Optically controllable variable fiber optical attenuator integrated in conventional optical fiber

New type of optically controllable variable fiber optical attenuator based on thermo-optical effect in liquid cladding of optical fiber is described. The thermo-optical effect in liquid cladding optical fiber causes refractive index contrast changes in core–cladding interface, what enables to change the propagating optical signal power with temperature. The temperature change is achieved by fiber based heating element using laser radiation. Attenuation up to −12 dB was achieved in static dependence and dynamic response confirmed rise time up to 24 ms.     

Rapid chemical-vapor sensing using optofluidic ring resonators

We develop rapid chemical-vapor sensors based on optofluidic ring resonators (OFRRs). The OFRR is a glass capillary whose circular wall supports the circulating waveguide modes (WGMs). The OFRR inner surface is coated with a vapor-sensitive polymer. The analyte and polymer interaction causes the polymer refractive index to change, which is detected as a WGM spectral shift. Owing to the excellent fluidics, the OFRR exhibits subsecond detection and recovery time with a flow rate of only 1 mL/min, a few orders of magnitude lower than that in the existing optical vapor sensors. The detection limit is estimated to be 5.6 x 10(-6) refractive index units, over ten times better than other ring-resonator vapor sensors. Ethanol and hexane vapors are used as a model system, and chemical differentiation is demonstrated with different polymer coatings.     

Polymer-silica hybrid 1 × 2 thermooptic switch with low crosstalk

A new polymer-silica hybrid 1 × 2 thermooptic switch with significantly low crosstalk is demonstrated. The top cladding and the core layers are composed of polymer, while the bottom cladding layer is made of silica. Since polymer and silica have algebraic signs of their thermooptic coefficients that are opposite to each other, the refractive index of the core changes in the opposite direction to that of the bottom cladding as the temperature is increased. Thus, switching operation is initially done through adiabatic mode evolution in the Y-branch, and then a heated waveguide arm in the Y-branch can enter into the optical cut-off region if the temperature is sufficiently high. Using this phenomenon, low crosstalk performance is achieved. The proposed device has a crosstalk of −35 dB, while most integrated-optic switches with a single stage have a relatively high crosstalk in the region of −20 dB. The switching power of the proposed device is about 70 mW.     

Microbend fiber optic detection of continuously varying refractive index of chlorinated water

In this paper we report a simple microbend fiber optic sensor using a plastic fiber, LED and photodetector assembly for sensing minute variation of refractive index of chlorinated water. Chlorinated water has slightly higher refractive index and gradual release of chlorine from bleaching powder treated water causes a temporal decrease in refractive index of the solution. The evaporation of chlorine from water and the change in refractive index is found to follow a first order exponential decay function of time. Introducing microbends in an optical fiber is easier and less complex than etching of fiber cladding for traditional optical fiber sensors.     

Temperature dependence of symmetric and asymmetric structured Au stripe waveguides

The thermal effects on pigtailed 22-nm-thick, 5-μm-wide and 1-cm-long Au stripe long-range surface plasmon polariton (LRSPP) waveguides, embedded in polymer/polymer layers and in polymer/silica layers, are theoretically and experimentally demonstrated. The polymer and silica cladding layers have thermo-optic coefficients of opposite signs. As the temperature varies the Au stripe LRSPP waveguide embedded in the polymer/polymer layers retains its symmetry in the refractive index, but that embedded in the polymer/silica layers becomes asymmetric in the refractive index. The thermal sensitivity in the optical output power of the symmetric structure is smaller than 0.02 dB/°C but the sensitivity of the asymmetric structure is ∼ 0.3 dB/°C. These structures open up potential applications of the LRSPP waveguides for temperature independent/dependent photonic devices.     

Numerical ray tracing through a modified cladding fiber optic segment sensors

By using 3-D geometric optics, the effect of a modified cladding on the transmission of light through optical fiber is investigated. Analysis of the light transmission of the optical fiber as function of the modified cladding refraction index and length are presented for various input illumination focused and compared with 3-D ray theory. Applications to chemical sensors are also discussed.The intensity of light signal transmitted through an optical fiber, which its cladding over a finite length is removed, is used as a sensor of refractive of liquids, in which the fiber is immersed. The transmitted light intensity is measured as a function of liquid refractive index for different lengths of the unclad section of the fiber and at each unclad length its sensitivity to change in refractive index of liquid is presented.     

