空心微瓶谐振腔的封装及折射率传感特性研究北大核心CSCD

为提高传感器的稳定性和便携性,提出一种基于空心微瓶谐振腔的折射率传感器,对系统进行封装并对其折射率传感特性进行研究。仿真分析不同壁厚下空心微瓶谐振腔径向回音壁模式的光场分布,光场在微瓶内部的占比随着器件壁厚的减少而增加,有利于提高传感灵敏度。为减小空心微瓶谐振腔的壁厚,利用氢氟酸对石英毛细管进行腐蚀,使用光纤熔接机制备了薄壁空心微瓶谐振腔。采用紫外胶将耦合系统封装固定在载玻片上,器件稳定性和便携性得到提升。研究了封装器件在不同折射率匹配液下的传感特性,器件传感灵敏度为26.50 nm/RIU。该传感器具有稳定性强、灵活性高、损耗小等优点,在光微流控折射率检测方面拥有很大的应用潜力。     

表面等离子体激元微盘的优化设计及应用

表面等离子体激元(SPP)微腔具有很高的品质因子和极小的模式体积,在光电子器件研究方面具有重要的应用价值。采用有限元法对表面等离子体激元的金属覆盖介质微盘谐振腔进行理论模拟,研究考虑微盘底半径、介质层厚度及金属膜厚度等参数对微盘表面等离子体模的品质因子及模体积的影响。研究表明,在光通信波段1550nm附近获得高品质因子(1000以上),极低模式体积的表面等离子体微盘。最后研究了利用优化设计的微盘进行折射率传感的应用,获得了高达300nm/RIU的折射率传感灵敏度。     

工字形太赫兹超材料吸波体的传感特性研究

利用超材料吸波体对材料参数的电磁响应, 可将其应用于传感. 本文设计了一种工字形单元结构的超材料吸波体, 基于频域算法对其在太赫兹频段的传感特性进行数值模拟, 研究了待测样品折射率、厚度及电介质隔层厚度对超材料吸波体传感器的频率灵敏度、振幅灵敏度及品质因数的影响. 研究结果表明:当待测样品厚度为40 μm时, 折射率频率灵敏度可达到153.17 GHz/RIU, 折射率振幅灵敏度可达到41.37%/RIU; 待测样品折射率一定时, 厚度频率灵敏度随其厚度的增大而线性减小; 随着待测样品厚度的增加, RFOM呈增大趋势, 但增大幅度在逐渐减小; TFOM随待测样品厚度的增加而减小.     

具有内参考热补偿功能的三层膜结构微球腔折射率传感器

tBtB光学微腔在高灵敏度传感中有着重要的应用前景,而在传感中热漂移是制约其走向实用的重要因素.本文提出了一种镀有三层膜结构的微球腔,可以在实现高灵敏度折射率传感的同时,具备内参考热补偿功能.该结构由内到外分别涂覆折射率为高、低、高的薄膜,内外两高折射率层可以分别支持各自的回音壁模式,称之为内层模式和外层模式.研究了波导耦合的内外模式在折射率传感和温度传感应用的表现.结果表明,中间膜层厚度为550 nm时,内外模式的折射率灵敏度分别为0.0168和102.56 nm/RIU,温度灵敏度分别为–19.57和–28.98 pm/K.通过监测内外模式谐振波长的差值进行传感,对中间膜层厚度进行优化,=400 nm时,折射率灵敏度为75.219 nm/RIU,探测极限可以达到2.2×10~(–4) RIU,热漂移被减小到3.17 pm/K,极大地减小了热漂移对系统的影响.本研究可为微球腔折射率传感器的设计和改进提供指导.     

