Laser Optical Sensor Research Articles

The development and applications of nanoporous gallium nitride in optoelectronics: a review

The development of nanoporous gallium nitride (NP-GaN) has widened the material properties and applications in third-generation semiconductor areas. NP-GaN has been used in laser emitters, light-emitting diodes, optical sensors, and optical energy storage devices. In this paper, we reviewed the most recent progress in the NP-GaN field by electrochemical etching. The etched GaN has many superior properties compared with original GaN templates, such as stronger photoluminescence intensity, thermal conductivity, piezo-electricity, more accessible area, stress relief, and refractive index. These advantages will make GaN more widely used in the field of optics and optoelectronics. Pore formation can be controlled by adjusting the applied potential and etching time. The NP-GaN makes the material of GaN have broader application prospects. We introduced in detail the application prospects of different GaN based processes and subsequent application methods in optoelectronics, sensors, and materials themselves. This review will help to improve further development of NP-GaN applications.

Optofluidic laser sensor for the detection of dopamine

Dopamine (DA) is a biomarker of many psychiatric diseases, such as schizophrenia and Parkinson's disease. Most current DA detection research adopts electrochemical method, which suffers interferences caused by many analogs with similar structures or redox potentials. To realize highly sensitive and selective DA sensing, herein we propose an optofluidic-laser-based DA sensor. Via the competitive adsorption mechanism, rhodamine 6G (Rh6G) is fixed on graphene oxide (GO) and replaced by DA in the sample, with the re-excited Rh6G serving as the gain medium of the optofluidic laser. As the DA concentration increases, more Rh6G is released into the sample, which induces an increase in the relative slope efficiency of the optofluidic laser and a reduction in the laser threshold. Both the relative slope efficiency and threshold attain a suitable linear relationship with the DA concentration within the 5–800 μM range. Under ideal circumstances, the detection limit of the biosensor is 0.3 µM. Moreover, the optofluidic laser-based biosensor achieves favorable selectivity for DA detection, proving the advantages of using optical laser sensors for DA detection in complex samples.

Uniform all-solid chalcogenide Bragg fiber with wide photonic bandgap via extrusion

As the Bragg fiber can guide light by tuning the structure parameters of claddings, it is possible to improve the ability of laser-power transmission in the mid-infrared with effective omnidirectional reflection, but it usually suffers from the disturbance of the air core and functional bandgap. Here, the structural parameters of three pairs of periodic cladding layers were optimized by the plane wave expansion method, and the thickness of each layer is 3.36 µm, consisting of Ge20As20Se15Te45 and As2S3 glasses with a refractive index contrast of Δn = 0.8. The simulation results showed that a wide bandgap of 1.2 µm can be realized in the fiber after structural optimization. Then, a fiber preform was prepared via an improved stacked extrusion based on seven thickness-compensated glass plates. The experimental results show that the all-solid Bragg fiber has three pairs of uniform periodic cladding and an extra-large core. The superior optical fiber structure can also be well maintained in the whole fiber length, and the average ratio of each cladding thickness to the fiber diameter is kept nearly at 3:100. Finally, the fiber loss at 1.55 µm and 2.94 µm is 12 dB/m and 18 dB/m, respectively. In all, such a well-structured all-solid chalcogenide Bragg fiber would pave a new way to develop high-quality laser transmission or optical sensors in mid-infrared.

Research on on-line assembly and calibration system based on laser scanning and optical fiber sensor

In order to improve the degree of assembly automation, an online assembly calibration system is designed based on laser scanning and optical fiber sensors. The optical fiber sensing module is used to obtain the stress field information, and the laser scanning module is used to obtain the point cloud information of the assembly structure. The position offset caused by the stress field can be compensated to the 3D point cloud for improving the target reconstruction accuracy. It consists of laser scanning module, optical fiber sensor module, demodulator, data analysis module, etc. Analyzing the structural characteristics of the module, the stress field distribution of the module structure is obtained through simulation analysis, and an appropriate optical fiber sensor network layout is constructed. When the force is applied in different directions, the stress field distribution of the assembly structure is simulated and analyzed. The results show that the magnitude and direction of the residual stress have an impact on the distribution of the stress field. At the same time, the stress field diffusion degree had been also analyzed in different strength conditions. In the calibration test of FBG sensor, the functional relationship between wavelength variation and stress is about 0.0011 nm/N. In the assembly test, the stress test trends of different FBGs were obtained, and the relative error was concentrated between 4.0% and 9.0%, which had good stability. After correcting the position of the point cloud for optical fiber sensing data, the position deviation between the test point and the digital analog has been significantly reduced, with the average value decreasing from 2.953. to 0.095 mm. It has good applicability in factories with large interference of working environment, and can improve the application field of intelligent assembly.

