Simultaneous measurement of refractive index and temperature based on a long period fiber grating inscribed in a photonic crystal fiber with an electric-arc discharge

A novel fiber sensor composed by two single mode fibers and long period fiber grating based on a photonic crystal fiber prepared by periodic discharge heating has been experimentally investigated to measure refractive index and temperature. A Mach-Zehnder interferometer was formed due to the presence of two fusion spliced collapsed regions in the photonic crystal fiber. The resonance dip and interference pattern were differently influenced by the ambient disturbance, so the dual-parameters were simultaneously measured by analyzing the characteristics of transmission spectrum. After the experimental measurements, refractive index and temperature sensitivities of 117.28?nm/RIU and ?86.29?pm/°C were realized. Therefore, the reported sensor with advantages of easy fabrication, simple structure, and small size has the potential for simultaneous refractive index and temperature measurements involving biochemical sensing applications.     

A NOVEL ALL-FIBER ELECTRIC FIELD SENSOR BASED ON TAPERED FIBER-SLAB WAVEGUIDE COUPLER

□ A novel optical electric field sensor based on evanescent coupling between a tapered fiber and a slab waveguide is proposed and demonstrated. Light in a tapered fiber evanescently couples into the slab waveguide and forms a wavelength resonant spectrum. A slice of a LiNbO₃ crystal was used as the slab waveguide. External electric fields may change the refractive index of the crystal and thus make the resonant wavelengths shift. Therefore, an optical electric field sensor was obtained by measuring the wavelength shift caused by an external electric field. The principles and design of the proposed sensor are reported. The performance of the proposed sensor are demonstrated experimentally by detecting sinusoidal fields with 50 Hz and pulsed electric fields with a rise time of 1.2µs. The results show that the minimal detectable field was approximately 150 V/cm with a signal-to-noise ratio of three.     

Graphene-based optical fiber ammonia gas sensor

To precisely monitor and forecast harmful gases in the air, a high-performance fiber gas sensor based on graphene nanometer-functional materials is proposed and experimentally demonstrated. The sensing area of the proposed sensor was a graphene-wrapped fiber which was cascaded between a down-taper and an up-taper. The graphene wrapping on the subuliform fiber sensing area substantially increased the evanescent field which transmits along the surface of fiber and will have a significant sensitization effect on the gas sensing. At the same time, the gas molecules adsorbed by graphene lead to changes of the effective refractive index of the composite waveguide, which causes corresponding wavelength drift and attenuation. By detecting the change of the output optical signal, the concentration of gas molecules was detected. Based on this principle, the sensor realized a gas sensitivity of 0.015?nm/ppm. The research shows that the sensing structure has the advantages of small volume, good mechanical strength, excellent spectral quality, and high sensitivity.     

基于微环谐振器的溶液浓度传感器研究

设计了基于微环谐振器的溶液浓度传感器,提出了一种溶液浓度测量的新方法。介绍了全通微环谐振器(MRR)的结构及传输机制和MRR浓度传感器的工作原理。根据电磁场理论得到了狭缝波导的特征方程,计算了MRR的共振波长,并以乙二醇溶液为例,利用有限时域差分法模拟了外界环境浓度变化时微环的功率谱。模拟结果表明:随着乙二醇溶液浓度增大,MRR的谐振波长与乙二醇溶液浓度的变化近似呈线性关系,与理论计算结果一致;并对该传感器的灵敏度进行计算,结果显示灵敏度可达490.2nm/RIU。采用MRR测量液体浓度成本低、结构简单,能够实现对环境介质的快速精确测量。所设计传感器还可用于测量固体、气体浓度和其它与浓度、折射率相关的参量。     

基于Cantor结构的一维光子晶体耦合腔的光学特性

在N=3的三分Cantor多层结构的基础上设计了一种光子晶体耦合腔结构,用传输矩阵法研究了这种耦合腔结构的光学特性。结果表明,新结构有更宽的带隙,并在宽带隙中出现了一个损耗非常小的超窄透射窗口;保持缺陷层的几何厚度不变,改变缺陷层介质的折射率,该透射窗口位置能在很大的范围内移动。这种新的耦合腔结构可用作超窄带光子晶体滤波器或波长可调谐滤波器,在光通信超密集波分复用和光学精密测量等领域中有应用价值。     

基于正四边形晶格的微结构光子晶体光纤的特性分析

设计了基于正四边形晶格空气孔排列的光子晶体光纤,并在此基础上,通过在纤芯附近引入不同的微结构空气孔,运用全矢量有限元差分法,对不同微结构的光子晶体光纤的模式有效折射率、限制损耗、模场有效面积、非线性系数、波导色散系数等特性参数进行了仿真与分析。结果表明:引入不同的微结构,可以减小有效模场面积和增大非线性系数;引入正四边形微结构空气孔时,其限制损耗整体变化幅度较小;引入正八边形微结构空气孔时,其对应的波导色散系数在中波段变化比较平坦,且在波长为1 550nm处波导色散系数接近于零;引入正十二边形微结构空气孔时,其波导色散系数均为负值且变化幅度不大,可以应用于光纤的色散补偿。根据对引入不同微结构的光子晶体光纤的特性研究,为进一步研究光子晶体光纤提供一定的参考。     

