Optical Fiber Array Research Articles

基于相位调制的光纤干涉型光学相控阵扫描特性研究

基于相位调制的光纤干涉型光学相控阵扫描特性研究

用于指向光源的侧面发光塑料光纤阵列设计

用于指向光源的侧面发光塑料光纤阵列设计

Implementation of frequency and phase synchronization of fiber-optic hydroacoustic sensors array

Subject of Research.The problem of synchronization in arrays of distributed fiber-optic hydroacoustic sensors is considered. It is shown that noise floor level is one of the most important factors affecting the operation of the sensors. The maximum allowable level of phase noise arising from the operation of the synchronization system is determined. The main existing methods of synchronization are considered, and their influence on phase noise level is estimated. Method. The signal resampling method was used as the approach for signal synchronization task. Mathematical modeling of that method in the MATLAB environment was performed. It was shown that the addition of samples to the studied signal leads to a significant increase in phase distortion. Main Results. The impact of the clock frequency instability at the signal skew in the absence of synchronization system is numerically estimated. In case of ± 20 ppm generator clock frequency deviation, the skew reaches one second after 7 hours of work. It is shown that when 8 samples per second are added to the synchronized signal, spectral distortions reach the order of 100 µrad/Hz1/2. A hardware synchronization method is proposed that provides the possibility to increase the synchronization accuracy without distortion of the spectral and phase characteristics of the signal. The method is realized by adjusting local clock frequency generator involving feedback signal. Practical Relevance. The paper proposes two synchronization methods that allow for application of the Ethernet interface according to the IEEE 802.3 standard aimed at the implementation of the distributed sensor system synchronization. The paper presents an analytical and experimental evaluation of phase jitter value between different channels of the measuring system. These methods can be used in other distributed systems, where there is an urgent task of synchronization of its nodes while maintaining scalability and flexibility of the entire system.

Precisely Automatic Time Window Locating for an Interferometric Fiber-Optic Sensor Array Based on a TDM Scheme.

Interferometric fiber-optic sensors are often organized in the form of large-scale arrays by lending the technique of time division multiplexing (TDM) to reduce the system cost. Discriminating the time windows for different sensor units is the prerequisite to successfully demodulate the sensing message, but it traditionally calls for a very time-consuming manual calibration process. To combat this problem, a novel automatic time window locating method is proposed in this paper. It introduces the concept of shape function and carries out the cross-correlation operation between the shape function and the sensor signal. The shape function is defined as the function whose curve profile reflects the main data characteristics of the sensor signal. The time window information is then extracted from the correlation result. This whole process is carried out automatically by the interrogation controller of the sensor system without any manual intervene. Experiments are conducted to validate this method. The proposed method can greatly reduce the complexity of locating time windows in large-scale TDM sensor arrays, and make the practical use of the TDM scheme much more convenient.

Correction of Peak Tracking Ripple in Solid State Spectrometers

Errors in peak wavelengths from fiber Bragg gratings (FBGs) when monitored using a pixel-based solid state spectrometer have been investigated. These errors show a pseudo-sinusoidal ripple superimposed upon the expected linear response. The error is analogous to a peak-locking effect common to subpixel resolution particle tracking by CCD camera in particle image velocimetry. The amplitude of the error is calibrated as a proportion of the scaled variation of the change in the peak power of the calculated peak as the spectral peak is scanned across the pixel array. An error correction algorithm has been developed and verified in order to provide an increase in the accuracy of sensing solutions when using pixel-based spectrometers. The methods presented here permit the correction of pixel induced ripple errors in real time using data commonly available from many interrogation spectrometers. Calibration prior to use can be achieved by scanning each FBG spectral peak across the width of a single pixel. The proposed method of error correction is applied to a fiber optic sensor array utilized for biomedical pressure and temperature measurement and demonstrates a clear ability to increase the accuracy of measured signals.

