Temperature dependence of the refractive index of optical fibers

Many experimental investigations on the temperature dependence of the refractive index of optical fibers have been reported previously, however a satisfying theoretical explanation for it is still absent. In this paper, a theoretical model about the temperature dependence of the refractive index of optical fibers is presented and it is in agreement with the previous experimental results. This work is a significant reference for the research and development of temperature sensors based on optical fiber delay lines.

Cascaded tilted fiber Bragg grating for enhanced refractive index sensing

We proposed and experimentally demonstrated a cascaded tilted fiber Bragg grating（TFBG） for enhanced refractive index sensing. The TFBG is UV-inscribed in series in ordinary single-mode fiber（SMF） and reduced-diameter SMF with the same tilt angle, and then excites two sets of superposed spectral combs of cladding modes. The cascaded TFBG with total length of 18 mm has a much wider wavelength range over 100 nm and narrower wavelength separation than that of a TFBG only in the SMF, enabling an enlarged range and a higher accuracy of refractive index measurement. The fabricated TFBG with the merits of enhanced sensing capability and temperature self-calibration presents great potentials in the biochemical sensing applications.

Random Raman Fiber Laser as a Liquid Refractive Index Sensor

In this paper,a new concept of forward-pumped random Raman fiber laser(RRFL)-based liquid refractive index sensing is proposed for the first time.For liquid refractive index sensing,the flat fiber end immersed in the liquid can act as the point reflector for generating random fiber lasing and also as the sensing head.Due to the high sensitivity of the output power of the RRFL to the reflectivity provided by the point reflector in the ultralow reflectivity regime,the proposed RRFL is capable of achieving liquid refractive index sensing by measuring the random lasing output power.We theoretically investigate the effects of the operating pump power and fiber length on the refractive index sensitivity for the proposed RRFL.As a proof-of-concept demonstration,we experimentally realize high-sensitivity half-open short-cavity RRFL-based liquid refractive index sensing with the maximum sensitivity and the sensing resolution of-39.88W/RIU and 2.5075×10^(-5) RIU,respectively.We also experimentally verify that the refractive index sensitivity can be enhanced with the shorter fiber length of the RRFL.This work extends the application of the random fiber laser as a new platform for highly-sensitive refractive index sensing in chemical,biomedical,and environmental monitoring applications,etc.

Long Period Grating Imprinted on a Flat-Shaped Plastic Optical Fiber for Refractive Index Sensing

A corrugated surface long period grating(LPG)was fabricated on a flat-shaped plastic optical fiber(POF)as a refractive index(RI)sensor by a simple pressing with the heat pressure and mechanical die press print method.The light propagation characteristics of an LPG imprinted on a multi-mode POF were analyzed by the method of geometrical optics.Theoretical and experimental results showed that the structural parameters of the sensor affected the RI sensing performance,and the sensor with a thinner flat thickness,a deeper groove depth of the corrugated surface LPG,and a longer LPG exhibited better RI sensing performance.When the POF with a diameter of 1 mm was pressed with the heat pressure to a flat shape with a thickness of 600μm,an LPG with a period of 300μm,a groove depth of 200μm,and a length of 6 cm was fabricated on it,and the RI sensitivity of 1447%/RIU was obtained with a resolution of 5.494×10^(−6) RIU.In addition,the influences of the POF cladding,tilting of LPG,and bending of the sensing structure were investigated.The results demonstrated that after removing the cladding and tilting or bending the LPG,the RI sensing performance was improved.When the LPG imprinted on the flat-shaped POF was bent with a curvature radius of 6/πcm,the highest sensitivity of 6563%/RIU was achieved with a resolution of 2.487×10^(−9) RIU in the RI range of 1.3330–1.4230.The proposed sensor is a low-cost solution for RI measurement with the features of easy fabrication,high sensitivity,and intensity modulation at the visible wavelengths.