基于光子晶体和法布里珀罗腔结构的折射率传感器

光子晶体传感器在溶液检测方面具有巨大的应用潜力,设计一种光子晶体液体折射率传感器,通过在光子晶体中构造法布里珀罗腔(F-P腔)并利用光子晶体的自准直效应来实现折射率的探测。通过二维时域有限差分法(2D-FDTD)对电磁波在光子晶体F-P腔中的传播的仿真实验,最终获得了高线性度的输出光功率与液体折射率的对应关系,并可基于此特性实现液体折射率的检测。相较于其他的检测方法,光子晶体的应用使其具有体积小、测量范围广、易于与激光器件集成并且不受外界电磁环境影响等优点。     

四边形周期结构负折射介质光子晶体光纤的设计

提出了一种纤芯与介质柱为负折射率材料、衬底为正折射率材料的新型四边形周期结构光子晶体光纤(PCF)。介绍了它的结构设计,研究了光子带隙效应导光特性。与传统四边形周期结构光子晶体光纤相比,该种光纤可以实现带隙效应导光传输,取填充比f=0.7时可获得光子带隙传输范围为880~4140nm,可应用于远红外光通信中。     

Evanescent-field photonic microcells and their applications in sensing

This paper reports the results of our recent studies on evanescent-field photonic microcells (PMCs) made by post-processing commercial micro-structured optical fibers and by encapsulating tapered micro/nano fibers within glass capillaries. The PMCs have a wavelength/sub-wavelength scale wave-guiding core housed within a miniature hollow compartment. The housing isolates the waveguide core from external contamination and provides a robust platform for efficient evanescent field interaction with the materials filling the compartment. The techniques for fabrication are described and the applications of the PMCs for sensing temperature, gas pressure, refractive index and mechanical acceleration are discussed.     

二维光子晶体光波导透射特性的研究

用时域有限差分方法(FDTD)研究光波在光子晶体光波导中的传播规律,发现不同形状的波导能够导引不同频率的光波。光子晶体波导的带隙宽度和透射系数与该波导的结构和参数都有很大的关系,随着介质柱半径的变化,带隙呈现一定的变化规律,介质柱半径变小,该波导的带隙向高频方向移动,且带隙的宽度变宽;而介质柱半径变大时,光波的透射峰的峰值却变得比较大,损耗变小。研究结果为光子器件的设计提供了理论依据。     

开环光子晶体光纤化学传感器的设计

为了提高低折射率化学物质监测的灵敏度,采用光子晶体光纤设计了一种在开环内镀有金薄膜的表面等离子体共振传感器。利用仿真软件COMSOL Multiphysics 5.6系统地研究了开环半径、内部气孔大小、金属膜层厚度对该传感器灵敏度的影响。最终在2800～4700 nm的工作波段内设计出折射率检测范围为1.26～1.31的低折射率传感器。该传感器平均灵敏度高达22 500 nm/RIU,最高灵敏度达33 000 nm/RIU。在七氟醚、卤代醚、含氟有机物等低折射率物质检测方向具有较好的应用前景。     

全角度反射的多层介质膜系

在总结金属反射镜及多层介质反射镜的优缺点的基础上 ,按照一维光子晶体的设计思想 ,提出用λ/4膜系设计特定波长范围内的全偏振全角度反射镜的方法 ,给出了反射带中心波长、边缘波长及带宽的表达式 ,并对如何避免 Brewster窗作了定量分析。     

Simultaneous measurement of refractive index and temperature by integrating an external Fabry-Perot cavity with a fiber Bragg grating

A fiber sensor for simultaneous measurements of refractive index and temperature based on the integration of a fiber Bragg grating (FBG) with an external Fabry-Perot (F-P) cavity is presented. The fringe contrast of the interference spectrum generated by the F-P cavity is used to determine the external refractive index, while the wavelength shift of the FBG is used to measure temperature. The result showed that the refractive index and temperature sensitivity for the integrated sensor is 8.1 × 10(-6) and 0.01006 nm/°C, respectively.     

Theoretical Research on Optofluidic Photonic Crystal Waveguide for Broadly Tunable and Ultra-Wideband Slow Light

Broadly tunable and ultra-wideband slow light was theoretically demonstrated in a line defected photonic crystal waveguide (PCW) by infiltrating fluid with suitable refractive index into the first row of air holes adjacent to the waveguide. Simulation results showed that the working wavelength of the flat slow light in the optimized optofluidic PCW could be tuned from 1542.5 nm to 1569 nm with nearly constant group index of 80. Namely, broadly tunable slow light could be realized with the ultra-wide bandwidth over 26.5 nm and the group index up to 80. These achievements could not only open the possibility for achieving many excellent optical devices based on slow light in PCW, but also highlight the versatility, flexibility, and tunability offered by optofluidic infiltration schemes.     