Multiplexed optical fiber cell temperature sensing system with high sensitivity and accuracy.

A multiplexed fiber laser sensing system for cell temperature is proposed. To the best of the authors' knowledge, this is the first multilongitudinal mode (MLM) optical fiber laser sensor array designed for cell temperature sensing. A two-channel cell temperature sensing system with high sensitivity and real-time sensing capability is achieved. The temperature change of human hepatoellular carcinomas (HepG2) cells under the influence of exogenous chemical aflatoxin B1 (AFB1) can be monitored in real time. A fiber laser cavity consists of a pair of fiber Bragg gratings (FBGs) with matched central wavelengths and a piece of erbium-doped fiber (EDF). The static FBG is utilized for design of fiber laser cavity and laser modes selection. In comparison, the sensing FBG is used for cell temperature sensing. The sensing FBG has a length of 10mm and a diameter of . Beat frequency signals (BFS) are generated by MLM lasers after optical-to-electrical conversion at a photodetector. Frequency change of a BFS is closely related to the reflected wavelength change of the sensing FBG. Through frequency division multiplexing, two fiber laser cavities are designed in the sensing system for two-channel temperature sensing. Frequency shift of a BFS that represents temperature change of cells can be automatically recorded in seconds. A two-channel cell temperature sensing system is designed with high sensitivities of 101.62 and , respectively. The temperature change of HepG2 cells under the influence of exogenous chemical AFB1 is monitored in real time. The proposed system has the advantages of simple structure, high sensitivity, and two-channel sensing capability. Our study provides a simple and effective method to design a fiber laser sensor system without complex demodulation techniques and expensive optical components.

Strain and curvature optical fiber laser sensor based on an accurate RI-regulated FMF with high modal power balance

In this paper, a ring fiber laser sensor based on a three layered-core few modes fiber (TL-FMF) is proposed. The home-made TL-FMF is spliced with two pieces of single mode fiber (SMF) at both sides as the sensing and filtering component. In the TL-FMF, an intermediate with higher refractive index (RI) is sandwiched between a central dip and a sub-high RI layer. Due to the special RI, the TL-FMF has an equidistant modal effective RI difference and a balanced modal power of different modes, enabling a highly uniform interference spectrum. Then applying the TL-FMF in proposed ring fiber laser sensor, the sensing experimental results show that its sensitivities in strain and curvature are −2.78 pm/με and −6.17 nm/m−1, respectively, and shows an excellent characteristic of temperature insensitivity. This fiber laser sensor implements the dual-parameter measurement with anti-cross sensitivity, which offers a promising candidate in fiber fabrication monitoring, deformation measurement and bending detection.

Self-Alignment Algorithm for Ring Laser Optical Sensor Based Strapdown Inertial Navigation Systems

Accurate establishment of initial alignment in shortest duration is vital to strapdown inertial navigation systems (SINS). In self-alignment, initial orientation is established by processing the sensor data itself without any external aid. This work addresses the implementation and performance assessment of self-alignment algorithm to obtain the initial orientation of a ring laser optical sensor based INS in stationary or near stationary condition. Lateral velocity error dynamics is utilized to address the alignment problem based on a Kalman filter approach. Performance is evaluated on lab data acquired on an angular motion simulator with known reference angles. The errors in level angle and azimuth computation are within 3 arcs and 250 arcs, respectively implying a high degree of accuracy. Algorithm also offers a fast convergence with alignment time required being less than 200 s making it ideal for all critical missions where initial self-alignment is a mandate to obtain the initial orientation in static or quasi-static condition.

Switchable single- and dual-wavelength thulium/holmium co-doped fiber laser with single-longitudinal mode output

A single-longitudinal-mode ring thulium/holmium co-doped fiber laser (THDFL) possessing the switchable single- and dual-wavelength outputs is proposed with two subring cavities and two polarization-maintaining fiber Bragg gratings. The switching operation is realized by tuning the pump power and polarization controller together. When the THDFL working at single-wavelength output state, the optical signal-to-noise ratio (OSNR) is ∼51 dB, and the maximum power and wavelength fluctuation within 1 h are 0.804 dB and 0.04 nm, respectively. Using the phase noise analysis-based linewidth measurement system, the linewidth is measured to be 0.16 MHz with a measuring time of 0.002 s. When the THDFL working at dual-wavelength output state, the OSNR is ∼55 dB, and the maximum power and wavelength fluctuation within 1 h are 0.802 dB and 0.05 nm, respectively. The proposed THDFL may find wide applications in microwave photonics generation and optical fiber laser sensor.

