纳流通道-谐振腔耦合结构测量荧光物质微位移

本文提出了一种纳流通道-谐振腔耦合结构,用于实现对荧光物质微位移的检测。在本文中,首先,使用时域有限差分法,研究了量子点偏振态及结构参数对荧光与结构耦合效果的影响,进而对结构进行优化;然后,通过测量耦合结构输出光功率的变化,实现对荧光物质微位移的检测;最后,对影响传感灵敏度的因素进行研究。结果表明,相比传统方法,纳流通道-谐振腔耦合结构的折射率处于2.8~3.3之内时,该结构都可以实现对荧光物质微位移的高精度准确传感,并且通过减小纳流通道与谐振腔的间距可进一步提高传感灵敏度。     

长周期光纤光栅折射率传感器的结构优化

为了提高长周期光纤光栅对环境介质折射率的传感灵敏度,提出一种长周期光纤光栅的周期和包层半径的结构优化.基于长周期光纤光栅的耦合模理论,分析了长周期光纤光栅的周期和包层半径的大小分别与环境介质折射率传感灵敏度的关系,讨论了长周期光纤光栅的周期和包层半径对折射率传感的影响以及控制光栅周期与包层半径对折射率传感的重要性.为使...     

石英毛细管椭球微气泡模式特性及传感技术

利用有限元数值分析方法研究了椭球状石英毛细管微气泡回音壁模式特性及其折射率传感性能.计算分析了不同半径与内壁厚度情况下空芯和液芯椭球形微气泡模式特征,包括品质因数、有效折射率和能量比等,并探讨了微气泡在高灵敏度和高分辨率折射率传感方面的应用潜能.研究结果表明微气泡膨胀至350μm,且内壁厚度为1μm时分辨率和灵敏度最佳;在该厚度范围附近,微气泡分辨率不会因为半径尺寸的改变而发生太大变化;二阶径向模具有较高品质因数,其灵敏度略高于一阶基模,且使用二阶径向模可降低在制造时对结构壁厚控制精度的要求,可用于实际传感应用中.研究结果对微气泡的进一步实验研制具有理论参考价值.     

包层模谐振特种光纤及传感特性研究

研究了一种具有双包层结构的包层模谐振特种光纤,该特种光纤具有一个低折射率内包层,基于耦合模原理,纤芯模与包层模之间发生谐振耦合,从而获得具有带阻特性的传输光谱.系统介绍了包层模谐振光纤的制备、传输原理及其弯曲、溶液折射率、折射率/温度双参量等传感特性.实验和理论研究结果表明,包层模谐振特种光纤对于弯曲、溶液折射率参量具...     

微米光纤耦合型环境折射率传感器

本文展示一种由两根微米光纤构成的耦合型环境折射率传感器。微米光纤表面存在倏逝波,芯外介质折射率微小的改变将引起倏逝场分布变化,从而导致能量在耦合器两臂中的重新分配。本文通过测量耦合器两端出射光功率的比值来对葡萄糖溶液的浓度进行传感,实验结果表明该微米光纤耦合型传感器的浓度传感灵敏度可达1.58 mol·L~(-1)。本文用耦合模理论详细分析了两根相邻微米光纤的耦合效率与芯外介质折射率之间的关系,发现减小耦合区的光纤的直径,增大入射光波长或增大耦合长度,都可以进一步提高这种传感器的灵敏度。     

双S型光纤结构的传感特性

在剥除涂覆层的单模光纤上熔成两个间距为25mm的S型结构,构成双S型全光纤马赫-曾德干涉仪.入射光经过第一个S型结构时部分光被激发到包层,经过第二个S型结构时重新进入纤芯传播,S型结构中光纤的纤芯模和包层模耦合产生干涉.利用干涉光谱测量外界因素的响应并用于温度、折射率和微位移的测量.实验结果表明,温度、折射率和微位移的灵敏度分别为69pm/℃,132.64nm/RIU,-178pm/μm,且具有很好的线性度.该传感结构为全光纤结构,制作简单,易于实现且成本低.     