Refractive index and temperature sensing characteristics of an optical fiber sensor based on a tapered single mode fiber/polarization maintaining fiber

An evanescent field optical fiber sensor based on a short section of polarization maintaining fiber spliced with a tapered single mode fiber is proposed and experimentally investigated. We mainly focus on the refractive index （RI） and temperature sensing characteristics of this compact device. The transmission spectrum of the resonance wavelength, induced by the interference between the excited low order cladding modes and core modes, shows the quadratic function relationships with RI and linear relationships with temperature. Thus, the proposal of this simple-to-fabricate, compact, and low cost sensor shows its possible potential in the sensitive detection field.

Intensity modulated silver coated glass optical fiber refractive index sensor

Miniature optical fiber sensors with thin films as sensitive elements could open new fields for optical fiber sensor applications. Thin films work as sensitive elements and a transducer to get response and feedback from environments, in which optical fibers act as a signal carrier. A novel Ag coated intensity modulated optical fiber sensor based on refractive index changes using IR and UV-Vis （UV-visible） light sources is proposed. The sensor with an IR light source has higher sensitivity compared to a UV-Vis source. When the refractive index is en- hanced to 1.38, the normalized intensity of IR and UV-Vis light diminishes to 0.2 and 0.8. respectively.

基于球形长周期光纤光栅的宽动态范围位移传感器实验研究

[目的]针对光纤位移传感器动态范围窄的问题,设计一种结构简单、易于制备的气球形长周期光纤光栅(LPFG)位移传感器。[方法]采用RSOFT软件进行仿真与优化,得到光纤在不同曲率下的光谱形态,以此来确定测量区间。通过将多模光纤周期性嵌入单模光纤形成的气球形长周期光纤光栅(MMF-BLPFG),提供用于测量位移的参考峰。使用精密的连续切割装置作为实验基础,制备与仿真结果一致的实验样品进行测试。[结果]通过测量2个谐振峰的漂移,实现了36 mm的最大位移测量范围。[结论]该研究成果在舰船水下疏水空间管系的稳定性测量和连续监测等需要大规模测量的场景中具有良好的应用潜力。

基于表面等离子体共振技术的光子晶体光纤传感器研究

为了实现对待测介质折射率的高灵敏度检测,设计并研究了一种基于表面等离子体共振技术的光子晶体光纤折射率传感器。该传感器的内外空气孔呈正六边形排列,在包层外壁上涂覆银-石墨烯纳米薄膜,通过纤芯基模和表面等离子体模的耦合程度来检测周围环境的折射率变化。研究表明,该传感器可以实现折射率在1.37~1.38范围内的检测,最高灵敏度可达40000nm/RIU,分辨率可达4.17×10-5RIU。

Side-polished SMS based RI sensor employing macro-bending perfluorinated POF

A refractive index(RI)sensor based on perfluorinated plastic optical fiber(PF-POF)is introduced in this paper.The PF-POF as multi-mode fiber was side-polished(SP)to form a macro-bending single-mode-multimode-single-mode(SMS)structure.Both ends of the sensor were closely connected to single-mode quartz optical fiber(SMF).The spectral char-acteristics of the sensor are measured,analyzed and discussed.The results show that when the length of PF-POF is 8 cm,the macro-bending radius is 3 cm,and the SP-depth is 20μm.The intensity sensitivity reaches−219.504 dBm/RIU in the range of RI=1.330~1.356.A reference is provided for the application of PF-POF in RI sensor in the future.The sensor is featured with low-cost,good flexibility and high efficiency.