Feasibility Study of Anchored Fiber-Optic Strain-Sensing Arrays for Monitoring Soil Deformation beneath Model Foundation

High-accuracy deformation measurement is an essential part of geotechnical model testing, in which fiber-optic sensors have great potentialities. In this study, a 1-g plane-strain model test was performed to investigate the feasibility of using fiber Bragg grating (FBG) strain-sensing arrays for monitoring soil deformation beneath a strip footing. The FBG array with specially made anchors was designed to enhance the fiber-soil interfacial bond and, hence, to improve the measurement quality. Three arrays were embedded horizontally within the soil to monitor internal linear strains, while digital photography-based particle image velocimetry (PIV) was employed to obtain superficial displacement and strain fields. Test results show that the strains captured by FBGs were comparable with equivalent strains determined via PIV analyses in terms of strain development, which reflected the evolution of soil deformation under incremental loads. Finally, the benefits and drawbacks of anchored FBG arrays for monitoring laboratory-scale models were discussed, with the conclusion being that they are capable of capturing internal strains or a strain profile of soil with low noise and high resolution, but there has to be a trade-off between robustness and sensitivity.

Humidity sensor based on micro optical fiber array fabricated by electrospinning

This paper reports a new type of humidity sensor based on aligned microfibers array waveguides with high specific surface area for the sensing region. The MNF array is fabricated by electrospinning and light can be efficiently coupled into them. The results indicate that the microfiber waveguides have uniform diameter and smooth morphology. Simultaneously, the microfiber array present obvious humidity sensing properties through strong evanescent fields for the humidity of 35–85 RH % with short response time, good linearity, stability and repeatability. Significantly, this idea provides an efficient and simple way to achieve a large number of optical waveguides array in microscopic scale with excellent optical characteristics and the microfibers could find wide applications in various micro or nano scale photonic and sensitive devices.

In-pipe fibre optic pressure sensor array for hydraulic transient measurement with application to leak detection

Controlled hydraulic transient pressure waves can be used to actively assess the condition of pressurised pipelines (e.g. leak detection). One practical challenge to the application of the technique to buried water pipelines is in the pressure measurement – fast-response pressure transducers are costly and the deployment is limited to one sensor per access point (e.g. at air valves or fire hydrants). The measurement from a single sensor is always the superposition of the waves travelling upstream and downstream along a pipe. It is often difficult to determine the direction of the propagating waves, unless there are suitable locations nearby where additional measurements can be made. The research reported here develops a fibre optic pressure sensor array for in-pipe transient pressure measurement. The sensor array consists of five Fibre Bragg Gratings (FBGs), each formed into a custom designed pressure transducer. The cable containing the array has a diameter of approximately 4 mm, making it easy to insert into a pipeline through a single access point for distributed transient pressure measurement. The usefulness of the fibre optic pressure sensors for transient-based pipeline leak detection is validated through laboratory experiments. The measurement from each individual fibre optic sensor is generally consistent with conventional piezo-resistive pressure transducers over a wide frequency range. The sensor array configuration enables the determination of the directional information of waves, therefore enhancing the ability of pipeline defect detection and localisation.

Self-Referenced Accelerometer Array Multiplexed on a Single Fiber Using a Dual-Pulse Heterodyne Phase-Sensitive OTDR

We report a new type of multiplexed fiber-optic accelerometer array based on a dual-heterodyne-pulse phase-sensitive OTDR technique. This scheme significantly simplifies the structure of fiber accelerometer and can greatly benefit its practical applications. The sensitivity model for the new type accelerometer based on the Rayleigh backscattering is developed for the first time, which shows a great difference from the transmission-type interferometric accelerometer. On a single piece of telecommunication fiber, we demonstrate the multiplexing of three accelerometers separated by 20 m, each with a measured sensitivity of ∼36 rad/g that agrees well with the theoretical analysis. The connecting fiber between accelerometers simultaneously acts as a distributed acoustic sensor, which under proper vibration isolation can be used as a self-reference to suppress system noises. We show that the common-mode noises of the sensor can be suppressed by 35 dB at a frequency of 100 Hz without using additional reference interferometers.

