基于细芯光纤与双球结构的干涉型光纤传感器

制作了一种基于细芯光纤TCF(Thin-Core Fiber)和双球结构的干涉型光纤传感器.在两根单模光纤的一端分别制作球形结构,两个球形结构由细芯光纤相连构成MZ干涉结构,实现了对温度、折射率、拉力3个物理量的测量.实验结果表明,温度、折射率、拉力的灵敏度分别是0.066 5 nm/℃、-33.652 nm/RIU、-0.360 8 nm/N,且线性度良好.该传感结构在环境监测、医疗卫生和安全监测等领域有着广泛的应用.     

High-sensitive SPR sensing with Indium Nitride as a dielectric overlay of optical fibers

In this work, an Indium Nitride (InN) dielectric overlay has been used to develop a surface plasmon resonance optical fiber sensor. Although InN is a very promising material in electronics industry, this is the first time that this kind of material is used for optical sensing. The obtained results show an improvement of the reliability and long term stability with respect to previous devices made with the same technology. More remarkably, the sensitivity increases up to 11,800 nm/RIU in the range of outer refractive indices between 1.415 and 1.429, the highest sensitivity achieved with this kind of devices. Therefore, a novel application of the InN to optical fiber sensors is demonstrated. The use of this material would be of great interest to produce new SPR-based devices for chemical and biological sensing.     

Optical fiber-based evanescent ammonia sensor

An optical fiber-based evanescent gaseous ammonia sensor is designed and developed. The sensing dye, bromocresol purple (BCP), is immobilized in the substitutional cladding using sol–gel process. The sensing properties of the optical fiber sensor to gaseous ammonia at room temperature are presented. This newly developed ammonia sensor exhibits good reversibility and repeatability. The effect of different carrier gases, argon, nitrogen, and air on sensing properties of the ammonia sensor is investigated. The sensor with air as carrier gas has the best response time and sensitivity. In order to improve the response time of the optical fiber evanescent ammonia sensor, an elevated ambient temperature is applied and thoroughly investigated. A fast response time of 10 s was obtained at 55.5 °C with the carrier gas of air or argon. These experimental results have demonstrated that a fast response optical fiber evanescent gaseous ammonia sensor can be constructed by applying slightly elevated ambient temperature.     

Single-mode—multimode—single-mode and lossy mode resonance-based devices: a comparative study for sensing applications

In this work, a thin-film consisting of 15 bilayers (estimated thickness: 210 nm) of titanium (IV) oxide and poly(sodium 4-styrenesulfonate) is simultaneously deposited onto two optical fiber structures: a single-mode—multimode—single-mode (SMS) device and a lossy mode resonance (LMR)-based device. The performance of both structures, as refractometers and relative humidity sensors, is studied and compared. In both cases, the sensitivity of the LMR-based device (955 nm/RIU and 3.54 nm/RH %, respectively) highly improves the one of the SMS (142 nm/RIU and 0.3 nm/RH %). These facts can be taken into account when developing sensors based on either SMS or LMR technologies.     

采用拍频检测的内嵌型微环传感器研究

提出了一种内嵌型微环传感结构。利用内嵌型结构产生的高Q值滤波峰,采用拍频检测技术,可以实现高灵敏度传感器。采用传输矩阵法分析了内嵌微环半径对滤波峰位置及相邻滤波峰之间关系的影响。内嵌微环的滤波峰产生了分裂,其波长间距很小,且随折射率变化波长间距也会变化。利用该器件构建了拍频检测系统,并对该器件进行传感分析。仿真结果表明,该结构的传感灵敏度为1×10-4折射率单位(RIU),其频率偏移为4 MHz/1×10-4RIU。     

Absorption-based fiber optic surface plasmon resonance sensor: a theoretical evaluation

In this paper, an optical absorption based fiber optic surface plasmon resonance (SPR) sensor has been studied theoretically. The theoretical treatment is based on Kretschmann’s SPR theory and the Lorentz model that expresses a damped harmonic oscillator is included in the treatment for optical absorption in the sensing layer. The optical source considered is an un-polarized collimated beam. The light is coupled to the fiber using a microscope objective that focuses the beam at the center of the input face of the fiber. The effects of the parameters related to the sensing region, the light source and the optical fiber on the sensitivity and the operating range of the SPR sensor have been studied with the help of numerical calculations and computer simulations. It has been found that the excitation frequency in absorption-based fiber optic SPR sensor is an important parameter. The sensitivity is better for the lower off-resonance excitation frequency. The sensitivity and the operating range of the sensor are better for large value of the core diameter. The optimization of numerical aperture of the fiber, film thickness and the length of the sensing region is required to achieve the maximum sensitivity. Further, the increase in the extinction coefficient of the sample increases the sensitivity of the sensor while the decrease in the width of its absorption spectrum increases the sensitivity. The sensitivity and the operating range of the sensor are better for small values of the refractive index of the absorbing sample.     

