A Modified Principal Component Analysis Method for Honeycomb Sandwich Panel Debonding Recognition Based on Distributed Optical Fiber Sensing Signals

The safety and integrity requirements of aerospace composite structures necessitate real-time health monitoring throughout their service life.To this end,distributed optical fiber sensors utilizing back Rayleigh scattering have been extensively deployed in structural health monitoring due to their advantages,such as lightweight and ease of embedding.However,identifying the precise location of damage from the optical fiber signals remains a critical challenge.In this paper,a novel approach which namely Modified Sliding Window Principal Component Analysis(MSWPCA)was proposed to facilitate automatic damage identification and localization via distributed optical fiber sensors.The proposed method is able to extract signal characteristics interfered by measurement noise to improve the accuracy of damage detection.Specifically,we applied the MSWPCA method to monitor and analyze the debonding propagation process in honeycomb sandwich panel structures.Our findings demonstrate that the training model exhibits high precision in detecting the location and size of honeycomb debonding,thereby facilitating reliable and efficient online assessment of the structural health state.

Investigating Optical Transport Network Performance:A Recurrence Plot Approach

In future optical transport networks,lightpath performance analysis is of great practical significance for fully automated management.In general,the quality of transmission(QoT)of lightpaths,measured by optical quality factor or optical signal-to-noise ratio,has a complex time-varying process,along with the interactions of the other lightpath state parameters(LSPs),such as transmit power,chromatic dispersion,polarization mode dispersion.Current studies are mostly focused on lightpath QoT estimation,but ignoring lightpath-level data analytics.In this case,our article proposes a novel lightpath performance analysis method considering recurrence plot(RP)and cross recurrence plot(CRP).Firstly,we give a detailed interpretation on the recurrence patterns of LSPs via a qualitative 2-D RP representation and its quantitative measure.It can potentially enable the accurate and fast lightpath failure detection with a low computational burden.On the other hand,CRP is devoted to modeling the relationships between lightpath QoT and LSPs,and the correlation degree is determined by a geometric mean of multiple indexes of cross recurrence quantification analysis.From the view of application,such CRP analysis can provide the effective knowledge sharing to guarantee more credible QoT prediction.Extensive experiments on a real-world optical network dataset have clearly demonstrated the effectiveness of our proposal.

Physics-informed deep learning for fringe pattern analysis

Recently,deep learning has yielded transformative success across optics and photonics,especially in optical metrology.Deep neural networks (DNNs) with a fully convolutional architecture (e.g.,U-Net and its derivatives) have been widely implemented in an end-to-end manner to accomplish various optical metrology tasks,such as fringe denoising,phase unwrapping,and fringe analysis.However,the task of training a DNN to accurately identify an image-to-image transform from massive input and output data pairs seems at best naive,as the physical laws governing the image formation or other domain expertise pertaining to the measurement have not yet been fully exploited in current deep learning practice.To this end,we introduce a physics-informed deep learning method for fringe pattern analysis (PI-FPA) to overcome this limit by integrating a lightweight DNN with a learning-enhanced Fourier transform profilometry (Le FTP) module.By parameterizing conventional phase retrieval methods,the Le FTP module embeds the prior knowledge in the network structure and the loss function to directly provide reliable phase results for new types of samples,while circumventing the requirement of collecting a large amount of high-quality data in supervised learning methods.Guided by the initial phase from Le FTP,the phase recovery ability of the lightweight DNN is enhanced to further improve the phase accuracy at a low computational cost compared with existing end-to-end networks.Experimental results demonstrate that PI-FPA enables more accurate and computationally efficient single-shot phase retrieval,exhibiting its excellent generalization to various unseen objects during training.The proposed PI-FPA presents that challenging issues in optical metrology can be potentially overcome through the synergy of physics-priors-based traditional tools and data-driven learning approaches,opening new avenues to achieve fast and accurate single-shot 3D imaging.

Evaluation of visual quality of spherical and aspherical intraocular lenses by Optical Quality Analysis System

