空芯光子晶体带隙光纤用于甲烷检测的研究

基于甲烷的光谱吸收理论,设计了一套利用空芯光子晶体带隙光纤(HC-PBGF)做传感气室的全光纤甲烷检测系统。根据HITRAN2012数据库和HAWKS软件确定甲烷的检测波长;利用气泵在HC-PBGF两端形成压力差来加快甲烷气体的扩散,利用反射镜延长光程至2倍;通过实验得到190s后气体扩散完成,0.5h内系统示值波动为0.012%,平均重复率为99.63%。最后配制0~2.5%浓度的甲烷气体进行浓度检测,得出甲烷浓度与相对吸收强度呈线性关系,线性度为99.92%。该系统成功实现了将HC-PBGF的空芯结构用于甲烷的吸收检测,加快了系统的响应速度,实现了仪器的小型化,使在线检测更加方便。     

天津大学光纤传感技术研究部分最新进展

本文介绍了天津大学在光纤传感技术研究领域的最新进展.主要为:基于白光干涉实现了非本征光纤法珀和FBG并行解调,法珀腔长测量误差0.81 μm,FBG波长测量误差14 pm;基于光纤有源内腔结构夹现了乙炔气体传感,灵敏度优于100ppm;基于保偏光纤实现了分布式传感,灵敏度可达6 cm;基于边缘滤波器开发了光纤光栅解调仪,波长分辨力可达1.2pm,扫描速率超过200kHz;采用全光纤OCT技术实现了牙齿模型的二维、三维扫描;实现了光纤陀螺光纤环的温度、振动等动态特性检测.     

Nanocrystal Skins with Exciton Funneling for Photosensing

Highly photosensitive nanocrystal (NC) skins based on exciton funneling are proposed and demonstrated using a graded bandgap profile across which no external bias is applied in operation for light‐sensing. Four types of gradient NC skin devices (GNS) made of NC monolayers of distinct sizes with photovoltage readout are fabricated and comparatively studied. In all structures, polyelectrolyte polymers separating CdTe NC monolayers set the interparticle distances between the monolayers of ligand‐free NCs to <1 nm. In this photosensitive GNS platform, excitons funnel along the gradually decreasing bandgap gradient of cascaded NC monolayers, and are finally captured by the NC monolayer with the smallest bandgap interfacing the metal electrode. Time‐resolved measurements of the cascaded NC skins are conducted at the donor and acceptor wavelengths, and the exciton transfer process is confirmed in these active structures. These findings are expected to enable large‐area GNS‐based photosensing with highly efficient full‐spectrum conversion.     

Cavity-ring-down principle for fiber-optic resonators: experimental realization of bending loss and evanescent-field sensing

A novel measurement principle for fiber-optic sensing is presented. Use of a cavity-ring-down scheme enables measurements of minute optical losses in high-finesse fiber-optic cavities. The loss may be induced by evanescent-field absorption, fiber bending, fiber degradation, Bragg gratings, or any other effect that might change the fiber transmission or cavity reflector properties. The principle is proved to be rather insensitive to ambient perturbations such as temperature changes. A high-sensitivity measurement of loss due to bending is presented as a proof-of-principle. With a cavity finesse of 627 a sensitivity for induced loss of 108 ppm (4.68 x 10(-4) dB) is achieved. Preliminary measurements of evanescent-field absorption are also discussed.     

Laser diode for remote sensing of methane

This paper examines an approach to the remote sensing of explosion-safe methane concentrations using optical fiber and demonstrates that considerable potential is offered by a system for the remote sensing of methane using a laser diode emitting at 1655 nm. We describe a novel procedure for the growth of epitaxial buried InGaAsP/InP heterostructures for 1655-nm lasers. Single-mode 1655-nm laser diodes have been produced and their parameters have been studied. It is shown that the diodes can be employed in real systems for remote monitoring of methane.     