光纤型热光可调光衰减器的设计及其衰减分析

提出了一种基于热光调节的可调光衰减器结构。该衰减器通过腐蚀光纤包层到一定厚度和长度后,在表面涂覆较大热光系数的聚合物材料得到。从模场变化角度分析了传输光束的衰减与涂覆材料折射率的关系,并从实验上测试了使用不同涂覆材料时的衰减。理论分析与实验结果均表明在涂覆材料折射率略大于原光纤包层材料折射率时,涂覆材料折射率微小的变化将引起传播光束衰减的大幅度变化,并且光纤被腐蚀的长度越长或包层材料剩余厚度越小,衰减越大。因此,由热光系数大、折射率略大于光纤包层的聚合物材料所组成的可调光纤衰减器,具有衰减调节范围大且功耗小、插入损耗小、成本低、低偏振特性、易于与其它光纤器件耦合或集成等特点。     

Investigation on characteristics of W-type fiber with an inner cladding made of negative refractive index materials

A doubly clad optical fiber with an inner cladding made of negative refractive index material was proposed and the modes distribution, dispersion and time delay were investigated by fully vectorial numerical method. The results indicate that HE₁₂ mode can be operated as a single mode, the cut-off frequency of modes shifts to low normalized frequency with increasing thickness of inner cladding made of negative index materials, large negative dispersion and time delay can be obtained and tailored by the inner cladding. These results provide theoretical basis for designing novel fibers or optical devices.     

Automatic fringe analysis of the induced anisotropy of bent optical fibres

A new theoretical model considering the refraction of the incident light beam by the fibre is suggested to determine the refractive index profile of bent optical fibres. This new model (slabs model) considering the cross section of the bent optical fibre consists of large number of slabs. The slabs model bases on the refraction of the incident beam by the fibre. The refractive index profile of the optical fibre cladding before bending obtained using the automated Fizeau interferometer with the aid of suggested model is compared with other models such as, the homogenous model and the multilayer model to verify the ability of this slab model. The refractive index profile of the bent optical fibre cladding is investigated using this suggested model. In addition, the new model is used to obtain the induced birefringence and the guiding parameters. The bending radius is recommended to be greater than 7.1 mm for the used optical fibre. The consideration of the refraction increases the accuracy of the results.     

基于无芯光纤的多参数测量传感器

设计并制作了一种基于单模-无芯-单模-无芯-单模光纤结构的马赫-曾德尔传感器,可用来同时测量折射率和温度.该传感器中,两处无芯光纤充当输入、输出耦合器,中间单模光纤作为传感臂.利用有限元仿真和理论分析,确定耦合器和传感臂的最优长度为15 mm.在无芯光纤中激发出的高阶模进入单模光纤的包层传输,由于倏逝场的作用,受到环境折射率和温度的影响.选取透射谱不同干涉级次的波谷作为研究对象,实现了折射率和温度的同步测量.实验结果表明:1545 nm附近干涉谷的折射率和温度灵敏度分别为–153.89 nm/RIU(refractive index unit)和0.166 nm/℃;1570 nm附近干涉谷的折射率和温度灵敏度分别为–202.74 nm/RIU和0.183 nm/℃.该传感器在实现折射率和温度同步测量的同时,仍能保持较高灵敏度,在生物医疗等方面有着较好的应用前景.     

Relative humidity sensor based on SMS fiber structure with polyvinyl alcohol coating

A novel relative humidity (RH) sensor based on single-mode–multimode–single-mode (SMS) fiber structure is presented. The sensors are created through coating a thin layer of polyvinyl alcohol (PVA) on the multimode fiber deleted the cladding trough HF solution cauterization as the sensitive cladding film, whose refractive index varies as a function of humidity level. Due to the SMS fiber structure's sensitivity to ambient refractive index, the transmission spectra of SMS fiber structure coated PVA film are modified under exposure to different ambient humidity levels ranging from 30% to 80% RH. The related numerical simulations of transmission spectra of SMS fiber structure with different surrounding refractive index are also proposed. The sensitive of the RH measurement of 0.09 nm/% RH in the range from 30% to 80% RH is experimentally achieved. Meanwhile the intensity of wavelength at 1543 nm is decreasing as the humidity increasing. The experimental results obtained are consistent with the conclusion obtained by numerical simulating.     