单挡板MDM波导耦合圆盘腔的Fano共振双模式特性研究

基于表面等离子亚波长结构的传输特性与光子局域特性,提出了一种单挡板金属-电介质-金属(MDM)波导耦合圆盘腔结构。由圆盘腔形成的两个孤立态与金属挡板形成的较宽的连续态干涉相消,形成两种不同模式的Fano共振。结合耦合模理论分析了该结构形成Fano共振的传输特性,用有限元分析法对结构进行模拟仿真,定量分析了结构参数对折射率传感特性的影响。结果表明:优化后的结构在两种模式下的优质因子分别为1.7×105和1.36×105,折射率灵敏度分别为710nm/RIU和1105nm/RIU,可为解决传感器在折射率测量时的交叉敏感问题提供理论参考。     

基于氧化铟锡的十重偏芯D型光子准晶光纤的高灵敏度表面等离子体共振传感器

设计并分析了一种高灵敏度表面等离子体共振(SPR)传感器,该传感器由偏芯D型结构的十重光子准晶光纤(PQF)组成,并局部涂覆氧化铟锡(ITO).偏芯D型结构可以使液体分析更加方便,增强了纤芯模与SPP模之间的耦合,提高了传感灵敏度.采用有限元法对传感器的特性进行研究.结果表明,传感器的波长灵敏度随折射率(RIs)的增大...     

长周期光纤光栅折射率传感器的结构优化

为了提高长周期光纤光栅对环境介质折射率的传感灵敏度,提出一种长周期光纤光栅的周期和包层半径的结构优化.基于长周期光纤光栅的耦合模理论,分析了长周期光纤光栅的周期和包层半径的大小分别与环境介质折射率传感灵敏度的关系,讨论了长周期光纤光栅的周期和包层半径对折射率传感的影响以及控制光栅周期与包层半径对折射率传感的重要性.为使优化的长周期光纤光栅具有实用性,谐振波长设计在1.55 μm的常规波长范围,经过多次摸拟实验,提出最佳优化参量为：Λ=380 μm,rcl=17 μm,对环境介质折射率从1.26~1.38不同值的实验测试,折射率传感灵敏度达到0.000 12,长周期光纤光栅的结构优化获得理想的预期效果.     

模间干涉的包层腐蚀型椭芯保偏光纤折射率传感特性

研究了一种基于模间干涉原理的微型椭芯保偏光纤的折射率传感特性。利用氢氟酸腐蚀的方法将椭芯保偏光纤制作成折射率灵敏的传感头,传感头可以根据控制腐蚀时间灵活控制其锥区结构。详细分析了保偏光纤内基模与一阶高次模模间干涉产生的双边瓣能量分布与被测折射率的关系,深入研究了锥区半径、工作波长对折射率灵敏度的影响。研究结果表明,光源波长为980 nm,折射率在1.39附近时,半径为8μm的传感头折射率灵敏度能够达到-7.1/RIU(即归一化光强与RIU之比,其中RIU为单位折射率)。     

Properties of the angular gap in a one-dimensional photonic band gap structure containing single negative materials

Properties of the angular gap in a one-dimensional photonic band gap structure containing single negative materials are investigated. This gap forms at oblique incidence due to the total internal reflection into air when the Snell's law breaks down. Its lower edge occurs at the frequency where the refractive index of one or both layers of the structure approaches zero. This gap is found to be highly sensitive to the incident angle and the polarization of the incident light, but is not affected by the thickness ratio of the layers. It is also shown that the electric field gets extremely enhanced at the lower edge of this gap for transverse magnetic polarization. This highly enhanced electric field can be utilized for certain applications.     