Measuring Humidity in Methane and Natural Gas with a Microwave Technique

The results of microwave measurements with a quasi-spherical resonator in humid methane samples realized under laboratory conditions at the Istituto Nazionale di Ricerca Metrologica (INRiM) and under industrial conditions in a natural gas sample made available at the facilities of the Technical Manager of the Spanish Gas System and main supplier of natural gas in Spain (ENAGAS) are reported. Measurements at INRiM included vapor phase and condensation tests on methane samples prepared with amount fractions of water between 600 ppm and 5000 ppm at temperatures between 273 K and 295 K and pressures between 150 kPa and 1 MPa. ENAGAS measurements were performed at ambient temperature, 750 kPa on natural gas sampled from the pipeline and successively humidified at amount fractions of water between 140 ppm and 250 ppm for completeness of the comparison with several humidity sensors and instrumentation based on different technologies. To enhance the sensitivity of the microwave method at low humidity, an experimental procedure based on the relative comparison of the dielectric permittivity of the humid gas sample before and after being subject to a chemical drying process was conceived and implemented. The uncertainty budget and the final sensitivity of this procedure are discussed.     

In situ growth of Prussian blue nanocubes on polypyrrole nanoparticles: facile synthesis,characterization and their application as fiber optic gas sensor

Polypyrrole (PPy) and polypyrrole/Prussian blue (PPy–PB) nanocomposite-based fiber optic gas sensors are developed for gas sensing application. Prussian blue (PB) nanocubes are successfully grown on polypyrrole (PPy) nanoparticles by in situ oxidative polymerization method to obtain PPy–PB nanocomposite. PPy and PPy–PB are evaluated based on structural, morphological and electrical properties. The characteristic peaks present in the FTIR spectra of pure PPy and PB nanoparticles are also present in the FTIR spectrum of PPy–PB nanocomposite with small shifts in the absorption maximum. The XRD pattern reveals the semicrystalline structure of PPy–PB nanocomposite with an average crystallite size of 22 nm, and the morphology (FESEM) shows the formation of PB nanocubes over PPy matrix. AC conductivity measurements show slight improvement in the conductivity value of PPy–PB in comparison with PPy. Dielectric studies in the frequency range of 50 Hz–5 MHz reveal that PPy–PB nanocomposite is a high-k dielectric material. At 50 Hz, PPy–PB exhibits high dielectric constants of 1149 and 766 with low dielectric loss values of 9.9 and 4.6 at 150 and 120 °C, respectively. Further, their application as fiber optic gas sensors in sensing various gases is studied using fiber optic technique. The spectral response is studied for various concentrations (0–500 ppm) of ammonia, acetone and ethanol gases at room temperature. The study shows that the spectral intensity increases linearly with different concentrations of all gases. The clad-modified fiber optic sensor with PPy–PB nanocomposite exhibits enhanced sensitivity for ethanol than clad-modified fiber optic sensor with PPy nanoparticles. TGA studies reveal the high thermal stability of PPy–PB nanocomposite. Hence, PPy–PB-based fiber optic sensors can be used to sense toxic ethanol vapor not only at room temperature but also in a composite environment where a temperature variation is expected.     

Core-offset hollow core photonic bandgap fiber-based intermodal interferometer for strain and temperature measurements

A novel core-offset hollow core photonic bandgap fiber (HCPBF) based intermodal interferometer is presented. It is fabricated by splicing a section of HCPBF between two single mode fibers with a slight core offset at one splice joint. The fabrication process only involves splicing and cleaving. Its applications for strain and temperature measurements are also demonstrated. Its strain and temperature sensitivities are -1.17 pm/με and 6.66 pm/°C, respectively.     

Detection of acetone vapor using graphene on polymer optical fiber

Recently, many studies have been focused on the development of fiber optic sensor systems for various gases and vapors. In the present study, an intrinsic polymer optical fiber (POF) sensor using graphene is described for the purpose of acetone vapor sensing for the first time. Observations on the continuous measurement of acetone vapor in dehydrated air are presented. The principle of operation of sensor transduction relies on the dependence of the reflectance on the optical and geometric properties of the sensitive over layered when the vapor molecules are adsorbed on the graphene film. For the same purpose the CVD synthesized graphene film was transferred on the POF end. The synthesized graphene film thickness was evaluated using atomic force microscopy (AFM), Raman spectroscopy and transmission electron microscopy (TEM). For the preliminary evaluation using volatile organic compounds, we evaluated the sensor performance for acetone. Upon the interaction of the sensor with acetone vapor, the variation in the reflected light was monitored as a function of the acetone concentration. The sensor response shows a significant change in sensitivity as compared with the POF probe without a graphene coating. The present sensor shows a satisfactory response upon exposure to various concentrations of acetone vapor from 44 ppm to 352 ppm. To the best of our knowledge, the use of graphene film along with POF for the sensing of volatile organic compounds has not previously been reported.     