AIM： To evaluate the impact of spherical and aspherical intraocular lenses on the postoperative visual quality of age-related cataract patients using Optical Quality Analysis System （OQAS）. METHODS： Seventy-four eyes with age-related cataracts were randomly divided into spherical and aspherical lens implantation groups. Best-corrected visual acuity （BCVA） was measured preoperatively, one day, one week, two weeks, one month and two months after surgery. A biometric systems analysis using the OQAS objective scattering index （OSI） was performed. RESULTS： There were no significant differences in visual acuity （P〉0.05） before and after spherical and aspheric lens implantation. There was a negative linear correction between the OSI value and BCVA （t-=-0.634, P=-0.000）, and positive corrections between the OSI value and the lens LOCUS III value of nucleus color （NC）, nucleus opacity （NO）, cortex （C） and posterior lens capsular （P） （r=0.704, P=0.000; r=0.514, P=0.000; r=0.276, P=0.020; r=0.417, P=-0.000, respectively）. OSI values of spherical vs aspherical lenses were 11.5±3.6 vs 11.8±3.4, 4.1±0.9 vs 3.3±0.8, 3.5±0.9 vs 2.7±0.7, 3.3±0.8 vs 2.6±0.7, 3.2±0.7 vs 2.5±0.8, and 3.2±0.8 vs 2.50.8 before and ld, 1, 2wk, 1 and 2mo after surgery, respectively. All time points varied significantly （P〈0.01） between the two groups. CONCLUSION： Aspherical IOLs does not significantly affect visual acuity compared with spherical IOLs. The OSI value, was significantly lower in the aspherical lens group compared with the spherical lens. This study shows that objective visual quality of aspheric IOLs is better than that of the spherical lens by means of OQAS biological measurement method.

Brillouin optical time-domain analysis for geotechnical monitoring

In this paper, we show some recent experimental applications of Brillouin optical time-domain analysis （BOTDA） based sensors for geotechnical monitoring. In particular, how these sensors can be applied to detecting early movements of soil slopes by the direct embedding of suitable fiber cables in the ground is presented. Furthermore, the same technology can be used to realize innovative inclinometers, as well as smart foundation anchors.

Optical coherence tomography assessed retinal nerve fiber layer thickness in patients with Alzheimer's disease:a meta-analysis

AIM:To investigate the difference of retinal nerve fiber layer(RNFL) thickness between Alzheimer's disease patients and normal people,so as to provide clue for the early diagnosis of Alzheimer's disease.· METHODS:The articles on the association of RNFL thickness and Alzheimer's disease were retrieved by searching international and national databases.The qualified articles were assessed by meta analysis with Stata11.0 software.The results were pooled using weighted mean difference(WMD) with a corresponding 95% confidence interval(CI).· RESULTS:Totally 7 studies enrolled 324 eyes were included in the meta-analysis.The results of meta analysis showed that in AD patients,there was a significant average RNFL thickness reduction compared with the control group [WMD=-17.561,95%CI:(-23.971,-11.151)].There were significant differences in superior,inferior,nasal and temporal RNFL thickness between the two groups.WMD with a 95%CI were [-18.829,95%CI:(-25.915,-11.743);P<0.05],[-25.775,95%CI:(-34.304,-17.247);P <0.05],[-16.877,95%CI:(-29.141,-4.613);P<0.001] and [-14.565,95%CI:(-28.002,-1.128);P<0.001] respectively.Begg's test and Egger's test did not show significant difference,funnel plot was basically symmetrical,indicating that there was no publication bias existed.· CONCLUSION:There are significant differences in the RNFL thickness in all quadrants between the two groups.RNFL thickness is reduced in AD patients compared with the control group.·

Mechanical analysis of C/C composite grids in ion optical system

The ion thruster is an engine with high specific impulse for satellites and spacecrafts,which uses electric energy to boost the spacecraft.The ion optical system,also known as gate assemblies which consist of acceleration and screen grids,is the key component of the ion thruster.In this paper,the static mechanical properties of the C/C composite grids are evaluated based on the structural design.Representative volume element (RVE) is adopted to simplify the braded composite structure as a continuum material.The dynamical behavior of the 100 mm ion thruster optics in the launch environment (1000g shock-load) is numerically modeled and simulated with the half-sine pulse method.The impact response of the C/C and molybdenum gate assemblies on the stress distribution and deformation is investigated.The simulated results indicate that the magnitudes of the normal displacement of the composite grids subject to the uniformly distributed load are on the same level as molybdenum grids although the normal stiffness of the composite grids is much smaller.When subject to impact loading,the stress distribution in the C/C composite grids is similar to molybdenum grids while the stress magnitude is much smaller.This finding shows that the C/C gate assemblies outperform molybdenum grids and meet the requirement of long lifetime service in space travel.

Theoretical Analysis of Retrieving Atmospheric Columnar Mie Optical Depth from Downward Total Solar Radiative Flux

In this paper, the principle to determine the atmospheric columnar Mie optical depth from downward total solar radiative flux is theoretically studied, and the effect on Mie optical depth solution of the errors in surface albedo, sin-gle scattering albedo, asymmetrical factor of scattering phase function, instrumental constant and the approximate expression of diffusion flux is analy/ed, and then a method for determining surface albedo in shorter wavelength range is presented.

