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We demonstrate distributed measurement of the polarization beat length along single-mode optical fibers (SMFs) using slope-assisted Brillouin optical correlation-domain reflectometry (BOCDR) with high spatial resolution, long measurement range, high sampling rate, and single-end accessibility. The beat lengths of SMFs wound on mandrels with radii of 10.5, 7.5, and 3.4 cm are measured to be 36.0, 18.2, and 3.7 m, respectively, which agree well with theoretical calculations. This indicates that a unique beyond-nominal-resolution effect of slope-assisted BOCDR does not influence the measurement. Subsequently, distributed beat length measurement is demonstrated using an SMF comprising two sections wound on mandrels with different radii (10.5 and 3.4 cm).

A large, deep-seated ancient landslide was partially reactivated on 17 June 2020 close to the Aniangzhai village of Danba County in Sichuan Province of Southwest China. It was initiated by undercutting of the toe of this landslide resulting from increased discharge of the Xiaojinchuan River caused by the failure of a landslide dam, which had been created by the debris flow originating from the Meilong valley. As a result, 12 townships in the downstream area were endangered leading to the evacuation of more than 20000 people. This study investigated the Aniangzhai landslide area by optical and radar satellite remote sensing techniques. A horizontal displacement map produced using cross-correlation of high-resolution optical images from Planet shows a maximum horizontal motion of approximately 15 meters for the slope failure between the two acquisitions. The undercutting effects on the toe of the landslide are clearly revealed by exploiting optical data and field surveys, indicating the direct influence of the overflow from the landslide dam and water release from a nearby hydropower station on the toe erosion. Pre-disaster instability analysis using a stack of SAR data from Sentinel-1 between 2014 and 2020 suggests that the Aniangzhai landslide has long been active before the failure, with the largest annual LOS deformation rate more than 50 mm/yr. The 3-year wet period that followed a relative drought year in 2016 resulted in a 14% higher average velocity in 2018–2020, in comparison to the rate in 2014–2017. A detailed analysis of slope surface kinematics in different parts of the landslide indicates that temporal changes in precipitation are mainly correlated with kinematics of motion at the head part of the failure body, where an accelerated creep is observed since spring 2020 before the large failure. Overall, this study provides an example of how full exploitation of optical and radar satellite remote sensing data can be used for a comprehensive analysis of destabilization and reactivation of an ancient landslide in response to a complex cascading event chain in the transition zone between the Qinghai-Tibetan Plateau and the Sichuan Basin.

In this work we present a new method to optically obtain the convolution / correlation between two functions. The technique is based on obtaining higher powers of a properly designed phase-only hologram. The approach combines some of the advantages of the classical 4f and the JFTC correlator systems. These higher powers of the hologram transmission function can be obtained easily using a spatial light modulator (SLM) with an extended phase modulation of various cycles of 2π radians. SLMs with such extended phase modulation present useful unusual diffraction properties that can be exploited to surpass some limits of SLM technology. In this case we exploit them to obtain higher order optical correlation terms. Computational simulations and experimental results agree with theory.

Background: Due to lack of equipment for directly measuring crystal morphology, there has been little research on lenticular astigmatism. The purpose of this study was to accurately explore the correlation between internal astigmatism and lens astigmatism in patients with ametropia. Methods: This is a cross-sectional study conducted in the Affiliated Hospital of North Sichuan Medical College, China, in September 2020. Diopter values (refractive astigmatism, RA) of patients with ametropia was recorded, and the corneal and lens biological parameters were measured by CASIA2 (corneal/anterior segment optical correlation tomography analyzer). Biometric parameters, including the total corneal astigmatism (total corneal astigmatism, TCA), anterior and posterior curvature radius of the lens (anterior curvature radius of the lens, ACL; posterior curvature radius of the lens, PCL), internal astigmatism (internal astigmatism, IA), anterior and posterior astigmatism of the lens (anterior astigmatism of the lens, AAL; posterior astigmatism of the lens, PAL) were measured. Grouping and comparisons were made according to gender and age. Results: In total, 151 participants (293 eyes) were included in the analysis. There were significant ( PZ=-2.194, P=0.028) according to gender, but not in the other parameters. By age group, there were statistically significant differences in the TCA ( H=10.609, P=0.005), IA ( F=3.722, P=0.025), and PAL ( H=8.254, P=0.016), but not in the others. The IA was positively correlated with the age ( r=0.155, P=0.008), RA ( r=0. 534, Pr=0.308, Pr=-0.244, PY (IA) =-0.626 +0.447 X (AAL). Conclusions: Internal astigmatism is mainly related to the anterior astigmatism of the lens, and the higher the anterior astigmatism of the lens, the higher the internal astigmatism; At the same time, internal astigmatism increases with age.