基于游标效应的高灵敏度光纤耦合器折射率传感器

为解决传统光纤折射率传感器灵敏度较低的问题,提出一种基于游标效应增强的拉锥光纤耦合器折射率传感器。利用拉锥光纤耦合器的双折射效应,在耦合器中形成x偏振态和y偏振态两路模式(奇模与偶模)干涉,两路略有差别的干涉通过叠加,形成游标效应。通过理论分析和数值计算,发现当拉锥耦合器的宽度为1.6～3.2μm时,奇模与偶模的群双折射系数差值会出现零点,折射率传感器的灵敏度会得到显著增强。在理论分析和数值仿真的基础上,实验研究了宽度为1.6μm的光纤耦合器的折射率传感性能,并在折射率1.333附近获得了30020.0nm/RIU和-34402.5nm/RIU的超高灵敏度。该传感器制作简单、结构紧凑且成本较低,在高灵敏度生物医学检测和分析化学领域具有重要应用前景。     

光纤锥在线型马赫-曾德干涉仪的折射率传感特性

提出了一种基于光纤锥的在线型光纤马赫-曾德干涉仪式折射率传感器.传感器是在一根单模光纤上使用光纤熔接机拉制出两个光纤锥,光纤锥的直径为43.7μm,长度为480μm.干涉仪中光纤锥充当光纤耦合器,激发出光纤高阶模,并将高阶模耦合进单模光纤使之与纤芯基模形成模间干涉.被环境溶液的折射率、温度的变化改变模式间相位差,将导致干涉仪的传输光谱发生漂移,从而实现传感测量.实验结果表明:当环境溶液的折射率变化范围为1.335~1.403RIU时,传感器的折射率灵敏度为-128.233nm/RIU;当水溶液的温度变化范围为30~75℃时,传感器的温度灵敏度为0.111nm/℃.该传感器具有制作方法简单、灵敏度高、成本低等特点,可应用于生物传感测量.     

一种基于模间干涉的亚波长直径光纤气体折射率传感

设计了一种基于模间干涉的亚波长直径光纤气体折射率传感方案,并分析了其测量灵敏度.将标准单模光纤和一段仅传输基模与二阶模的无包层亚波长直径光纤结合形成传感头,通过分析传感头外气体折射率的变化对两个模式干涉谱峰值移动的影响,研究了这种传感器的折射率测量灵敏度.结果表明,这种传感器的灵敏度高于利用折射率引导型光子晶体光纤的基于模间干涉的折射率传感器.因为没有气体向微孔扩散的过程,这种基于模间干涉的亚波长光纤折射率传感器可用于实时探测.     

高Q值薄壁液芯毛细管微腔电场传感器

为提高电场传感器的抗电磁干扰能力、灵敏度和稳定性,将高Q值薄壁液芯毛细管微腔和电泳效应结合,增强回音壁模共振微腔对外加电场的感知能力,并进行了实验验证.基于时域有限差分法得到了液芯毛细管微腔回音壁模式共振特性随毛细管直径、壁厚等结构参数的变化规律,发现随着壁厚变薄灵敏度增加.采用熔融拉锥法制备了直径为86μm,壁厚约为2μm的薄壁毛细管微腔,通过高精度位移平台实现了锥形光纤和毛细管微腔的高效率耦合,测得回音壁模式Q值为2.8×10^6.毛细管微腔内注入不同浓度的蛋白质溶液,利用电泳原理和蛋白质分子在缓冲溶液里带电的特性,实现的最大电场传感灵敏度为10.6 pm/(kV/m).     

一种基于模间干涉的亚波长直径光纤气体折射率传感

设计了一种基于模间干涉的亚波长直径光纤气体折射率传感方案,并分析了其测量灵敏度.将标准单模光纤和一段仅传输基模与二阶模的无包层亚波长直径光纤结合形成传感头,通过分析传感头外气体折射率的变化对两个模式干涉谱峰值移动的影响,研究了这种传感器的折射率测量灵敏度.结果表明,这种传感器的灵敏度高于利用折射率引导型光子晶体光纤的基于模间干涉的折射率传感器.因为没有气体向微孔扩散的过程,这种基于模间干涉的亚波长光纤折射率传感器可用于实时探测.     