Structural and optical analysis of Cr_2N thin films prepared by DC magnetron sputtering

Chromium nitride （Cr2N） thin films were prepared by a DC magnetron sputtering technique. The deposition temperature was raised from 50 to 300℃, and its influence on the film structure and refractive index was investigated. X-ray diffraction analysis shows that the crystalline strucure of the films transforms from the （101） to （002） oriented hexagonal CrzN phase as the increase of substrate tempera- ture above 50℃, and a highly texatred film grows at 100℃. An empirical relation between the crystalline orientation and infrared active modes of the films is obtained, i.e., the Fourier transform infrared （FTIR） spectrum of the film prepared at 50℃ exhibits only A1 （TO） mode. The prominent peak in the FTIR spectra of the film prepared above 50℃is assigned to the E1 （TO） mode and is correlated with the （002） or c-axis oriented hexagonal wurtzite phase of Cr2N. In the surface analysis of atomic force microscopy, a transformation from the featureless surface to columnar-type morphology is observed with the increase of substrate temperature from 50 to 100℃, exhibiting c-axis oriented crystallite growth. A further increase in substrate temperature to 200℃ causes the c-axis crystallites to merge, resulting in the formation of voids. The refractive index （n） of the deposited films is obtained using spectroscopic ellipsometry.

Analysis of the blackbody-radiation shift in an ytterbium optical lattice clock

We accurately evaluate the blackbody-radiation shift in a171 Yb optical lattice clock by utilizing temperature measurement and numerical simulation. In this work. three main radiation sources are considered for the blackbody-radiation shift, including the heated atomic oven, the warm vacuum chamber, and the room-temperature vacuum windows. The temperatures on the outer surface of the vacuum chamber are measured during the clock operation period by utilizing seven calibrated temperature sensors. Then we infer the temperature distribution inside the vacuum chamber by numerical simulation according to the measured temperatures. Furthermore, we simulate the temperature variation around the cold atoms while the environmental temperature is fluctuating. Finally, we obtain that the total blackbody-radiation shift is -1.289（7）Hz with an uncertainty of 1.25×10;for our;Yb optical lattice clock. The presented method is quite suitable for accurately evaluating the blackbody-radiation shift of the optical lattice clock in the case of lacking the sensors inside the vacuum chamber.

Vascular Stress Analysis Based on in vivo Intravascular Optical Coherence Tomography Image Segmentation

Identification of carotid artery atherosclerosis is crucial for the diagnosis of the cerebral apoplexy and other vascular diseases.Intravascular optical tomography(IVOCT)has been employed to clinical coronary imaging for several years.Vessel morphological information on IVOCT images together with blood flow information on Doppler OCT(DOCT)images could provide a more accurate internal environment of arteries.Images integrated with fluid-structure interaction(FSI)could obtain the accurate mechanical responses and the quantitative material characters.A porcine carotid artery was imaged with an intravascular system(C7-XR,St.Jude Medical Inc.St.Paul,Minnesota,USA)in vivo,during which 120 images of one section and 600 images of a 5 mm/s pull back were captured within 6 s.Those images were then overlapped with Doppler phase changes to imply the changes in flow profiles.Segmentation and quantification of vessel structure was done in the software(MATLAB 2014b),including specifically the segmentation of lumen,imaging catheter,vessel wall and the guide wire.Appropriate interpolation functions are selected in the coordinate transformation algorithm to have smooth boundaries from images.A set of flow algorithms include image segmentation,three-dimensional/two-dimensional model reconstruction,inversion of material parameters,fitting of experimental velocity data and theoretical derivation based on simulation results is proposed.All steps are programmed to provide a theoretical basis for the future simplified process control.3D-reconstruction FSI model was built in SOLIDWORKS by lofting operation based on the segmentation results.Commercial finite element software(COMSOL 5.3,Sweden)numerically analyzed the entity model to obtain vessel stress/strain and flow shear stress data.Boundary conditions are from the OCT detection.Material of the artery was set to be the modified Mooney-Rivlin constitutive model and the parameters used were adjusted in an algorithm to match an ex vivo experiment.Wall shear stresses(WSS)and vessel deformations were chosen to measure the conditions of the artery and would serve as a target variables for future prediction.Thus,the geometric information together with the data of materials and other mechanical properties are possible to obtain during the imaging process.Segmentation process provided anatomically correct models of a two-layered artery.Numerical simulation permits reliable stress distribution in which the position of catheter and the artery curvature have a neglectable disturbance.Shear stress of the fluid is quite small compared with that of the wall at the same interface,which shows good agreement with the former studies.Moreover,a high flushing speed of 0.1 mps have little impact on the stress distributions and magnitudes,which denotes that the OCT imaging process brings little harm to the vessel.It is the first attempt to combine the OCT imaging and Doppler OCT within a full algorithm and a structural analysis.This study is helpful for the biomechanical property studies of carotid arteries and the development of medical imaging technology.