Development of electrodeposited ZnTe layers as window materials in ZnTe/CdTe/CdHgTe multi-layer solar cells

Zinc telluride (ZnTe) thin films have been deposited on glass/conducting glass substrates using a low-cost electrodeposition method. The resulting films have been characterized using various techniques in order to optimize growth parameters. X-ray diffraction (XRD) has been used to identify the phases present in the films. Photoelectrochemical (PEC) cell and optical absorption measurements have been performed to determine the electrical conductivity type, and the bandgap of the layers, respectively. It has been confirmed by XRD measurement that the deposited layers mainly consist of ZnTe phases. The PEC measurements indicate that the ZnTe layers are p-type in electrical conduction and optical absorption measurements show that their bandgap is in the range 2.10–2.20 eV. p-Type ZnTe window materials have been used in CdTe based solar cell structures, following new designs of graded bandgap multi-layer solar cells. The structures of FTO/ZnTe/CdTe/metal and FTO/ZnTe/CdTe/CdHgTe/metal have been investigated. The results are presented in this paper using observed experimental data.     

Refractometric sensor based on a phase-shifted long-period fiber grating

A refractometric sensor based on a phase-shifted long-period fiber grating written by electric-arc discharges is presented. Transmission and reflective configurations for refractive index measurements are studied. It is observed that the reflective topology permits better performance compared with the transmission one, which is the approach normally utilized in the context of long-period fiber sensing. The resolution achieved in the measurement of refractive index enables the application of this sensing head structure in demanding situations, such as the measurement of the level of salinity of water.     

Bandgap-assisted surface-plasmon sensing

Surface-plasmon resonance (SPR) is a sensing technique widely used for its label-free feature. However, its sensitivity is contingent on the divergence angle of the excitation beam. The problem becomes pronounced for compact systems when a low-cost LED is used as the light source. When the Kretschmann configuration with a periodically modulated surface is used, a bandgap appears in the surface plasmon dispersion relation. We recognize that the high density of modes on the edge of the surface-plasmon bandgap permits the coupling of a wider range of incidence angles of excitation photons to surface-plasmon polaritons than what is possible in the traditional Kretschmann configuration. Here, the numerical simulation illustrates that the sensitivity, detection limit, and reflectivity minimum of an amplitude-based SPR bandgap-assisted surface-plasmon sensor are almost independent of the divergence angle. Two different bandgap structures are compared with the Kretschmann configuration using the rigorous coupled-wave analysis technique. The results indicate that the bandgap-assisted sensing outperforms traditional SPR sensing when the angular standard deviation of the excitation beam is above 1 degree.     

Design of vibration-insensitive Sagnac fiber-optic current sensors using spun high-birefringence fibers

A novel fiber-optic current sensing element is proposed to enhance sensor performance using spun high-birefringence fibers. Such element includes three fiber sections. Two terminal sections with a varying spin rate along the fiber are utilized to replace the fiber quarter-wave plates, each converting the light polarization state from linear to circular and vice versa. The middle section with a uniform spin rate is utilized as the current sensing fiber that maintains the circular polarization state during the light propagation. The fiber is also wound into a special geometric structure so that the Sagnac phase shift can be inherently eliminated, and the sensing result does not depend on the position of the current conductor. The evolution of the light polarization state was analyzed using coupled-mode theory with different polarization state incidents in the sensing fiber. A sensor scheme based on this type of spun fiber is also proposed.     

基于1550nm的全固态PBG—PCF的设计

设计了一种三角晶格结构的全内反射型光子晶体光纤,并在其包层孔内分别填充折射率为n=1．55～3．35（△n=0．3）的介电材料,使其等效为全固态光子带隙型光子晶体光纤,利用全矢量平面波展开法对其带隙特性进行分析,发现随着折射率的增加,光子带隙的位置逐渐向长波方向移动,导模也越来越少。设计一种工作波长为1550nm的全固态光子带隙型光子晶体光纤,计算得到其对应的归一化传播常数β=8．2时,导模的宽度大约为100nm。该光纤在光电转换或者电光转换等方面具有潜在的应用价值。     

Substrate geometry-dependent nonlinear absorption of carbon nanotubes deposited onto D-shaped optical fibers

The effect of single-wall carbon nanotubes (SWNTs) on nonlinear optical absorption of D-shaped fibers with versatile the remaining length of the cladding region and the interaction length are investigated. The optical absorption based on SWNTs is induced by the energy bandgap in SWNTs. The bandgap energy depends on the tube diameter of SWNTs. After fabricating versatile D-shaped fiber, SWNTs are deposited on the polished surface of D-shaped fibers. The cladding region of single mode fibers is removed by a side-polishing technique and the D-shaped fiber is obtained. In the D-shaped fiber, the cladding region is thin enough to induce the evanescent field coupling of core mode to the other modes of the SWNT-overlay. The nonlinear absorption based on the SWNTs-overlay is changed by the remaining length of cladding region and the interaction length because the coupling strength of evanescent field strongly depends on the different remaining lengths of the cladding region and the interaction lengths as well.     