Optical sensors based on Fabry–Perot resonator and fringes of equal thickness structure

We propose theoretically two optical sensor structures based on Fabry–Perot resonator and fringes of equal thickness structure. Different from the conventional slab waveguide sensors in which the sample interacts with the evanescent field in the cladding layer, the proposed sensors contain the sample in the core layer. The first proposed sensor comprises a piezoelectric material as a substrate with the driving potential difference as the sensing probe for refractive index changes of the sample. The second sensor comprises fringes of equal thickness structure with the number of fringes per unit length is the probe for changes in the index of the sample. The calculations reveal that the proposed sensors have high sensitivity to changes in the refractive index of the sample.     

Synthesis of photosensitive poly(methyl methacrylate-co-glycidyl methacrylate) for optical waveguide devices

Photosensitive poly(MMA-co-GMA) for optical waveguide was synthesized, and the refractive index of the polymer film was tuned in the range of 1.481–1.588 at 1550 nm by mixing with bis-phenol-A epoxy resin. The film, which was made by spinning coated the poly(MMA-co-GMA) with photo initiator, had good UV light lithograph sensitivity, high glass transition temperature (T _g : 153°C, after crosslinking) and good thermal stabilities (T _d : up to 324°C, after crosslinking). The optical waveguides with very smooth top surface were fabricated from the resulting polymer by direct UV exposure and chemical development. For waveguides with cladding, the propagation losses of the channel waveguides were measured to be below 3 dB/cm at 1550 nm.     

Refractive index sensor based on high-order surface plasmon resonance in gold nanofilm coated photonic crystal fiber

We propose a novel kind of wide-range refractive index optical sensor based on photonic crystal fiber(PCF) covered with nano-ring gold film.The refractive index sensing performance of the PCF sensor is analyzed and simulated by the finite element method(FEM).The refractive index liquid is infiltrated into the cladding air hole of the PCF.By comparing the sensing performance of two kinds of photonic crystal fiber structures, a wide range and high sensitivity structure is optimized.The surface plasmon resonance(SPR) excitation material is chose as gold, and large gold nanorings are embedded around the first cladding air hole of the PCF.The higher order surface plasmon modes are generated in this designed optical fiber structure.The resonance coupling between the fundamental mode and the 5 th order surface plasmon polariton(SPP)modes is excited when the phase matching condition is matched.Therefore, the 3 rd loss peaks appear obvious red-shift with the increase of the analyte refractive index, which shows a remarkable polynomial fitting law.The fitnesses of two structures are 0.99 and 0.98, respectively.When the range of refractive indices is from 1.40 to 1.43, the two kinds of sensors have high linear sensitivities of 1604 nm/RIU and 3978 nm/RIU, respectively.     

Polarization maintaining fibers for application in magnetic field measurements

Optical fibers may be applied in measurements of electrical current, particularly as so-called optical current transformers. Electric current sensors, in which optical fibers are used are small, light, cheap and safe. Their sensitivity is, however, due to the restricted magnetootpic properties of optical fibers, rather small. Moreover, these sensors are susceptible to deformations of the optical fiber. An increase of their sensitivity consists in lengthening the distance of optical fiber on which the magnetic field acts. However, this can lead to an increase of disturbances caused by changes of internal stresses. The negative effects can be reduced by applying optical fibers with a higher magnetooptic sensitivity and a lower susceptibility to mechanical stresses and deformations. The present paper deals with side-hole optical fibers with a decreased birefringence reducing the susceptibility to deformations. The optical fibers consist of a multicomponent glass with a higher value of the refractive index, thanks to which the sensitivity to the effect of the external magnetic field is increased. In future such optical fibers are planed to be applied in magnetooptic sensors.     