Terahertz multi-metal-wire hybrid-cladding hollow waveguide for refractive index sensing

We propose a design of terahertz refractive index sensing based on the multi-metal-wire(MMW) hybrid-cladding hollow waveguide. The proposed terahertz hybrid-cladding hollow waveguide comprises one air core in the center surrounding MMW surrounded dielectric. The central air core is used for filling lossless measurands and transmitting terahertz light. In particular, the refractive index sensing is realized by measuring the mode field area(MFA) variation of radially polarized mode. The modal effective refractive index, mode field intensity distribution, and mode field area properties responding to the measurand refractive indexes for different operating frequencies and structure dimensions are investigated, respectively.Simulations show that the proposed terahertz refractive index sensor can realize easily the measurement of the measurand refractive index. Meanwhile, the effects of operating frequency and structure parameters on sensitivity and measurement accuracy are also studied. In view of the trade-off between sensitivity and measurement accuracy, the reasonable choice of the operating frequency and structure parameters can optimize appropriately the sensitivity and measurement accuracy, and the sensitivity can reach approximately 0.585 mm~2/RIU(RIU is short for refraction index units) with the proper frequency and structure parameter.     

空气孔辅助光纤的模式截止

光纤的截止波长是光纤设计的重要参量之一。利用全矢量正交函数模型对空气孔辅助光纤的模式截止特性进行了讨论。分析表明：由于光纤包层中存在空气孔,即使不考虑材料色散,包层的有效折射率也与波长有关;包层有效折射率由包层中空气孔的大小和波长决定,与芯子的掺杂浓度无关。在所研究的波长范围之内,与传统的w型光纤类似,在包层中空气孔的相对尺寸d／Λ较大时出现了基模截止现象。d／Λ从0．2到0．9变化时,光纤的各阶模式的截止波长都随之减小;各阶模式的截止波长随d／Λ变化曲线的斜率随模式阶次的升高而降低。     

Effective refractive index for determining ray propagation in an absorbing dielectric particle

The ray-tracing technique can be employed to simulate the scattering of light by a dielectric particle whose characteristic dimension is much larger than the incident wavelength. When a scattering particle is absorptive, a localized electromagnetic wave refracted into the scatterer is inhomogeneous, which requires the use of an effective refractive index to determine the propagation direction of the refracted ray. The effective refractive index for the first-order reflection–refraction event (i.e., the case for the ray-transmission from air into a particle) has been previously derived by the authors. In this study, we further develop recurrence formulae for the effective refractive indices associated with higher-order reflection–refraction events when the ray-transmission is from a particle to air. It is shown from the new formulae that effective refractive indices in this case depend upon ray history. Numerical results indicate that the real and imaginary parts of the effective refractive index are larger and smaller, respectively, than the real and imaginary parts of the inherent complex refractive index of an absorbing particle. Furthermore, if the particle faces associated with two sequential internal reflections are parallel to each other, the corresponding effective refractive indices are the same.     

Near-field measurement of amplitude and phase in silicon waveguides with liquid cladding

Heterodyne near-field scanning optical microscopy (H-NSOM) has proven useful as a tool for characterization of both amplitude and phase of on-chip photonic devices in air, but it has previously been unable to characterize devices with a dielectric overcladding, which is commonly used in practice for such devices. Here we demonstrate H-NSOM of a silicon waveguide with a liquid cladding emulating the solid dielectric. This technique allows characterization of practical devices with realistic refractive index profiles. Fourier analysis is used to estimate the effective refractive index of the mode from the measured data, showing an index shift of 0.08 from air to water cladding, which is seen to correspond well to simulations.     