Experimental Characterization of Lithium-Ion Cell Strain Using Laser Sensors

The characterization of thickness change during operation of LFP/Graphite prismatic batteries is presented in this work. In this regard, current rate dependence, hysteresis behaviour between charge and discharge and correlation with phase changes are deepened. Experimental tests are carried out with a battery testing equipment correlated with optical laser sensors to evaluate swelling. Furthermore, thickness change is computed analytically with a mathematical model based on lattice parameters of the crystal structures of active materials. The results of the model are validated with experimental data. Thickness change is able to capture variations of the internal structure of the battery, referred to as phase change, characteristic of a certain state of charge. Furthermore, phase change shift is a characteristic of battery ageing. Being able to capture these properties with sensors mounted on the external surface the cell is a key feature for improving state of charge and state of health estimation in battery management system.

Twelve-Wavelength-Switchable Thulium-Doped Fiber Laser With a Multimode Fiber Bragg Grating

In this article, a precisely controlled, switchable thulium-doped fiber laser (TDFL) with high optical signal-to-noise ratio (OSNR) is proposed and demonstrated. A home-made multimode fiber Bragg grating (MMFBG) with multireflection peaks was used as an optical filter to select the desired lasing channel. Using a manually controlled fusion splicer, the axial misalignment was applied between the single mode fiber and the MMFBG to switch the output wavelength. In the experiment, the number of switchable lasing lines was up to 12, and the fluctuation of the center wavelength and output power was less than 0.03 nm and 0.67 dB, respectively. A maximum slope efficiency of 1.3% was obtained when the axial misalignment was 0 μm, and the OSNR was higher than 65 dB. In addition, the proposed fiber laser was used as an optical fiber laser sensor to quantify the strain applied on the MMFBG, and a sensitivity of 1.16 pm/μ∈ was obtained.

A portable three-component displacement measurement technique using an unmanned aerial vehicle (UAV) and computer vision: A proof of concept

This study proposes a new remote sensing technique to measure three-component (3C) dynamic displacement of three-dimensional (3D) structures. A sensing system with a UAV platform and contact-free sensors (e.g., optical and infrared (IR) cameras) is employed to provide a portable and convenient alternative to conventional approaches that require sensor installation on a structure. The original contributions of this study include (1) integrating both optical and IR cameras with a UAV platform to measure dynamic structural response, and (2) developing new data post-processing algorithms (based on target identification, Direct Linear Transformation, and active stereo vision) to simultaneously extract the 3C displacement of a 3D structure from optical and IR videos, which presents a unique advantage compared to the existing UAV-based displacement measurement techniques that allow the measurements in only one or two directions using optical cameras or laser sensors. The efficacy of the proposed technique is validated through laboratory experiments.

Design and evaluation of an integrated scanning laser triangulation sensor

This work presents the design, simulation, control and experimental result of an optical scanning laser sensor for 3D imaging. The system design satisfies the Scheimpflug condition even though only the illumination path is scanned by a compact fast steering mirror (FSM). To reconstruct the surface profile from measured quantities and model parameters, geometrical relations are used. The influence of a misalignment on the achievable resolution is determined, using ray-tracing simulations. To scan the area of interest an adapted scan trajectory is employed, such that a uniform spatial resolution is generated. The system captures the sample with 100 x 100 pixels and achieves a frametime of 10 s. The lateral scan area of 15 x 23 mm is obtained with a maximum lateral resolution of 60 µm. Through the optical scan the measurement time can be reduced by a factor of 400 compared to a mechanical scanning triangulation sensor system.

Determining the geometrical parameters of spring suspension of locomotives

AnnotationThe paper considers the issues of measuring the geometric parameters of the springs using a laser-optical sensor. The features of an automated rig for measuring the parameters of the springs are presented. The work also investigates the operation of the laser-optical sensor. The results obtained allow using the laser-optical sensor for measuring the geometric parameters of the springs of a rolling stock. The measurements obtained with the laser-optical sensor to determine the parameters of the locomotive suspension springs are presented.