基于椭球封闭空气腔的光纤复合法布里-珀罗结构折射率传感特性研究

提出了基于微椭球型空气腔的在线型光纤复合法布里-珀罗干涉结构,并对其折射率传感特性进行了研究.椭球型空气微腔是利用光纤熔接机对实芯光子晶体光纤和单模光纤以特定的熔接参数熔接形成.用高斯光束模型和ABCD法则分析了椭球型空气腔的腔内损耗,建立了电磁场在复合法布里-珀罗干涉结构中传播的物理模型.根据腔长比值的不同,环境折射率对干涉条纹的影响有对比度调制和波长调制,主要研究了一种波长调制型复合法布里-珀罗结构折射率传感器.仿真结果表明该折射率传感器在1—1.6范围内不出现折射率转折点;实验结果表明在1.333—1.466范围内,折射率灵敏度～37.088 nm·RIU-1,分辨率约为2.69×10-5.该光纤复合法布里-珀罗结构干涉条纹对比度高、体积小、成本低,用于折射率测量可靠性高、分辨率高、无折射率拐点、温度串扰小.     

Structure design of refractive index sensor based on LPFG with double-layer coatings

Based on the coupled-mode theory, the mode transition and transmittance of LP modes in an LPFG with double-layer coatings are studied theoretically. As a refractive index sensor, this LPFG structure is designed for high sensitivity by selecting a suitable thickness and refractive index of the double-layer coatings. Date simulation indicates that the effective index of the LP cladding mode increases in steps with the first coating thickness, thus LP mode is guided to the overlay and the mode transition takes place, where the LP modes can be easily affected by the ambient. Thereby, the coated LPFG sensor should be designed to operate at the transition region. In addition, the effective refractive index of LP cladding modes also increases in steps with the refractive index of the second overlay. For the higher order LP modes, the transition regions are broaden and the dynamic responses are greater than the lower LP modes, which means the higher order LP modes can be used for lower index overlay sensing. Further, the transmittance spectrum, sensitivity and measurable dynamic range of this LPFG are analyzed. The sensitivity of the LPFG sensor is available to $10^{3}$ with suitable overlay thickness and measurable dynamic range of the sensitive film refractive index is available to $10^{-2}$ . So the presented LPFG sensor enhances the design flexibility and enlarges the scope of application, which will likely be developed for high sensitivity LPFG sensors.     

Numerical modeling of microbubble backscatter to optimize ultrasound particle image velocimetry imaging: initial studies

We have developed a promising non-invasive ultrasound-based method for performing particle image velocimetry (PIV) in vivo. This method, termed echo PIV, provides multi-component blood velocity data with good (2 ms) temporal resolution. The method takes advantage of the non-linear ultrasound backscatter characteristics of small gas-filled microbubbles (ultrasound contrast) that are seeded into the blood stream. In this study, we use a numerical model to explore potential areas to focus future work in echo PIV.

Ultrasound backscatter from encapsulated microbubbles was modeled using a modified Rayleigh–Plesset equation (Church model, 1995), taking into account the protein/lipid shell layer as a thick, mass-conserving incompressible fluid surrounded by incompressible blood-like fluid. The equation of motion was solved numerically to characterize the fundamental and second harmonic components of the backscattered pressure. Results show a significant advantage in using the second harmonic component for echo PIV, especially for small bubble sizes less than 3 μm in diameter at 2.2 MHz frequency. The effect of the shell thickness ranging from 10 to 500 nm on the vibration amplitude of the bubble was examined and it is shown that the presence of the shell requires mechanical index (MI)>0.2 of incident pressure amplitude to improve bubble detectability. Analysis of the effect of pulse length shows a tradeoff between axial resolution (short pulse length) and bubble detectability (longer pulse length) will most likely be required. The effect of varying MI between 0.1 and 0.6 was also studied at a center frequency of 2.2 MHz and the results indicate that the resonance of the second harmonic is maximized for bubbles with diameter of approximately 2.75 μm. Bubble non-linearities at MI>0.2 induced a resonant frequency shift away from the integer multiple of the incident frequency in the second harmonic backscatter. For a given bubble size, there is a combination of optimal incident frequency and mechanical index range that maximizes the ratio of the second harmonic compared to the fundamental. This resonant frequency decreases with increasing bubble radius. Further, a narrow bandwidth pulse is shown to increase signal strength. Both of these effects may cause conflict with factors governing spatial resolution. Optimization of the incident frequency, microbubble size and mechanical index to enhance bubble detectability will depend on the particular clinical application. These theoretical predictions provide further understanding of the physics behind our echo PIV technique, and should be useful for guiding the design of echo PIV systems.     