A portable high-resolution microscope based on combination of fiber-optic array and pre-amplification lens

A portable high-resolution microscope based on combination of fiber-optic array (FOA) and pre-amplification lens, which can overcome the magnification limit of FOA, was developed. By employing the amplification lens at the small-end of the FOA, the resolution was improved from 4.4 μm to 1.0 μm over a field of view (FOV) of 140 μm × 100 μm without using any algorithm processing, and the distortion only slightly increases from 0.13% to 0.19%. The distortion is still lower than that of normal lens-based microscopy. Moreover, the combination methods of the amplification lens and FOA were investigated, which including only FOA, the pre-amplification lens at the small-end of the FOA (termed preAL-FOA) and the post-amplification lens at the big-end of FOA (termed postAL-FOA). The result proved the best resolution was achieved by using the preAL-FOA This microscopy is suitable for real-time monitoring of cells in microfluidic systems.

Liquid Biopsy in the OMICS Era of Tumor Medicine

Liquid biopsy uses noninvasive blood test to assess tumor heterogeneity and evolution in real time. It looks for tumor components in the blood circulation, such as circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA), to provide tumor-specific information. By detecting multiplex tumor biomarkers, including nucleic acids, proteins, carbohydrates, and other tumor-derived substances, liquid biopsy helps with early tumor diagnosis, tumor evolution monitoring, and prognosis prediction. With the development of high-throughput OMICS tools like carbohydrate microarray and high-speed fiber-optic array scanning technology (FAST scan), it is now practical to identify glycan markers of CTCs and cancer stem cells (CSCs), especially those that are cell-surface exposed and readily accessible for immune recognition and targeting. Potential of this class of biomarkers in tumor subtyping and targeted immunotherapy is yet to be explored.

A Seismic Shift in Scalable Acquisition Demands New Processing: Fiber-Optic Seismic Signal Retrieval in Urban Areas with Unsupervised Learning for Coherent Noise Removal

With the development of fiber-optic seismic acquisition systems, dense seismic monitoring of the near surface in urban areas is quickly becoming much easier than ever before. We provide a case study illustrating the use of data from a new type of deployment, a fiber-optic array in existing telecommunications conduits underneath the Stanford University campus in California. We perform cross correlations of strain-rate measurements of the ambient wavefield to extract signals that mimic the response of the array to virtual active seismic sources at any receiver location. Now that we can so easily use our telecommunications infrastructure for continuous, dense, urban seismic acquisition, data collected in such a manner will go to waste unless we significantly automate ambient noise processing. We analyze 37 days of ambient noise; introduce an exploratory data analysis tool that clusters a week of noise to help us quickly find coherent, repeating noises that inhibit reliable extraction of useful signals; and design filters to remove nearby car recordings from the next 30 days of noise. We review a metric to quantify convergence of the cross correlations and use that metric extended throughout the array to support filtering out recordings of cars near the array.

Design and optimization of the fiber-optic probe array for measuring gas holdup in oil-gas-water multiphase flow

The exploitation of the mainland oilfield has entered a middle-late stage with high water-cut currently, and oil–gas–water multiphase flow exists commonly in exploitation of oilfield, accurate measurement of gas content has become a complex problem for the actual demand of dynamic monitoring in oil and gas field exploitation. In order to solve the problem of gas holdup measurement of the oil-gas-water multiphase flow in the oil-producing wells, this paper first constructed the mechanism model of a fiber-optic probe (FOP) for gas holdup measurement, and theoretically analyzed the feasibility of FOP to measure the gas holdup; simultaneously, the distribution characteristics of gas holdup for the upward oil-gas-water multiphase flow in a vertical pipe were simulated and analyzed by the FLUENT software; then the response characteristics of FOP piercing a gas bubble at different positions and different angles were analyzed. Secondly, the optimal structure of the fiber-optic probe array (FOPA) was optimized by analyzing the performance indexes of the ability to capture the cross-section gas holdup and the effect on the fluid flow interference. Finally, we designed and developed a FOPA-based logging instrument which could be applied to the complex environment of the oil-producing wells with high temperature, high pressure and narrow space. By the dynamic experiments carried out on the experimental facility of oil-gas-water multiphase flow and the onsite experiments carried out in Daqing Oilfield, the feasibility for the FOPA-based logging instrument to measure gas holdup was analyzed and verified.

Design of optical wavelength demultiplexer based on off-axis meta-lens.