非线性包层光纤中TE0模的传播特性分析

本文对具有Kerr非线性包层和线性匀芯的光纤在不同光功率下的传播特性进行了理论分析和数值计算.结果表明,在适当光功率下,当模折射率N等于芯折射率n_f时,芯场变得相当均匀,而包层场迅速衰减.对于自聚焦包层,当从N<n_f逐渐变到N>n_f时,芯场剖面越过N=n_f从凸变凹.在拐点,芯场成为均匀的.论文给出了模场分布和光功率与模折射率的关系.指出纤芯出现匀场预期会在光纤器件、光电子器件、光子器件中得到应用.     

光纤纤芯及包层模有效折射率计算及仿真

光纤结构设计、模间色散求解、光纤光栅模式耦合等问题的研究, 都需要对光纤纤芯及包层模的有效折射率进行精确计算. 本文以光纤三层结构模型为基础, 结合该模型下的模式本征方程, 使用截弦法求解了纤芯模有效折射率, 并将计算结果与COMSOL软件模拟的对应纤芯模的传输光场进行对比, 验证了计算结果正确.使用区间遍历算法对包层模有效折射率进行了求解, 与已有的传统方法相比, 该方法可以有效防止求解过程中根的遗漏、避免特征方程产生的奇点, 并能保证模式的正规性.本文采用Mathematica软件对求解过程进行仿真, 获得了纤芯模和包层模有效折射率与波长关系曲线. 关键词： 光纤传输模式 有效折射率 截弦法 区间遍历算法     

Fabrication and Gamma-Ray Irradiation Effect on Optical and Mechanical Properties of Germano-Silicate Glass Fibers with Inner Cladding of B and F Doped Silica Glasses

ABSTRACT

The effect of glass composition, pure silica glass, boron-doped and fluorine-doped silica glasses of inner cladding, in the germano-silicate glass core fibers on optical and mechanical properties upon the γ-ray irradiation was investigated. Enhanced radiation hardening at 1,550 nm was found in both the B- and F-doped fibers after the γ-ray irradiation with dose-rate of 1.25 kGy/h. The radiation-induced attenuation (RIA) was found to increase in the order of the B-doped fiber, the F-doped fiber, and the silica fiber. While no major influence on the refractive index of the fibers after the γ-ray irradiation was found, the residual stress was slightly changed.     

侧边抛磨光纤波导传输特性的理论分析

在建立侧边抛磨光纤D型光纤边界条件的基础上,用三维有限差分光束传输法计算和分析了侧边抛磨光纤器件的光功率衰减随光纤的侧边抛磨长度、光纤侧边抛磨后剩余包层的厚度、以及填充聚合物材料折射率三个参量变化的特性.结果表明,侧边抛磨光纤器件的光功率衰减随着抛磨长度的增加而增大;当抛磨长度等于9 mm时,光功率衰减随着剩余包层厚度的增大而单调递减.而当抛磨长度大于9 mm时,剩余包层厚度小于3 μm的范围内,光衰减随着剩余包层厚度的增加出现振荡;当聚合物折射率与纤芯折射率相同时,光功率衰减最大.     

Effect of annealing temperature on the optical constants of zinc oxide films

In this paper, the effect of annealing temperature on optical constants was studied. The ZnO films were deposited on microscopic glass substrates using the sol-gel method for various annealing temperatures. The deposited zinc oxide (ZnO) films were characterized by an X-ray diffractometer (XRD), a spectrophotometer and scanning electron microscopy (SEM). The transmittance spectra recorded through the spectrophotometer exhibits 90% transmittance. The XRD spectra showed polycrystalline nature of ZnO film. Optical constants were determined through transmittance spectra using an envelope method. It was found that there was a significant effect of annealing temperature on the refractive index and extinction coefficient of deposited ZnO films. In this experiment, the optimum refractive index value of 1.97 was obtained at 350 °C annealing temperature at visible (vis) wavelength. The optical energy gap was found to be of ∼3.2 eV for all the samples. The top view of SEM showed the ZnO grain growth on the glass substrates.