Design and Implementation of an New 6-DoF Magnetic Levitation Positioning System

High-precision magnetic levitation positioning systems are of great interest for many modern applications, because of their absolutely non-contact operation and large planar travel ranges with precisions up to the nanometer range. In this article, a novel six degrees-of-freedom (6-DoF) magnetic levitation (maglev) system, which is based on repulsive levitation forces, is presented. Compared to other known solutions from the literature, this proposed concept allows a freely accessible mover from above in combination with decoupled levitation and propulsion forces. The maglev system consists of eight air-core coils in order to realize a 6-DoF motion. The six-axes position measurement is achieved by four eddy current sensors and four optical laser sensors. After a detailed explanation of the working principle, a decoupled 6-DoF dynamic model is derived and analyzed. Then, based on this dynamic model, simple proportional–integral–differential (PID) controllers are implemented in order to control the unstable behavior of the system. The aim of this article is to demonstrate the functionality of the proposed system. Thus, various experimental results, obtained from the prototype, were conducted to evaluate the dynamic performance of the maglev system. It will be shown that the position errors lie in the range of the sensor resolution and, thus, can be made as small as desired, depending on the applied sensor resolution.

Hybrid position and orientation tracking for a passive rehabilitation table-top robot.

This paper presents a real time hybrid 2D position and orientation tracking system developed for an upper limb rehabilitation robot. Designed to work on a table-top, the robot is to enable home-based upper-limb rehabilitative exercise for stroke patients. Estimates of the robot's position are computed by fusing data from two tracking systems, each utilizing a different sensor type: laser optical sensors and a webcam. Two laser optical sensors are mounted on the underside of the robot and track the relative motion of the robot with respect to the surface on which it is placed. The webcam is positioned directly above the workspace, mounted on a fixed stand, and tracks the robot's position with respect to a fixed coordinate system. The optical sensors sample the position data at a higher frequency than the webcam, and a position and orientation fusion scheme is proposed to fuse the data from the two tracking systems. The proposed fusion scheme is validated through an experimental set-up whereby the rehabilitation robot is moved by a humanoid robotic arm replicating previously recorded movements of a stroke patient. The results prove that the presented hybrid position tracking system can track the position and orientation with greater accuracy than the webcam or optical sensors alone. The results also confirm that the developed system is capable of tracking recovery trends during rehabilitation therapy.

Forced response of rotating bladed disks: Blade Tip-Timing measurements

The Blade Tip-Timing is a well-known non-contact measurement technique currently employed for the identification of the dynamic behaviours of rotating bladed disks. Although the measurement system has become a typical industry equipment for bladed disks vibration surveys, the type of sensors, the positioning of the sensors around the bladed disk and the used algorithm for data post-processing are still not standard techniques, and their reliability has to be proved for different operation conditions by the comparison with other well-established measurement techniques used as reference like strain gauges. This paper aims at evaluating the accuracy of a latest generation Tip-Timing system on two dummy blisks characterized by different geometrical, structural and dynamical properties. Both disks are tested into a spin-rig where a fixed number of permanent magnets excite synchronous vibrations with respect to the rotor speed. A new positioning for the Blade Tip-Timing optical sensors is tested in the case of a shrouded bladed disk. Due to the presence of shrouds, the sensors cannot be positioned at the outer radius of the disk pointing radially toward the rotation axis as in the most common applications, since the displacements at the tips are very small and cannot be detected. For this reason a particular placement of optical laser sensors is studied in order to point at the leading and trailing edges' locations where the blades experience the largest vibration amplitudes with the aim of not interfering with the flow path. Besides the typical Blade Tip-Timing application aimed at identifying the dynamical properties of each blade, an original method is here proposed to identify the operative deflection shape of a bladed disk through the experimental determination of the nodal diameters. The method is applicable when a small mistuning pattern perturbs the ideal cyclic symmetry of the bladed disk.