A Novel High Sensitivity Refractive Index Sensor Based on Multi-Core Micro/Nano Fiber

A refractive index sensor based on a multi-core micro/nano fiber is proposed for low refractive index solutions. At first, the mode field distribution of the tapered multi-core fiber is analyzed with the finite element model (FEM). After that, the relationship between the refractive index sensitivity and the diameter of the multi-core micro/nano fiber is calculated. At last, four sensors with different sizes are explored, and when the taper length is 16.20 mm, the refractive index sensitivity of the sensor can reach 5815.50nm/RIU, which agrees with the theoretical analysis. The refractive index measurement error is less than 0.5 %o, which has a high practical application value. The longer the taper length is, the smaller the fiber diameter is. According to the theoretical analysis, when the fiber diameter is less than 4.864 gm, the structure sensor\ refractive index sensitivity is higher than 10000 nm/RIU. At the same time, when the sensor's taper length is 15.99 mm, its temperature sensitivity is -0.1084nm/°C. Compared with single-mode fiber, the sensor proposed here has the advantages of stability, compact structure, and high sensitivity, which has a potential in the field of seawater salinity measurement.

螺旋形塑料光纤表面等离子体共振折射率传感器

研究了基于波长调制的螺旋形塑料光纤(plastic optical fiber, POF)表面等离子体共振(surface plasmon resonance, SPR)折射率传感器。采用机械热压和扭曲法将塑料光纤制备成螺旋形,在螺旋形POF上通过磁控溅射蒸镀一定厚度(约50 nm)的金属薄膜来激励SPR效应,从而形成螺旋形POF-SPR传感器。通过对螺旋形POF-SPR传感器的结构进行修饰,研究不同结构参数对折射率传感特性的影响。实验结果表明:由厚度为500μm扁平形POF扭制、螺纹数为4的螺旋形POF-SPR传感器具有较好的线性度和折射率传感特性,在折射率为1.335~1.400范围内测得的灵敏度为1 262 nm/RIU。该传感器具有成本较低、制备简单、结构稳定等优点。

基于模间干涉的反射型全光纤液体折射率传感器

基于模间干涉原理设计并实验制作了一种反射型全光纤液体折射率传感器,该传感器是由一段无芯光纤熔接在两个单模光纤之间制作而成。其工作原理是由单模光纤和无芯光纤耦合点处激发出高阶模式,经过末端单模光纤端面的反射,在无芯光纤和单模光纤界面发生二次耦合,从而形成模间干涉。数据处理后可得,在氯化钠、甘油和蔗糖溶液中传感器有不同的折射率灵敏度,每种溶液分别为-104.14345dB/RIU、-153.91078dB/RIU和-95.40521dB/RIU。温度灵敏度为35.27pm/℃,温度在强度上的改变对折射率的测量影响非常小,相对于该波峰波长漂移量可以忽略不计,温度的串扰较小。所提出的传感器具有结构简单、机械性能优良和灵敏度高等优点,在液体折射率的监测领域具有一定的应用潜力。

基于强度调制的光纤激光折射率传感器

提出了一种基于光纤布喇格光栅与多模凹锥光纤级联结构的低探测极限光纤激光折射率传感器。采用光纤环形激光器内腔调制技术,获得了稳定、高边模抑制比和窄半峰全宽的激光信号,量化研究了有源结构下凹锥直径与液体折射率变化间响应关系。当凹锥直径为30.53μm时,最大折射率灵敏度可达-128.636 dB/RIU。考虑3σ噪声条件,实际探测极限可达8.49×10-4RIU。该传感器具有输出稳定和低温度串扰的优点,在生化传感和环境监测等方面具有潜在的应用前景。

Novel optical fiber current sensor based on magnetic fluid

A novel fiber optic Fabry-Perot（F-P） current sensor is developed based on magnetic fluid as the medium in F-P interference cavity.A signal demodulation method based on slanted fiber Bragg grating（FBG） wavelength measurement system is proposed.Theory and principle of electromagnetic-controlled refractive index of the magnetic fluid is described,as well as the structure of the sensor system.Preliminary experiments are carried out,and the results indicate that there is a fairly good linearity of the measurement characteristic.The thickness of magnetic fluid film and initial concentration will affect the measurement results.