We demonstrate the suppression of errors caused by the AM-FM phase delay of light source in the Brillouin optical correlation domain analysis. With an injection-locked DFB-LD the maximum error is suppressed by over 70 %.

Polarization imaging is a promising technology with great potential. Besides light intensity, it provides information in another dimension, polarization. When imaging through water, two frames of the target at two orthogonally polarized states, Imax and Imin, are needed. In most experiments, they are determined by searching for the darkest and brightest moments during polarizer rotation. But in cases where no noticeable difference can be observed, the final detection may fail. To cope with this problem, this study exploits optical correlation to assist to determine the optimal image pair. It provides reference information by comparing the similarity between two images and quantify it with parameter PCE (Peak-to-correlation energy). Final determination is based upon the fact that the optimal image pair should be in the least similarity. Experiments demonstrate that the location of optimal images can be accurately indicated through the method. Final recovery with the selected images presents the best contrast and image quality. The established strategy will enhance performance of underwater polarization imaging with better vision, higher resolution and accuracy.

Aeroelasticity is one of the biggest challenges in wind turbine rotor design, as the length of rotor blades increases which comes along with a slenderer design. The knowledge of the aeroelastic turbine behavior is of great importance. A comparison to field measurements is of huge importance when validating aeroelastic tools. However, the measurement of deformation and torsion in the field is not trivial and the conduction of realistic post-test simulations is a challenge. One crucial factor for these simulations is the wind field, which needs to be captured in a high spatial and temporal resolution. In this paper, the results of deformation measurements conducted in the field with an optical measurement method called Digital Image Correlation (DIC) on one rotor blade will be shown and compared to aeroelastic post-test simulations using highly resolved wind fields measured with a SpinnerLidar.

Semiconductor lasers are notoriously sensitive to optical feedback, and their dynamics and coherence can be significantly modified through optical reinjection. We concentrate on the dynamical properties of a very small (i.e., microscale) Vertical Cavity Surface Emitting Laser (VCSEL) operated in the low coherence region between the emission of (partially) coherent pulses and ending below the accepted macroscopic lasing threshold, with the double objectives of: 1) studying the feedback influence in a regime of very low energy consumption and 2) using the micro-VCSEL as a surrogate for nanolasers, where measurements can only be based on photon statistics. The experimental investigation is based on time traces and radiofrequency spectra (common for macroscale devices) and correlation functions (required at the nanoscale). Comparison of these results confirms the ability of correlation functions to satisfactorily characterize the action of feedback on the laser dynamics. Numerical predictions obtained from a previously developed, fully stochastic modeling technique provide very close agreement with the experimental observations, thus, supporting the possible extension of our observations to the nanoscale.

We show that 1 °C drift of laser temperature yields a strain error of ~8 με in Brillouin optical correlation-domain reflectometry. Under the assumption that the strain measurement accuracy is +/–20 με (severe requirement), +/–2.5 °C drift of the laser temperature can be permitted for proper system operation. We prove this prediction by performing distributed strain measurements at different laser temperatures. Our results indicate that, if we allow a strain measurement accuracy of approximately +/–100 με (or more), we can even remove the thermal control of the laser, leading to cost reduction and downsizing of the system.