The application of a cavity ring-down spectrometer to measurements of ambient ammonia using traceable primary standard gas mixtures

A correction for the undesirable effects of direct and indirect cross-interference from water vapour on ammonia (NH3) measurements was developed using an optical laser sensor based on cavity ring-down spectroscopy. This correction relied on new measurements of the collisional broadening due to water vapour of two NH3 spectral lines in the near infra-red (6548.6 and 6548.8 cm−1), and on the development of novel stable primary standard gas mixtures (PSMs) of ammonia prepared by gravimetry in passivated gas cylinders at 100 μmol mol−1. The PSMs were diluted dynamically to provide calibration mixtures of dry and humidified ammonia atmospheres of known composition in the nmol mol−1 range and were employed as part of establishing a metrological traceability chain to improve the reliability and accuracy of ambient ammonia measurements. The successful implementation of this correction will allow the extension of this rapid on-line spectroscopic technique to exposure chamber validation tests under controlled conditions and ambient monitoring in the field.

Experimental identification of thermal induced warpage in polymer–metal composite films

Composite thick films consisting of multi-layered polymers and metals are widely used in integrated circuits(IC) and its packaging, and it arises intricate stress and warpage problems due to complex inner stress distribution and evolution. The wafer warpage origination and evolution of multi-layered polyimide (PI)/Cu composite film is measured in-situ by a Multi-beam Laser Optical Sensor (MOS) system. It's found that PI has an intricate influence on wafer warpage evolution and Cu plastic deformation due to viscoelasticity and glass-transition, and the influence differs in different structures and at different temperatures. Nonlinearity of the curvature–temperature curve of the composite occurs at much lower temperature than in single PI or Cu film, showing mutual effect of PI and Cu. Unlike bare or capping PI film that totally stress relaxed at high temperature, bottom PI coated by Cu film sustains a medium compressive stress, indicating that Cu coating film has restrained stress relaxation of PI. The warpage evolution during heating is different from that during cooling, perhaps due to different deformation mechanism.

Streptomycin Induced Stress Response in Salmonella enterica Serovar Typhimurium Shows Distinct Colony Scatter Signature.

We investigated the streptomycin-induced stress response in Salmonella enterica serovars with a laser optical sensor, BARDOT (bacterial rapid detection using optical scattering technology). Initially, the top 20 S. enterica serovars were screened for their response to streptomycin at 100 μg/mL. All, but four S. enterica serovars were resistant to streptomycin. The MIC of streptomycin-sensitive serovars (Enteritidis, Muenchen, Mississippi, and Schwarzengrund) varied from 12.5 to 50 μg/mL, while streptomycin-resistant serovar (Typhimurium) from 125–250 μg/mL. Two streptomycin-sensitive serovars (Enteritidis and Mississippi) were grown on brain heart infusion (BHI) agar plates containing sub-inhibitory concentration of streptomycin (1.25–5 μg/mL) and a streptomycin-resistant serovar (Typhimurium) was grown on BHI containing 25–50 μg/mL of streptomycin and the colonies (1.2 ± 0.1 mm diameter) were scanned using BARDOT. Data show substantial qualitative and quantitative differences in the colony scatter patterns of Salmonella grown in the presence of streptomycin than the colonies grown in absence of antibiotic. Mass-spectrometry identified overexpression of chaperonin GroEL, which possibly contributed to the observed differences in the colony scatter patterns. Quantitative RT-PCR and immunoassay confirmed streptomycin-induced GroEL expression while, aminoglycoside adenylyltransferase (aadA), aminoglycoside efflux pump (aep), multidrug resistance subunit acrA, and ribosomal protein S12 (rpsL), involved in streptomycin resistance, were unaltered. The study highlights suitability of the BARDOT as a non-invasive, label-free tool for investigating stress response in Salmonella in conjunction with the molecular and immunoassay methods.

A laser-optical sensor system for blade vibration detection of high-speed compressors

Improved efficiency as well as increased lifetime of turbines and compressors are important goals in turbomachinery development. A significant enhancement to accomplish these aims can be seen in online monitoring of the operating parameters of the machines. During the operation of compressors it is of high interest to predict critical events like flutter or stall which can be achieved by observing blade deformations and vibrations. We have developed a laser Doppler distance sensor (LDDS), which is capable of simultaneously measuring the radial blade expansions, the circumferential blade deflections as well as the circumferential velocities of the rotor blade tips. As a result, an increase of blade vibrations is measured before stall at characteristic frequencies. While the detected vibration frequencies and the vibration increase are in agreement with the measurement results of a commercial capacitive blade tip timing system, the measured values of the vibration amplitudes differ by a factor of three. This difference can be mainly attributed to the different measurement locations and to the different measurement approaches. Since the LDDS is applicable to metal as well as ceramic, carbon-fiber and glass-fiber reinforced composite blades, a universally applicable sensor system for stall prediction and status monitoring is presented.