Advances in Optical Fiber Bragg Grating Sensor Technologies

作者在光纤维布拉格的发展考察他们的最近的进展栅栏(FBG ) 传感器技术。在纤维栅栏传感器的简短评论以后，几个最新发达的 FBG 传感器被描述。与纤维材料，微观结构和 processing 以后技术的连续发展， FBG 传感器三十年以前在永久栅栏的第一示范以后仍然是有创造性的。

Modeling of Refractive Index Sensing Using Au Aperture Arrays on a Bragg Fiber Facet

A finite-difference-time-domain(FDTD)approach is undertaken to investigate the extraordinary optical transmission(EOT)phenomenon of Au circular aperture arrays deposited on a Bragg fiber facet for refractive index(RI)sensing.Investigation shows that the choice of effective indices and modal loss of the Bragg fiber core modes will affect the sensitivity enhancement by using a mode analysis approach.The critical parameters of Bragg fiber including the middle dielectric RI,as well as its gap between dielectric layers,which affect the EOT and RI sensitivity for the sensor,are discussed and optimized.It is demonstrated that a better sensitivity of 156±5 nm per refractive index unit(RIU)and an averaged figure of merit exceeding 3.5 RIU‒1 are achieved when RI is 1.5 and gap is 0.02μm in this structure.

基于拉锥细芯光纤的双参量同时测量传感器

该文研制了一种基于拉锥细芯光纤、可同时测量折射率与应变的传感器。传感器结构为“单模光纤-多模光纤-锥形细芯光纤-多模光纤-单模光纤”,由于细芯光纤中部腰锥尺寸变小,构成马赫-曾德尔干涉仪。实验结果表明,传感器透射谱线谐振峰或谐振谷的中心波长与环境折射率和轴向应变之间均有良好的线性关系,折射率灵敏度最高可达-38.677 nm/RIU,轴向应变灵敏度最高为-4.4 pm/με,取两个谐振峰或谐振谷构建矩阵,消除两物理量之间的交叉敏感,能够实现双参量同时测量。该传感器制作简单,成本低,鲁棒性优良,在折射率与轴向应变传感领域有一定的应用价值。

Performance Evaluation of a Bilayer SPR-Based Fiber Optic RI Sensor With TiO2 Using FDTD Solutions

我们建议了新 bilayer 表面电浆子有银和 TiO 的 over-layer 的基于回声的光纤的折射索引传感器 < 潜水艇 class= “ a-plus-plus ” > 2 。我们数字地调查了 TiO 的最佳的厚度 < 潜水艇 class= “ a-plus-plus ” > 在建议传感器中的 2 over-layer 并且用有限差别的时间在水的媒介基于 silver-and-gold 的典型的二金属的层把它的性能比作那域途径。我们证明 TiO 的使用 < 潜水艇 class= “ a-plus-plus ” > 2 over-layer 极大地作为 over-layer 与黄金与那相比以敏感和 signal-to-noise 比率改进传感器表演。不仅做 TiO < 候补选手 class= “ a-plus-plus ” > 2 over-layer 提议为克服氧化的黄金的一种划算的选择问题，而且它允许回声 wavelength-tunability。

Optical fiber hydrogen sensor based on light reflection and a palladium-sliver thin film

Thin alloy films of palladium(Pd) and silver(Ag) are deposited onto glass substrates via the direct current(DC) magnetron technique.The hydrogen sensor probe consists of optical fiber bundle and Pd/Ag optical thin film.when the sensor is exposed to hydrogen,the refractive index of Pd/Ag optical thin layer will diminish and cause attenuation changes of the reflective light.It is observed that the thickness of Pd/Ag alloy layer can affect the hydrogen sensor signal.Under different substrate temperatures,several Pd/Ag samples are coated with different thicknesses of Pd/Ag alloy,and the results of a hydrogen sensor based on reflective light from the Pd/Ag alloy thin film are discussed.