We investigate the effect of the signal and receiver parameters on the performance of residual dispersion equalization for Nyquist optical time division multiplexing.

We represent the optical fiber output beam as linear superposition of orbital angular momentum (OAM) modes to quantify its purity. Through controlled experiments, we observe good agreement between the experimentally measured OAM and simulated spectrum.

Based on the “beyond-nominal-resolution” effect of slope-assisted Brillouin optical correlation-domain reflectometry, we demonstrate the detections of shortest-ever hot spots. A 2-mm-long strained section in a silica single-mode fiber and a 5-mm-long heated section in a plastic optical fiber are correctly detected in a distributed manner.

We proposed the signal processing based on machine learning in Brillouin optical correlation domain analysis/reflectometry (BOCDA/R). The methodology of the new idea is illustrated in this paper. The machine learning method is expected to perform more reliable and efficient than conventional methods.

An optical fibre-based strain sensor embroidered to a functionalised carbon structure (FCS) that can be used for structural health monitoring (SHM) is introduced. The aim of the design is not only to monitor strain, but also to act as a structural strengthening mechanism in the target application. The integration of optical fibres on the FCS is achieved by "interweaving" the two elements on a polymer textile infstrate in a grid formation using a specialised fabrication process. The thus obtained sensor was then characterised using a fibre optic Mach-Zehnder (MZ) interferometric setup where a variation in the fibre length, i.e. resulting from strain, would induce a variation in the interference pattern. To do so, two different functionalised skein samples (incorporating optical fibres) were infjected to varying elongation using a tensile testing machine by carefully incrementing the applied force. A good correlation between the applied force and measured length change was observed, showing the value of the dual-achievement of the proposed optical fibre-based mechanism in obtaining strain measurement while being utilised as a strengthening agent. © 2017 SPIE. BMBF/03ZZ0345

This paper presents the possibility of real-time measurement of the diameter of pectin particles during their jellification using an optical correlation method based on the spatial averaging of data.

This feature issue of Applied Optics contains a series of selected papers reflecting recent progress of correlation optics and illustrating current trends in vector singular optics, internal energy flows at light fields, optical science of materials, and new biomedical applications of lasers. (C) 2016 Optical Society of America

Based on the optical pulse correlation measurement and differential detection technique, an optical fibre sensor with high time resolution has been developed. However, due to the birefringence in single mode fibre induced by the uneven thermal effect, polarization fluctuation in the correlation signal was observed. In order to suppress the polarization fluctuation in the correlation sensing system, a polarization-suppressed optical correlation sensing system is proposed by utilizing the birefringence compensation approach in a retraced fibre path using Faraday rotator mirror elements. The polarization fluctuation of the output correlation signals is suppressed by more than 15 dB. The results of temperature experiment indicate that the linearity between the temperature and differential signal is further improved. With the reflection of the mirror, a double-pass monitoring is established, which significantly enhances the sensitivities of the sensing system to temperature and strain.

The optical properties based on Self-diffraction phenomena and the edge enhanced of optical correlation pattern effect with a Ca2+-doped (Ca0.28Ba0.72)0.75(Sr0.60Ba0.40)0.25Nb2O6 (CSBN75) crystals and a He-Ne laser at 632.8 nm are studied in this paper. The experimental results show that its practical application as photorefractive material is worth further investigation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We evaluate whether the measurement stability of Brillouin optical correlation-domain reflectometry (BOCDR) using plastic optical fibers (POFs) can be enhanced by polarization scrambling. Two major factors that affect the signal-to-noise ratio in BOCDR, i.e., the spatial resolution and the incident power are varied, and their influences on the distributed measurements with polarization scrambling are experimentally investigated. We thus clarify that in POF-based BOCDR, unlike BOCDR using standard silica glass fibers, polarization scrambling is effective in enhancing the measurement stability only when the spatial resolution is sufficiently low or when the incident power is sufficiently high.