Application of Optical Flow Analysis to Shadowgraph Images of Impinging Jet

In this study, we apply the optical flow method to the time-series shadowgraph images of impinging jets using a high-speed video camera with high spatial and temporal resolution. This image analysis provides quantitative velocity vector fields in the object space without tracer particles. The analysis results clearly capture the details of the coherent vortex structure and its advection from the shear layer of the free jet. Although the results still leave challenges for the quantitative validation, the results show that this analysis method is effective for understanding the details of the physical phenomenon based on the quantitative values extracted from the shadowgraph images.

Quantitative analysis of early diabetic retinopathy based on optical coherence tomography angiography biological image

BACKGROUND With the development of the economy and improvements in living standards,the incidences of diabetes mellitus(DM)and diabetic retinopathy(DR),which is a complication of DM,are on the rise.AIM To analyze early DR in patients with macular zone changes in biological images using optical coherence tomography angiography METHODS A prospective case study was performed on 59 participants:35 healthy eyes(control group),35 eyes with diabetes but no DR group(no DR group),and 35 eyes with mild DR(NPDR group).All quantitative comparisons of parameters,including the fovea vascularity area,circularity index,and vascular complexity parameters,were performed using a biological image analysis software.RESULTS The foveal avascular zone(FAZ)area,FAZ circularity index,number of branches in the area,and the total of the single branches’length in the area was 0.366±0.031,0.834±0.037,3241.8±268.3,and 3.860×107±0.194×107,and 0.421±0.030,0.739±0.023,2956.6±476.4,and 3.177×107±0.161×107 in the no DR group and the NPDR group,respectively,which were significantly different from the corresponding parameters of the control group(P<0.05).Moreover,there were significant differences between these two groups(P<0.05).CONCLUSION This study shows that early microcirculation changes in the macular area of the retina is associated with disease progression.Early changes in DR can be analyzed using optical coherence tomography angiography.

Trend Analysis of Aerosol Optical Depth and &#197ngstr&#246m Exponent Anomaly over East Africa

Trend analysis of atmospheric aerosols enhances confidence in the evaluation of both direct and indirect effects of aerosols on regional climate change. To comprehensively achieve this over East Africa, it’s important to understand aerosols temporal characteristics over well selected sites namely Nairobi (1°S, 36°E), Mbita (0°S, 34°E), Mau Forest (0.0°S - 0.6°S;35.1°E - 35.7°E), Malindi (2°S, 40°E), Mount Kilimanjaro (3°S, 37°E) and Kampala (0°N, 32.1°E). In this context, trend analysis (annual (in Aerosol Optical Depth (AOD) at 550 nm and &#197ngstr&#246m Exponent Anomaly (&#197EA) at 470 - 660 nm) and seasonal (AOD)) from Moderate Resolution Imaging Spectroradiometer (MODIS) were performed following the weighted least squares (WLS) fitting method for the period 2000 to 2013. The MODIS AOD annual trends were ground-truthed by AErosol RObotic NETwork (AERONET) data. Tropical Rainfall Measurement Mission (TRMM) was utilized to derive rainfall rates (RR) in order to assess its influence on the observed aerosol temporal characteristics. The derived annual AOD trends utilizing MODIS and AERONET data were consistent with each other. However, monthly AOD and RR were found to be negatively correlated over Nairobi, Mbita, Mau forest complex and Malindi. There was no clear relationship between the two trends over Kampala and Mount Kilimanjaro, which may imply the role of aerosols in cloud modulation and hence RR received. Seasonality is evident between AOD and &#197EA annual trends as these quantities were observed to be modulated by RR. AOD was observed to decrease over East Africa except Nairobi during the study period as a result of RR during the study period. Unlike the other study sites, Nairobi shows positive trends in AOD that may be attributed to increasing populace and fossil fuel, vehicular-industrial emission and biomass and refuse burning during the study period. Negative trends over the rest of the study sites were associated to rain washout. The AOD and &#197EA derived annual trends were found to meet the statistical significance of 95% confidence level over each study site.