Sol–gel derived polycrystalline Cr1.8Ti0.2O3 thick films for alcohols sensing application

The powder sample of Cr_1.8Ti_0.2O₃ (CTO) was obtained by a sol–gel method. The thick films were developed on identical ceramic tubes of 4 mm length comprising of two Au-electrodes and printing an eight-layer film prepared by mixing CTO with glass powder and -terpinol as an organic vehicle. X-ray powder diffraction (XRD) patterns showed the formation of a single phase. The scanning electron microscope (SEM) images of the ceramic sensor treated at 850 °C revealed that the grain size was larger than 400 nm for the individual isolated grains on the surface, and the agglomerated dense spheroidal platelets had the size of 1–4 μm in diameter. The AC impedance measurement in ambient air showed that the resistance decreased nearly by two orders of magnitude with an increase in temperature in the range of 400–600 °C for both the powder sample and the thick film, and the activation energy E_a derived from the measurement was found to be 0.35 and 0.36 eV for the powder and the film, respectively. The films were exposed to various concentrations of alcohols (0.4–1.2 ppm of methanol and 1.0–5.0 ppm of ethanol), followed by determination of sensor response, sensitivity and reversibility and reproducibility. The origin of the gas response was attributed to the surface reaction of R-OH (R = methyl and ethyl group) with O⁻_(ads) to form adsorbed R-CHO, which was desorbed as a gas at 400 °C after the sensor departing from the gas.     

UV-LIGA interferometer biosensor based on the SU-8 optical waveguide

SU-8 resist was used as a core/cladding waveguide material to fabricate a Mach–Zehnder interferometer (MZI) for biochemical sensing. The refractive index of the SU-8 resist was fine-tuned with a Δn of 0.004 for single-mode transmission. The UV lithography processes of the SU-8 resist were also optimized to pattern the high resolution (1 μm) and high aspect ratio (A_R = 6) Y-branch structure of the optical interferometer. Optical measurements reveal that the SU-8 MZI chip can efficiently transmit the NIR laser (λ = 1310 nm) with a total loss less than 6 dB. When one branch of the MZI is in contact with the analyte, the interfered intensity stabilizes after the soaking time exceeds 5 min. NaCl solution with a concentration of 10⁻⁹ g/l can be detected using the SU-8 MZI chip. In the future, the polymer MZI chip can be mass-produced by molding process (or the LIGA process). The low-cost, label-free, real-time and high-sensitivity MZI chip will benefit many applications related to biological, environmental and industrial detection.     

A multichannel surface plasmon resonance sensor using a new spectral readout system without moving optics

Surface plasmon resonance (SPR) sensors with spectral interrogation provide a high refractive index resolution, a large dynamic range and a fixed optical detection module. In this work, we propose a new multichannel spectral detection unit that uses only one spectrometer to measure the reflection spectrum from multiple sensing spots serially without any mechanical movement. This spectral detection unit is designed based on a spatial light modulator (SLM) configured as a programmable optical aperture for the spectrometer. To demonstrate this concept, a five-channel laboratory SPR prototype was built based on the proposed multichannel detection unit, and we evaluated the device's sensitivity and resolution using a refractive index test. Refractive index resolution of 1.4 × 10⁻⁶ refractive index units (RIU) can be reached using the five-channel prototype. This sensor is suitable for low-cost multichannel biosensing applications that do not contain fast kinetics.     

Cholesteric liquid crystals for detection of organic vapours

Studies on the use of cholesteric liquid crystals (CLCs) as sensing phase for detection of organic vapours in air are described. Stock solutions of 1.0% (w/v) cholesteryl nonanoate (CN) and cholesteryl chloride (CC) were prepared in tetrahydrofuran. Binary mixtures, with compositions ranging from 0.18 to 0.25% of CC and 0.82–0.75% of CN, respectively, were prepared by appropriate mixing of the stock solutions. Films were cast by pipetting three 10 μl aliquots of the CLC solution mixture onto a glass disk, whose reverse side was made black to absorb unscattered light. The glass disk was adapted to the common end of a bifurcated optical fibre bundle and placed in a glass vial, which provided a headspace of organic vapours. Measurements were carried out at 27±1 °C, a temperature in which the CLC mixtures maintain their liquid crystalline properties. The responses of the CLC mixtures to vapours of ethanol, acetone, benzene, pyridine and hexane were investigated. The colour of the sensing phases depended on their compositions and exposure to organic vapours gives rise to a change in the optical characteristics of liquid crystals. It was found that the CLC layers containing 0.23–0.25% of CC had no significant change in optical properties when exposed to organic vapours and that ethanol did not cause any optical changes in the liquid crystal layers. Benzene as well as hexane always turned all the coloured liquid crystalline layers to colourless. The CLC layers exhibited different behaviours to vapours of acetone and pyridine. For example, the wavelengths of maximum scattering for the 0.19% CC layer were 530 nm in air, 545 nm in pyridine and 580 nm in acetone. The CLC layers showed reversibility. The lifetimes of these layers (interval of time in which the liquid crystalline phase exists, before crystallisation) were investigated by employing acetone and n-hexane vapours. Average lifetimes of 14–15 min were found for films in contact with these vapours, while a lifetime of 205 min was possible when the CLC film was exposed to air.     