A novel optical correlation domain reflectometry technique utilizing artificially-generated low-coherence light is proposed for long-range measurement with high resolution. We successfully demonstrate the selection of one correlation peak of a laser at an arbitrary delay for a fibre under test.

Injection molded polymer composite gears are being used in many power and or motion transmission applications. In order to widen the utilization of reinforced polymers for precision motion transmission and noise less applications, the accuracy of molded gears should be increased. Since the injection molded gear accuracy is significantly influenced by the material shrinkage behaviour, there is a need to understand the influence of fiber orientation and gate location on part shrinkage behaviour and hence the gear accuracy. Unreinforced and 20% short glass fiber reinforced Nylon 6/6 spur gears were injection molded in the laboratory and computer aided simulations of gear manufacturing was also carried out. Results of the mold flow simulation of gear manufacturing were correlated with the actual fiber orientation and measured major geometrical parameters of the molded gears. Actual orientation of the fibers near the tooth profile, weld line region and injection points of molded gears were observed using optical microscope and correlated with predicted fiber orientation. � Springer Science+Business Media B.V. 2006.

The use of optical cross correlations for characterizing timing jitter is investigated. Applications, limitations, and correspondence to radio frequency measurements are presented and clarified. The probability density function of the timing jitter of semiconductor mode-locked lasers is deconvolved from the cross-correlation measurements with the aid of pulse characterization techniques.

We have constructed an optical correlator for fast face recognition. Recognition rate can be markedly improved, if reference images are optically recorded and can be accessed directly without converting them to digital signals. In addition, a large capacity of optical storage allows us to increase the size of the reference database. We propose a new optical correlator that integrates the optical correlation technology used in our face recognition system and collinear holography. From preliminary correlation experiments using the collinear optical set-up, we achieved excellent performance of high correlation peaks and low error rates. We expect an optical correlation of 10 µs/frame, i.e., 100,000 face/s when applied to face recognition. This system can also be applied to various image searches.

The correlation between structural and electronic order–disorder effects in understanding the optical properties of flower-like ZnO nanocrystals synthesized by the microwave-assisted hydrothermal method at low temperatures and short times is discussed. Theoretical simulations were performed at the density functional theory level to gain a better understanding of the experimental data from X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), electron paramagnetic resonance (EPR), ultraviolet-visible diffuse reflectance (UV-vis) spectroscopy and photoluminescence (PL) measurement studies at different temperatures. The decrease in band gap values is due to the presence of intermediate states above the conduction band. These discrete levels are formed by structural and electronic disorder of tetrahedral [ZnO4] clusters which enhance the electron–hole pair.

We report full characterization of the intensity and phase of /spl sim/10-fs optical pulses using second-harmonic-generation frequency-resolved-optical-gating (SHG FROG). We summarize the subtleties in such measurements, compare these measurements with predicted pulse shapes, and describe the implications of these measurements for the creation of even shorter pulses. We also discuss the problem of validating these measurements. Previous measurements of such short pulses using techniques such as autocorrelation have been difficult to validate because at best incomplete information is obtained and internal self-consistency checks are lacking. FROG measurements of these pulses, in contrast, can be validated, for several reasons. First, the complete pulse-shape information provided by FROG allows significantly better comparison of experimental data with theoretical models than do measurements of the autocorrelation trace of a pulse. Second, there exist internal self-consistency checks in FROG that are not present in other pulse-measurement techniques. Indeed, we show how to correct a FROG trace with systematic error using one of these checks.