基于包层模的光纤布拉格光栅折射率传感特性

提出了基于光纤布拉格光栅(FBG)包层模式的折射率传感方案。实验中,利用不同浓度的丙三醇水溶液作为外界折射率传感溶液,采用氢氟酸溶液化学腐蚀的方法来减小光纤包层的直径以增大包层模式对外界折射率的敏感度,研究了腐蚀后光纤布拉格光栅包层模式的耦合波长对外部折射率的变化关系。实验结果表明在1.3300~1.4584的折射率范围内,包层模式耦合波长随外界折射率增大而增大,在接近光纤包层折射率处具有很高的折射率灵敏度,最大达到了172 nm/riu(refractive index unit)。而且,包层模谐振的光谱半峰全宽(约0.07 nm)仅为布拉格纤芯模谐振光谱半峰全宽的1/4,能够获得更好的传感精度。     

镀高折射率纳米膜的长周期光纤光栅特性研究

针对镀高折射率纳米膜的长周期光栅,建立了传感理论模型,研究了长周期光栅的谐振波长与纳米膜厚度及外界折射率的关系,给出不同纳米膜厚度下长周期光栅不同包层模式重组特性.研究发现,当长周期光栅外面镀上一层沿角向均匀分布的纳米膜时,随着膜厚变化会出现包层模分布的明显调制;适当选择镀膜参数和外界介质折射率,最低次包层模式HE1,2会成为镀膜层中的导模,其他的包层模式将会发生模式转换现象;对于较低次包层模式(如HE1.6),在模式转换的时候存在两步转换,而高次的包层模只有一步转换(如HE1.14).同时给出了包层模式转换对外界折射率响应的关系:当膜层厚度增加时,长周期光栅模式转换现象移至低折射率区域.     

用迈克尔逊干涉仪测量全息干板膜厚度

全息干板膜的厚度是全息干板的重要参数之一。使用迈克尔逊干涉仪和白光光源对2种全息干板膜厚度进行测量，并对测量结果误差进行分析，给出了测量误差与膜厚及折射率之间的关系以及此方法的适用范围。研究结果表明：在膜厚从8μm增至41μm的过程中，测量结果的绝对误差≤2μm且变化很小，相对误差则从14.1%降到了2.2%。随着膜厚的增加，相对误差明显降低；折射率n也参与了误差传递，其值与测量误差呈类似反比关系；当n值在1.5附近时，为保证测量的准确性，所测膜厚≥40μm。最后指出，迈克尔逊干涉仪在测量全息干板膜等较厚的薄膜时，具有测量范围大，结果较准确等优点。     

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     

Optical microfiber mode interferometer for temperature-independent refractometric sensing

We report on a functional optical microfiber mode interferometer and its applications for absolute, temperature-insensitive refractive index sensing. A standard optical fiber was tapered down to 10 μm. The central part of the taper, i.e., the microfiber, is connected to the untapered regions with two identical abrupt transitions. The transmission spectrum of our device exhibited a sinusoidal pattern due to the beating between modes. In our interferometer the period of the pattern-an absolute parameter-depends strongly on the surrounding refractive index but it is insensitive to temperature changes. The period, hence the external index, can be accurately measured by taking the fast Fourier transform (FFT) of the detected interference pattern. The measuring refractive index range of the device here proposed goes from 1.33 to 1.428 and the maximum resolution is on the order of 3.7×10(-6).     

Photonic crystal fiber tip interferometer for refractive index sensing

In this paper we present an interferometer based on photonic crystal fiber (PCF) tip ended with a solid silica-sphere for refractive index sensing. The sensor is fabricated by splicing one end of the holey PCF to a single mode fiber (SMF) and applying arc at the other end to form a solid sphere. The sensor has been experimentally tested for refractive index and temperature sensing by monitoring its wavelength shift. Measurement results show that the sensor has the resolution of the order of 8.7×10(-4) over the refractive index range of 1.33-1.40, and temperature sensitivity of the order of 10 pm/°C in the range of 20-100 °C.