波导式气体吸收池时间响应特性

波导式光学吸收池在气体浓度测量等领域有广泛的应用前景.本文理论分析了在普通扩散环境和压差环境下波导式光学吸收池的时间响应机理和特性,并搭建了相应的传感系统,优化系统结构进行了实验验证.通过对低浓度的甲烷和甲苯气体的测量实验,验证和修正了响应时间的理论模型.实验结果表明,优化系统在可以大幅降低响应时间的同时,保持较高的灵敏度,为波导式吸收池的设计与优化提供了重要的参考.     

Bragg scattering from an obliquely illuminated photonic crystal fiber

Scattering at visible frequencies from a two-dimensional silica/air photonic crystal material in the form of a fine fiber reveals the hexagonal crystal structure of the material. Oblique illumination allows the observation of first-order Bragg conditions even for a crystal structure with a pitch several times the wavelength of light. These scattering measurements demonstrate the feasibility of a low-loss waveguide based on photonic bandgap effects.     

Clad-modified fiber optic sensor utilizing CdS nanoflower as cladding for the detection of ethanol

Nowadays, sensing and detection of ethanol is paramount one for numerous applications including production of ethanol, fuel processing, chemical processing in industry, traffic management, food package testing for safety and medical applications. On the other hand, the rapid growth of nanotechnology paves the way to develop highly sensitive, portable and low-cost sensors with less power consumption. In line with this fact, a cladding modified fiber optic ethanol sensor using CdS nanoflower has been reported in the present study. CdS nanoflower was prepared by one step hydrothermal synthesis and subjected for various characterization techniques to investigate the material properties. The sensor probe was developed viz cladding modification technology followed by dip coating of CdS nanoflower over an unclad section of an optical fiber. The potency of CdS nanoflower has been probed for 0–300 ppm of acetone, ethanol, methanol and isopropanol at ambient environment. The sensing results demonstrates that the sensor coated with CdS nanoflower manifested better sensing performances towards ethanol (~?4.6% at 300 ppm) with response/recovery of 90 s and 100 s than other gases. The unique sensing feature complied that CdS nanoflower is desirable candidate in effective quantification of ethanol.

     

Single Pixel Black Phosphorus Photodetector for Near‐Infrared Imaging

Infrared imaging systems have wide range of military or civil applications and 2D nanomaterials have recently emerged as potential sensing materials that may outperform conventional ones such as HgCdTe, InGaAs, and InSb. As an example, 2D black phosphorus (BP) thin film has a thickness‐dependent direct bandgap with low shot noise and noncryogenic operation for visible to mid‐infrared photodetection. In this paper, the use of a single‐pixel photodetector made with few‐layer BP thin film for near‐infrared imaging applications is demonstrated. The imaging is achieved by combining the photodetector with a digital micromirror device to encode and subsequently reconstruct the image based on compressive sensing algorithm. Stationary images of a near‐infrared laser spot (λ = 830 nm) with up to 64 × 64 pixels are captured using this single‐pixel BP camera with 2000 times of measurements, which is only half of the total number of pixels. The imaging platform demonstrated in this work circumvents the grand challenges of scalable BP material growth for photodetector array fabrication and shows the efficacy of utilizing the outstanding performance of BP photodetector for future high‐speed infrared camera applications.     

Combined time- and wavelength-division-multiplexing demodulation technique of fiber grating sensor arrays using a tunable pulsed laser

Combined time- and wavelength-division-multiplexing demodulation technique of fiber Bragg grating (FBG) sensor arrays using a tunable pulsed laser is proposed and demonstrated. A tunable fiber laser based on a matched FBG is applied. The wavelengths of the sensing FBGs are obtained by detecting the maximum voltages with a photodiode that avoids the complex demodulation process. The advantages of this scheme are simple structure, high signal-to-noise ratio, and the sensing signals obtained by detecting the maximum voltages.