AFM Analysis on Polymer Optical Micro-Resonators: Investigation on Quality Factor Origin

This paper deals with the surface analysis of spherical polymeric optical micro-resonators in order to correlate surface defects with optical characteristics. Atomic force microscopy was used on structures to determine surface quality, which is the main origin of optical scattering losses. Surface morphologies were numerically treated to enable a relevant investigation on surface parameters such as root mean square (RMS) roughness (30.1 +/- 3.0 nm) or correlation length (few microns) necessary to express optical quality factors. A statistical analysis was conducted for calibration of these parameters as a function of cavities’ diameter. Results are in perfect agreement with spectral analyses performed in parallel on others structures. This comparison highlights the main role of scattering losses on quality factor origin.

Analysis of Mechanical Behavior of Composite Tissues Using Vibrational Optical Coherence Tomography

Extracellular matrices (ECMs) found in vertebrate tissues are fiber reinforced composite materials that prevent premature mechanical failure, store, transmit, and dissipate mechanical energy generated by the musculoskeletal system. We have developed a new method using optical cohesion tomography and vibrational analysis to non-destructively and non-invasively measure the mechanical properties of composite tissues and polymeric materials. In addition, this method can be used to measure the moduli of individual components of composite materials and perform “mechanical spectroscopy” on materials. In addition, we propose that measurement of the resonant frequency of a material minimizes the viscoelastic behavior of a composite material. This approach simplifies the analysis of mechanical behavior of polymers and others materials that demonstrate time-dependence to their properties.

Beam Steering Analysis in Optically Phased Vertical Cavity Surface Emitting Laser Array

Beam steering in implant defined coherently coupled vertical cavity surface emitting laser （VCSEL） arrays is simulated using the FDTD solution software. Angular deflection dependent on relative phase differences among elements, inter-element spacing, element size and emitted wavelength is analyzed detailedly and systematically. We design and fabricate 1×2 implant defined VCSEL arrays for optimum beam steering performance. Electroni- cally controlled beam steering with a maximum deflection angle of 1.6° is successfully achieved in the 1 × 2 VCSEL arrays. The percentage of the power in the central lobe is above 39% when steering. The results show that the steering is controllable. Compared with other beam steering methods, the fabrication process is simple and of low cost.

Rapid online analysis of trace elements in steel using a mobile fiber-optic laser-induced breakdown spectroscopy system

A mobile fiber-optic laser-induced breakdown spectrometer(FO-LIBS) prototype was developed to rapidly detect a large quantity of steel material online and quantitatively analyze the trace elements in a large-diameter steel tube.Twenty-four standard samples and a polynomial fitting method were used to establish calibration curve models.The R^2 factors of the calibration curves were all above 0.99,except for Cu,indicating the elements’ strong self-absorption effect.Five special steel materials were rapidly detected in the steel mill.The average absolute errors of Mn,Cr,Ni,V,Cu,and Mo in the special steel materials were 0.039,0.440,0.033,0.057,0.003,and0.07 wt%,respectively,and their average relative errors fluctuated from 2.9% to 15.7%.The results demonstrated that the performance of this mobile FO-LIBS prototype can be compared with that of most conventional LIBS systems,but the more robust and flexible characteristics of the FO-LIBS prototype provide a feasible approach for promoting LIBS from the laboratory to the industry.

Machine Learning-Based Alarms Classification and Correlation in an SDH/WDM Optical Network to Improve Network Maintenance

The evolution of telecommunications has allowed the development of broadband services based mainly on fiber optic backbone networks. The operation and maintenance of these optical networks is made possible by using supervision platforms that generate alarms that can be archived in the form of log files. But analyzing the alarms in the log files is a laborious and difficult task for the engineers who need a degree of expertise. Identifying failures and their root cause can be time consuming and impact the quality of service, network availability and service level agreements signed between the operator and its customers. Therefore, it is more than important to study the different possibilities of alarms classification and to use machine learning algorithms for alarms correlation in order to quickly determine the root causes of problems faster. We conducted a research case study on one of the operators in Cameroon who held an optical backbone based on SDH and WDM technologies with data collected from 2016-03-28 to “2022-09-01” with 7201 rows and 18. In this paper, we will classify alarms according to different criteria and use 02 unsupervised learning algorithms namely the K-Means algorithm and the DBSCAN to establish correlations between alarms in order to identify root causes of problems and reduce the time to troubleshoot. To achieve this objective, log files were exploited in order to obtain the root causes of the alarms, and then K-Means algorithm and the DBSCAN were used firstly to evaluate their performance and their capability to identify the root cause of alarms in optical network.