We propose an off-axis meta-lens-based optical wavelength demultiplexer. The performance of the device initially proposed with four output channels (1527-1596nm, channel spacing 23nm) composed of an optical fiber array is analyzed by both scalar diffraction theory and ray tracing method. The results show that the fiber energy coupling efficiency of the demultiplexer could be larger than 89% and the channel bandwidth is about 9nm. Influences of the two key parameters, focal length f and off-axis angle α, are also investigated. We find that the minimum spectral linewidth of the channel is inversely proportional to the sine of α and nearly independent of f for a meta-lens with large F-number (F>5), while the effective spectral range is negatively (positively) dependent on α (f). These results are significant in guiding us to build small and compact demultiplexing devices for optical telecommunication.

High-quality hybrid TDM/DWDM-based fiber optic sensor array with extremely low crosstalk based on wavelength-cross-combination method

A high-quality hybrid time-division-multiplexing (TDM)/dense wavelength-division-multiplexing (DWDM)-based fiber optic sensor array with extremely low crosstalk is proposed and experimentally demonstrated in this paper. The array is based on a novel wavelength-cross-combination (WCC) method, aiming to combat the annoying problem of crosstalk between adjacent sensors. The core idea of this method is to reassign optical pulses of different wavelengths rather than of the same wavelength to the same photodetector to eliminate the possibility of coherent optical pulse overlapping and interference. Based on the WCC method and a so-called rectangular-pulse binary phase demodulation scheme, a sensor array with 4 TDM time windows and 16 DWDM wavelengths is set up and experimentally tested. Test results show that even utilizing an optical pulse modulator with less than 28 dB extinction ratio, the obtained crosstalk between adjacent sensors can be still suppressed down to less than −60 dB. This method provides an excellent choice for a practical sensor array application where the sensing performance is of the top consideration.

Fingertip Fiber Optical Tactile Array with Two-Level Spring Structure.

Tactile perception is a feature benefiting reliable grasping and manipulation. This paper presents the design of an integrated fingertip force sensor employing an optical fiber based approach where applied forces modulate light intensity. The proposed sensor system is developed to support grasping of a broad range of objects, including those that are hard as well those that are soft. The sensor system is comprised of four sensing elements forming a tactile array integrated with the tip of a finger. We investigate the design configuration of a separate force sensing element with the aim to improve its measurement range. The force measurement of a single tactile element is based on a two-level displacement that is achieved thanks to a hybrid sensing structure made up of a stiff linear and flexible ortho-planar spring. An important outcome of this paper is a miniature tactile fingertip sensor that is capable of perceiving light contact, typically occurring during the initial stages of a grasp, as well as measuring higher forces, commonly present during tight grasps.

Carbon nanotube-based magnetic bucky gels in developing dispersive solid-phase extraction: application in rapid speciation analysis of Cr(VI) and Cr(III) in water samples

ABSTRACTIn this work, we developed dispersive solid-phase extraction method with the use of carbon nanotube based magnetic bucky gels. The hydrophilic carbon nanotube (CNT)-based magnetic bucky gels (M-BGs) were developed with the features of magnetic susceptibility to permit fast injection of sorbent, rapid retrieval of the sorbent and high dispersion of MWCNT in the aqueous sample. We combined magnetic multi-wall carbon nanotube nanocomposite (MMWCNTs) with hydrophilic ionic liquids in order to prepare highly stable carbon nanotube-based magnetic bucky gels. The hydrophilic ILs act simultaneously as modifier and disperser for MMWCNTs and reduce the agglomeration of sorbent in water .Consequently they enhance the extraction efficiency. We used the unique features of this responsive gel (fluidity, stability, magnetic properties, and strong sorbing ability) in developing a new, fast, sensitive, simple, and environmental-friendly magnetic bucky gel-based dispersive solid-phase extraction method (M-BG-dSPE) combined with fibre optic linear array detection spectrophotometer (FO-LADS) for preconcentration and speciation of Cr(VI) and Cr(III) in water samples. The properties of MMWCNT and magnetic bucky gels were characterised by scanning electron microscopy (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and Fourier transform infrared spectrophotometer (FT-IR). Under the optimised conditions, the enrichment factor of the method was 318, the limit of detection was 0.1 ng mL−1 and the repeatability of the method, expressed as the relative standard deviation (RSD, n = 5), varies between 3.2% and 2.5% in different concentrations. The proposed procedure has been applied for speciation of Cr(VI) and Cr(III) in water samples with good recoveries in the range from 90 to 105%. Validation of the method was carried out by comparison of the obtained results with results obtained by the ET-AAS and spiking-recovery method.