Low-cost,high performance surface plasmon resonance-compatible films characterized by the surface plasmon resonance technique

A new analytical method based on the surface plasmon resonance (SPR) technique is presented, with which SPR curves for both wavelength and angular modulations can be obtained simultaneously via only a single scan of the incident angle. Using this method, the SPR responses of TiO2-coated Cu films are characterized in the wavelength range from 600 nm to 900 nm. For the first time, we determine the effective optical constants and the thicknesses of TiO2-coated Cu films using the SPR curves of wavelength modulation. The sensitivities of prism-based SPR refractive index sensors using TiO2-coated Cu films are investigated theoretically for both wavelength and angular modulations, the results show that in the case of sensitivity with wavelength modulation, TiO2-coated Cu films are not as good as the Au film, however, they are more suitable than the Au film for SPR refractive index sensors with angular modulation because a higher sensitivity can be achieved.     

Reflex optical sensor based on dual metal gratings with high angular sensitivity

An interesting reflection phenomenon in a dual metal grating (DMG) structure is studied, which is related to the competition between Fabry-Prot (F-P) resonance effect and evanescent-field coupling effect inside the gap between the two composing single metal gratings. This competition leads to high angular sensitivity in response to the refractive index variation of the sample solution in the gap. A reflex optical sensor with high sensitivity based on DMG for detecting the change in refractive index is proposed and its performance theoretically is discussed.     

Influence of oxygen on the guiding properties of V2O5-clad glass waveguide

An optical waveguide clad with V2O5 is proposed as a new type of oxygen sensor in ambient air. The presence of gas changes the light transmission (TE0-polarized mode) through the guide, due to the change in refractive index of the cladding which changes the effective index of the guide. O2 gas concentration is varied from a few (≈10) ppm to several percent (4%). Sensors exhibit the same sensitivity at a slightly elevated temperature. The increase in thickness of the cladding causes a reduction in sensitivity and increase in linearity. It is observed that the sensor exhibits the same performance using the static or incremental mode. This revised version was published online in November 2006 with corrections to the Cover Date.     

微纳光纤布拉格光栅折射率传感特性研究

利用光纤布拉格光栅方程和光纤基模有效折射率随纤芯半径和环境折射率的函数关系, 建立了微纳光纤布拉格光栅(MNFBG)反射波长随环境折射率变化的数学模型, 给出了波长灵敏度函数, 并指出MNFBG反射波长的变化规律决定于有效折射率随纤芯半径和环境折射率变化的关系. 详细探究了有效折射率及其灵敏度的变化规律, 结果表明: 有效折射率随纤芯半径和环境折射率的减小而非线性减小, 其对环境折射率变化的灵敏度随环境折射率的增大而非线性增加, 而且随纤芯半径减小, 有效折射率的灵敏度、线性度以及线性响应范围均呈递增规律. 通过对纤芯半径为0.5 μm的MNFBG在1.20–1.30和1.33–1.43 环境折射率范围内的波长响应关系拟合, 分别获得了477.33 nm/RIU和856.30 nm/RIU的波长灵敏度以及99.58 %和99.7%的高线性度, 论证了分析结论以及折射率区间划分测量方案的正确性, 为MNFBG折射率传感器的设计、优化以及应用提供了参考依据. 关键词： 微纳光纤 光纤布拉格光栅 折射率传感 数值模拟     

Study on optical gain of one-dimensional photonic crystals with active impurity

Localized fields in the defect mode of one-dimensional photonic crystals with active impurity are studied with the help of the theory of spontaneous emission from two-level atoms embedded in photonic crystals.Numerical simulations demonstrate that the enhancement of stimulated radiation, as well as the phenomena of transmissivity larger than unity and the abnormality of group velocity close to the edges of photonic band gap, are related to the negative imaginary part of the complex effective refractive index of doped layers. This means that the complex effective refractive index has a negative imaginary part, and that the impurity state with very high quality factor and great state density will occur in the photonic forbidden band if active impurity is introduced into the defect layer properly. Therefore, the spontaneous emission can be enhanced, the amplitude of stimulated emission will be very large and it occurs most probably close to the edges of photonic band gap with the fundamental reason, the group velocity close to the edges of band gap is very small or abnormal.