基于保偏光纤马赫曾德干涉结合布拉格光纤光栅的折射率传感器

为了能同时测量折射率和温度,提出了一种基于保偏光纤马赫曾德干涉仪结合布拉格光纤光栅的折射率传感器。保偏光纤在两个单模光纤之间通过错位熔接形成马赫曾德干涉仪,布拉格光纤光栅连接在马赫曾德干涉仪的输出端用作温度补偿。实验结果表明保偏光纤快轴和慢轴两个正交模式的干涉谱随着折射率的变化而变化,当折射率范围在1.3426到1.3692时,快轴和慢轴方向上的灵敏度分别为-118.38 nm/RIU和-80.02 nm/RIU。当折射率在1.3692到1.4191时,快轴和慢轴方向上的灵敏度分别为48.3 nm/RIU和25.75 nm/RIU。同时通过测量布拉格光纤光栅谐振波长的偏移量,折射率和温度能被同时测量。     

基于双D光纤传感器的陶瓷泥浆浓度仪的设计

为了克服陶瓷泥浆浓度落后的检测技术和低效率,研制了一种新型的检测仪器.依据Mie散射理论,在入射波长、入射光强、探测距离、粒径尺寸参量、折射率,后向散射角已知时,后向散射光强就与粒子数浓度成正比.在实验中,把光信号通过双D型光纤传感器中的一支光纤射入陶瓷泥浆,另一支光纤接收陶瓷泥浆颗粒对光信号的后向散射光线.分别检测浓度为40%-60%的陶瓷泥浆样本,记录、分析这组电压值和陶瓷泥浆浓度的关系后知道:在陶土含量为40%-60%之间的数据曲线是线性的.利用这一个结果,研制了陶瓷泥浆浓度检测仪,并详细说明陶瓷泥浆浓度检测仪的结构及特点.     

Surface plasmon resonance in chalcogenide glass-based optical system

The surface plasmon resonance phenomenon has been studied in a chalcogenide glass-based optical system. IR transmission properties of these materials combined to their high refractive indices lead to advantageous properties for sensing. In this study, numerical simulations have been carried out to investigate the potentialities of sulfide glass from the GeGaSbS system as a coupling prism material. Then, an angular modulation SPR biosensor has been set up in the Kretschmann–Raether arrangement. Experimental data are consistent with numerical calculation and the detection limit of the sensor is 3 × 10⁻⁵ RIU. These preliminary results are promising. Further investigations have to be carried out to confirm the great potentialities of those materials for SPR-based biosensor.     

Optical fiber pH sensor based on lossy-mode resonances by means of thin polymeric coatings

This work describes the fabrication of an optical fiber sensor with spectral response to pH based on the deposition of a thin polymeric coating on an optical fiber core. If the thin polymeric coating has a high refractive index real part and a non-null imaginary part, this permits a coupling of light to the modes guided in the polymeric coating originating optical resonances. These resonances are named by some authors as lossy-mode resonances (LMR) or guided-mode resonances. Moreover, the location of the resonances in the optical spectrum varies as a function of the coating thickness and refractive index. Hence, the utilization of the well-known poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) pH sensitive polymeric coating that presents a variation of the thickness with the pH of the solution (known as swelling/deswelling behaviour) permits the fabrication of optical fiber pH sensors based on wavelength detection. The fabrication of ready-to-use devices requires considering several aspects such as the adequate polymeric coating thickness or the selection of the resonance to be monitored. As a result, LMR-based optical fiber pH sensors with accuracy of ±0.001 pH units and an average sensitivity of 0.027 pH units/nm within the range between pH 3 and pH 6 have been obtained after an adequate design.     

Detection of toluene dissolved in water by using PCS fibers excited by an inclined collimated beam

This paper reports results on the sensitivity of straight polymer-clad silica (PCS) detection fibers with short sensing parts coated with polysiloxane polymers to toluene dissolved in water. The detection was based on refractive index changes of the polymers induced by the penetration of toluene into them. These changes were detected by measuring changes of the output power from the detection fibers excited by an inclined collimated beam at 630 nm.