High sensitivity internal refractive index sensor based on a photonic crystal fiber long period grating

A high sensitivity method is reported for the measurement of the internal refractive index using a photonic crystal fiber long period grating. Long period gratings of different lengths were inscribed in photonic crystal fibers, and the air holes of the fiber had varying refractive indices. A side lobe appeared near the resonant dip through the analysis of the characteristics of transmission spectra showing variation in the refractive index. The resonant dip and its side lobe provided varying sensitivities to the internal refractive index values. The sensitivity of the side lobe was as high as 2343?nm/refractive index unit (RIU), which exceeded the value for the resonant dip (2047?nm/RIU) for refractive indices from 1.3333–1.3792. Due to the high resolution of 8.5?×?10^?6 RIU, this method offers promising applications for biological and chemical analysis in which high-precision refractive index measurements are required.     

基于亚波长光栅的负折射光子晶体成像研究

理论上折射率为?1的平板超透镜可以实现完美成像,但等效折射率为?1的光子晶体结构,不满足介电常数ε=?1和磁导率μ=?1的条件,光子晶体与自由空间阻抗不匹配,某些角度的入射光与光子晶体内布洛赫波不能耦合,致使该空间频率光信息丢失,限制了光子晶体成像分辨率.为了提高成像分辨率,在光子晶体表面设置亚波长光栅结构,利用光栅的...     

多信道二维光子晶体滤波器

根据光波模在光子晶体线缺陷波导和环形谐振腔之间的耦合原理,在二维三角晶格光子晶体中设计了一款由线缺陷主波导、环形谐振腔、60°弯下载波导组成的多信道下载滤波器。利用平面波展开方法计算了完整光子晶体及线缺陷波导的能带结构;基于时域有限差分方法计算了各目标频率光信号在器件中的传输特性,分析了影响器件耦合效率的因素并对其进行了改进。分析表明:通过改变环形谐振腔内介质柱的半径可以调节光子晶体环形谐振腔的谐振频率,而改变线缺陷主波导与环形谐振腔之间耦合区域中介质柱的形状以及将直下载波导改换成60°弯下载波导可以提高线缺陷主波导、60°弯波导与环形谐振腔之间的耦合效率。计算结果显示:优化后的多信道二维光子晶体滤波器具备优良的选频功能,各目标频率光信号的透射率均达90%以上。与传统半导体介质材料器件相比,该器件体积较小,结构简单,易于大规模集成,很有应用前景。     

太赫兹波段光子晶体温度传感器的研究

使用对太赫兹波段有吸收效应的掺杂硅设计光子晶体结构,使得在光子带隙内的光波被吸收,并加上金属反射镜面将光子晶体的吸收峰和法布里-珀罗(F-P)谐振吸收峰结合,使此结构在0.29～0.31 THz波段达到宽频吸收,并且在0.31～0.34 THz波段通过测量光子晶体的反射率可以计算出对应温度。在使用商业电磁仿真软件CST2014仿真和优化参数后,反射率对应温度变化的变化范围是0.09～0.36,即最大值与最小值有4倍之差,这一特性表明,此结构的反射率变化随温度变化十分明显,是一款十分灵敏的温度传感器。此外,在入射角不大于40°时,结构性能依然良好。     

基于同轴光子带隙晶体的应变传感器

基于微波网络理论,提出了一种基于变绝缘层的同轴光子带隙晶体应变传感器的设计方法。给出了同轴光子带隙晶体传感器的结构形式,推导了传感器带隙极值频率与晶体电长度之间的关系。根据给定监测频点设计了传感器的几何尺寸及材料参数,计算了传感器的S参数,计算结果与仿真结果相吻合。分析了提高该传感器灵敏度和品质因数的方法,并搭建了实验测试平台。实验结果表明:当应变量由0με提高至10 000με时,极值频率由2.450GHz移至2.432GHz,频移量为18 MHz,灵敏度为1.8kHz/με。得到的实验结果与仿真结果相吻合,验证了本文所提出的基于变绝缘层的同轴光子带隙晶体应变传感器设计方法的可行性和有效性。该传感器可满足不同灵敏度需求下对应变的实时监测。     

Novel torsion sensor using a polarization maintaining photonic crystal fiber loop mirror

A novel torsion sensor employing a short length of polarization maintaining photonic crystal fiber was inserted into the fiber loop mirror with an output probe. The sensing scheme was described theoretically by a Jones matrix and experimentally demonstrated. The results showed that the sensitivity of the intensity loss in response to the twist angle may be up to 0.0394 dB/° and a resolution of 0.025° was achieved. This torsion sensor is attractive due to its compact size, insensitivity to temperature, and suitability for longer distance transmission than conventional sensors.