High precision Fast Line Detection of alignment and coupling for planar Optical Waveguide device

Machine vision is widely used in alignment between planar optical waveguide chip and optical fiber array. Optical component edge detection is one of the key steps of machine vision in alignment. This paper has proposed a line detection algorithm based on the progressive probabilistic Hough transform (PPHT) and iteratively reweighted least squares (IRLS) algorithm for alignment between planar optical waveguide chip and optical fiber array. The experiment results show that the detection angle error is less than 0.005° and the time consumption is less than 0.5s through the proposed algorithm. Besides, it also can accurately fit optical component edge with some non-random factors. Therefore, the proposed new algorithm has the advantages of high precision, fast computing speed and good robustness, and it can successfully realize the high-precision fast line detection of optical component edge.

Fiber-coupled, UV-SWIR hyperspectral imaging sensor for combustion diagnostics.

A fiber-coupled, hyperspectral imaging sensor (HSIS) ranging from ultraviolet (UV) to short-wavelength-infrared (SWIR) wavelengths is developed for remote detection of planar [two-dimensional (2D)], spectrally resolved flame emission. The key component of the sensor is a dimension-reduction 2D-to-1D (one-dimensional) fiber-optic array that contains 1024 fibers and features high-UV optical transmission (>30% transmission at 310-340 nm, >90% at 340-2000 nm), wide operational wavelengths (300-2400 nm), and a compact and robust design (full length <5 cm). The flame-emission signals are transmitted to the remote HSIS through a 3-m-long, UV-grade, imaging fiber bundle that consists of 30,000 single-mode fibers. The design of the 2D-to-1D fiber array, the fiber-characterization process, and the sensor development are discussed in detail. 2D spectrally resolved measurements of CH*, OH*, and C2* distribution are made in premixed laminar flames. Improved chemiluminescence-based fuel/air ratio measurements using spectrally resolved detection are demonstrated. The results of the current study indicate that implementation of fiber-coupled HSIS is feasible in practical gas-turbine-engine test facilities with limited optical access.

Nocturnal Near-Surface Temperature, but not Flow Dynamics, can be Predicted by Microtopography in a Mid-Range Mountain Valley

We investigate nocturnal flow dynamics and temperature behaviour near the surface of a 170-m long gentle slope in a mid-range mountain valley. In contrast to many existing studies focusing on locations with significant topographic variations, gentle slopes cover a greater spatial extent of the Earth’s surface. Air temperatures were measured using the high-resolution distributed-temperature-sensing method within a two-dimensional fibre-optic array in the lowest metre above the surface. The main objectives are to characterize the spatio-temporal patterns in the near-surface temperature and flow dynamics, and quantify their responses to the microtopography and land cover. For the duration of the experiment, including even clear-sky nights with weak winds and strong radiative forcing, the classical cold-air drainage predicted by theory could not be detected. In contrast, we show that the airflow for the two dominant flow modes originates non-locally. The most abundant flow mode is characterized by vertically-decoupled layers featuring a near-surface flow perpendicular to the slope and strong stable stratification, which contradicts the expectation of a gravity-driven downslope flow of locally produced cold air. Differences in microtopography and land cover clearly affect spatio-temporal temperature perturbations. The second most abundant flow mode is characterized by strong mixing, leading to vertical coupling with airflow directed down the local slope. Here variations of microtopography and land cover lead to negligible near-surface temperature perturbations. We conclude that spatio-temporal temperature perturbations, but not flow dynamics, can be predicted by microtopography, which complicates the prediction of advective-heat components and the existence and dynamics of cold-air pools in gently sloped terrain in the absence of observations.