Commercially available Cablelite 950-701 and two types of polymethylphenylsiloxane polymers developed at the Romanian Academy were tested as materials for the fabrication of the detection part in the fiber cladding. These parts were prepared by application of polymer layers onto a bare silica core by a dip-coating technique. Layers with thicknesses of about 20 μm were prepared.

Examples of angular distributions of the output power determined for the detection polymers in contact with air, time response curves measured with the detection parts brought into contact with aqueous solutions of toluene under different hydrodynamic conditions, and sensitivity curves are shown in the paper. The best detection limit of about 10 mg/l of toluene, reversibility and linearity of the fiber response in a range 0–100 mg/l could be achieved with fibers coated with Cablelite 950-701 polymer.     

Novel U-shape gold nanoparticles-modified optical fiber for localized plasmon resonance chemical sensing

A novel fiber-optic localized plasma resonance (FO-LPR) sensor composed of a U-shape optical fiber was proposed and demonstrated in this study. The U-shape optical fiber was fabricated by a femtosecond laser micromachining system. The dimensions of the U-shape zone were 100 μm in depth measured from the surface of the polymer jacket layer, 80 μm in width in the jacket layer, 60 μm in width in the cladding layer. The total length is 5 mm. After laser annealing treatment, the average surface roughness was 205.8 nm as determined by Atom Force Microscope (AFM). The exposed surface of the U-shape fiber was modified with self-assembled gold nanoparticles to produce the FO-LPR sensor. The response of the sensor shows that the signal increases linearly with increasing refractive index. The sensor resolution of the sensor was determined to be 1.06 × 10⁻³ RIU.     

LiNbO3棱镜耦合双金属薄膜表面等离子共振传感器

高折射率铌酸锂(LiNbO3)(2.202)为棱镜耦合激发的角度调制型表面等离子共振传感器,利用反射率公式优化单层银膜、金膜和双层银/金膜传感器薄膜的厚度,分别计算了优化厚度的传感器在检测样品折射率为1.330时的共振角、灵敏度、峰值半宽度(FWHM)和品质因数(FOM),理论计算表明:双层金属薄膜,随着金膜厚度的增加,传感器灵敏度增加,但峰值半宽度增加,品质因数下降.综合考虑,选择银/金(41/5)优化组合,传感器品质因数为优化的单层金膜(47 nm)传感器品质因数的2倍以上,另外,与常用的BK7玻璃棱镜耦合相比,LiNbO3棱镜耦合具有较大的样品动态检测范围.优化厚度的传感器实验检测糖水浓度表明:糖水浓度与共振角为线性比例关系.     

Full-field surface plasmon resonance sensor for high resolution refractive index measurement using common-path heterodyne interferometer

This study presents a full-field surface plasmon resonance (SPR) sensor induced by attenuated total reflection (ATR)-couple for liquid refractive index measurement. The system adopts a common-path heterodyne interferometer to measure the phase difference between P- and S-wave after passing through the SPR sensor. In order to realize the full-field measurement, it adopts a three-frame integrating-bucket method. The experimental results show great consistency profile between single point and full-field liquid refractive index measurement from 1.330 to 1.340 RIU. It shows that the best sensitivity and resolution of a single pixel in charge couple device (CCD) for liquid refractive measurement are 3.3 × 10⁴ (deg/RIU) and 3.53 × 10⁻⁶ (RIU), respectively. As compared with traditional single-point method, the proposed method with a regular CCD has no degradation. Therefore, the system has many applications in chemistry and biology.     

A low-cost inductive proximity sensor for industrial applications

In this paper, we present an inductive proximity sensor with fully integrated electronics. The sensor with the compact hybrid configuration is composed of a sensing flat coil and an integrated electronic interface. We focused during the development on the temperature stability and robustness of the sensor by keeping its low-fabrication cost. The sensor exhibits a longitudinal resolution of 120 nm for an aluminum target position up to 500 μm from the sensing coil with the side size of 3.5 mm. The temperature drift of the sensor is less than 700 ppm/°C for the same range of the target position. The total working range is from 100 to 1500 μm. The sensor power consumption is 100 mW and the active sensor dimensions are 3.5 mm×3.5 mm×1.2 mm. We also showed the facility of the sensor packaging. This kind of integrated sensor has the potential for even more industrial applications.     

多模光纤光栅的应变传感特性

主要对多模光纤光栅的应变传感特性进行了实验研究,实验结果表明,光纤光栅的Bragg波长随轴向应变的变化呈现出良好的线性关系,而且其重复性相当好。实验测得的应变灵敏度为0.0011nm/(×10-6),与理论计算值相符。这些特性与单模光纤光栅的传感特性基本相同,因此可以用多模光纤光栅代替单模光纤光栅制作光纤传感器以降低成本。实验结果可以作为对光纤光栅进一步深入研究的参考。