波激励及增益耦合的柱形微腔回音廊模激光辐射

毛细管的折射率比溶液的折射率高,石英毛细管在被插入的溶液中形成圆柱形微腔。采用近轴向消逝波抽运的方法,使激光的染料增益局限于抽运光在染料区的消逝场范围内,极大地提高了消逝波耦合柱形微腔的抽运效率。与侧向抽运方式比较,柱形微腔回音廊模(WGM)激光的抽运阈值从200μJ降低到9.5μJ。实验所得到的激光谱线波长以及相邻谱线的波数间隔与回音廊模式的理论计算吻合,说明石英毛细管能得到与石英光纤类似的柱形微腔回音廊模激光辐射。     

基于BOTDA的分布式光纤高温传感研究（特邀）

基于布里渊光时域分析（Brillouin optical time-domain analysis, BOTDA）测量技术分别研究了单模光纤、光子晶体光纤和镀金光纤在1100 ℃、1200 ℃和1000 ℃的高温传感特性,通过对石英光纤的布里渊频移（Brillouin frequency shift, BFS）跳跃现象和涂覆层燃烧现象进行研究,指出石英光纤均需要退火才能够达到热稳定状态。退火后,三种光纤的布里渊频移随温度呈非线性变化。其中,单模光纤和光子晶体光纤高温状态下涂覆层气化,二氧化硅发生晶化导致其机械强度大幅下降,因此仅能作为一次性高温传感器;镀金光纤由于金涂层具有较高的熔点和良好的气密性,高温退火后仍然能够保持良好的机械强度,因此可以作为一种重复使用的高温传感器。该研究有望为高温传感应用（如涡轮发动机内部温度监测）提供一种技术参考。     

Nanostructure Core Fiber With Enhanced Performances: Design, Fabrication and Devices

We report a new type of silica-based all-solid fiber with a 2-D nanostructure core. The nanostructure core fiber (NCF) is formed by a 2-D array of high-index rods of sub-wavelength dimensions. We theoretically study the birefringence property of such fibers over a large wavelength range. Large-mode-area (LMA) structure with a typical high birefringence in the order of $10^{-4}$ can be easily realized. The attenuation of the fabricated NCF is as low as 3.5 dB/km at 1550 nm. Higher macro- and micro-bending losses compared with those of the single-mode fiber (SMF) due to the reduced index difference have been observed experimentally, which suggests that the NCF is potentially useful for curvature and strain sensing applications. A fiber Bragg grating (FBG) inscribed in such a novel fiber is side-polished to make use of its evanescent field for refractive index sensing. The refractive index sensitivity obtained is one order of magnitude higher than that of the side-polished FBG in SMF, while the temperature and strain performances are comparable with those of the SMF-based FBG.      

1.3-μm GaInNAs-AlGaAs distributed feedback lasers

Room temperature continuous-wave operation of 1.3-μm single-mode GaInNAs-AlGaAs distributed feedback (DFB)-lasers has been realized. The laser structure has been grown by solid source molecular beam epitaxy (MBE) using an electron cyclotron resonance plasma source for nitrogen activation (ECR-MBE). Laterally to the laser ridge a metal grating is patterned in order to obtain DFB. The evanescent field of the laser mode couples to the grating resulting in single-mode DFB emission. The continuous wave threshold currents are around 120 mA for a cavity with 800-μm length and 2 μm width. Monomode emission with side-mode suppression ratios of nearly 40 dB have been obtained     

Control and suppression of power transfer in couplers by periodicindex modulation

The authors show that evanescent power transfer between the cores of a four-port single-mode coupler can be controlled by periodic modulation of the refractive indices in the cores. In particular, the effective coupling can be completely suppressed, provided the index modulation amplitude and period satisfy certain conditions     

Saturable absorption in a tapered single-mode optical fibre

A novel all-fibre saturable absorber based on the interaction between the evanescent field of a tapered single-mode fibre and a surrounding solution of a laser dye is described. Results are presented which demonstrate saturable absorption at pump powers of only tens of milliwatts.<>     

Single-mode-fibre passive components made in the fused-head-end technique

The fused-head-end technique, used successfully until now for producing passive fibre components in multimode fibre, can also be applied to produce single-mode fibre couplers and splitters. The device is based on evanescent mode coupling and has no pigtail problem. The first experimental results are presented, together with the theoretical interpretation. Some expected system applications and further improvements are indicated.     

Stabilized extrinsic fiber-optic Fizeau sensor for surface acousticwave detection

A surface acoustic wave sensor based on an in-line extrinsic Fizeau interferometer is described. A single-mode fiber, used as the input/output fiber, and a multimode fiber, used solely as a reflector, form an air-gap that acts as a low-finesse Fabry-Perot or Fizeau cavity. The Fresnel reference reflection from the glass/air interface at the front of the air-gap interferes with the sensing reflection from the air/glass interface at the far end of the air-gap. Strains in the thin-walled silica tube housing the two fibers change the length of the air-gap, thereby altering the phase difference between the reference and sensing reflections. A theoretical analysis of the interaction between the strain induced by elastic stress wave fields and the fiber sensor housing is presented     

A distributed fiber optic sensor based on cladding fluorescence

The fiber for the sensor is formed by cladding fused silica during drawing with polydimethyl siloxane into which an organic fluorescent dye, 9, 10-diphenylanthracene, has been dissolved. Upon side illumination at a wavelength within the excitation range of the dye, the cladding fluoresces; some of this fluorescence is coupled into guided modes in the fiber core through the evanescent fields of these modes. In the presence of oxygen, fluorescent emission by the dye is diminished. For the sensor described, the rubbery liquidlike nature of the polydimethyl siloxane cladding allows rapid diffusion of gases, and the intensity of the guided fluorescence is observed to drop by 30% in less than 5 s when the ambient atmosphere changes from pure nitrogen to pure oxygen. The advantages of this sensing technique, and some of the possibilities for new sensors based on this principle, are discussed     

基于光纤倏逝波传感器的磷酸根离子检测

提出了利用光纤倏逝波传感器通过光吸收方法来测量溶液中磷酸根离子浓度的新方法。将通信用标准单模光纤（SMF）局部腐蚀到接近芯层后放入不同浓度的磷钼蓝溶液中,当以磷钼蓝光吸收峰值为探测光波长时,光纤表面的倏逝波会部分被溶液吸收,通过测量光纤输出光强来计算溶液中的磷酸根离子浓度。实验结果表明,磷钼蓝溶液中磷浓度为0．04～O...