Bu çalışma, 28-30 Kasım 2013 tarihleri arasında Bursa[Türkiye]’da düzenlenen 8. International Conference on Electrical and Electronics Engineering (ELECO)’da bildiri olarak sunulmuştur. Optical ground wire (OPGW) is generally used to protect the phase conductors of the overhead power cables from high discharge currents due to lightning strikes and instantaneous current increase due to short-circuits or breakdowns as well as to provide data transmission for telecommunication purposes. OPGW cables are exposed to effects of environmental factors such as wind, rain, humidity and snow as well as cooling/heating effects of short-circuits and instantaneous current increases occurring on the phase conductor. When the OPGW cable is exposed to those effects, deformations occur on the cable insulation in time. In this study, using Raman effect based optical fiber distributed temperature sensing (DTS) method, temperature and thermal strain variations occurring along the OPGW cable due to environmental conditions, in particular wind speed and wind direction, have been analyzed and simulations have been performed. Furthermore, thermo-mechanical forces occurring on the OPGW cable have been expressed as a function of temperature change and Young modulus variations. Temperature and thermal strain dependencies of thermo-mechanical forces have also been derived. Using results of the theoretical analysis, simulations of thermo-mechanical force variations along the sensing fiber have also been performed considering the wind effect. The simulation model has been built up for central loose tube type OPGW cable containing single mode optical fiber operating at 1550 nm. For wind speed variations between 5.3 m/s and 10.3 m/s, minimum temperature detected on the cable varies between 26.86 degrees C and 22.41 degrees C, respectively, minimum thermal strain varies between 184 mu epsilon and 64.67 mu epsilon, respectively. Simulation results show that temperature sensitivities of thermo-mechanical forces are 26 times greater than thermal strain sensitivities. Chamber Elect Engineers Bursa Branch Istanbul Techn Univ, Fac Elect & Elect Engn Uludag Univ, Dept Elect & Elect Engn IEEE, Reg 8 IEEE Turkey Sect, CAS Chapter

International audience; The security of our recently proposed dual polarization encryption scheme of images isevaluated by numerical simulations. This consists of testing the resistance of the schemeagainst brute force, known-plaintext, chosen-plaintext and video sequence attacks. Whilesome attacks are ineffective (brute force, video sequence) others are effective(known-plaintext, chosen-plaintext), but only under certain assumptions. An optimization ofthe setup, which is based on a regular rotation of polarization optics angles (polarizers, waveplates), is proposed associating the use of a high dynamic range for the key image, or the useof a phase-only spatial light modulator in the target and in the key image channel. Thepossibility of the attacker decrypting an unknown image is thus strongly reduced. Theprecision required for optical specifications is also evaluated, in order to ensure a gooddecryption for an authorized user.

The combination of a computer generated target hologram and a large-area detector leverages optical correlation with a novel single-pixel spot/blur classifier to achieve low-power high-speed target detection with a wide field-of-view in room light.

A technique which increases the speed of automatic measurement of particles reconstructed from in-line holograms is presented. The reconstructed field is processed by simultaneous edge enhancement and correlation in an all-optical system. This allows the detection, localization and measurement of any particle corresponding to the filters introduced in the system. Experimental results are presented and discussed.

The dynamic distribution of the state of polarization (SOP) is studied theoretically and experimentally for aerial fibers with a finite polarization-mode dispersion (PMD). A dynamic mode coupling wave-plate model is proposed to describe the SOP correlation and account for the PMD variations. It is found that the model can closely describe the experimental dynamic correlation of the SOP for an aerial fiber. A new algorithm for PMD emulation is developed.

Optical trapping and manipulation have established a track record for cell handling in small volumes. However, this cell handling capability is often not simultaneously utilized in experiments using other methods for measuring single cell properties such as fluorescent labeling. Such methods often limit the trapping range because of high numerical aperture and imaging requirements. To circumvent these issues, we are developing a BioPhotonics Workstation platform that supports extension modules through a long working distance geometry. Furthermore, a long range axial manipulation range is achieved by the use of counter-propagating beam traps coupled with the long working distance. This geometry provides three dimensional and real time manipulation of a plurality of traps - currently 100 independently reconfigurable - facilitating precise control and a rapid response in all sorts of optical manipulation undertakings. We present ongoing research activities for constructing a compact next generation BioPhotonics Workstation.

We propose and experimentally demonstrate a novel method for extension of measurement range in a Brillouin optical correlation domain analysis (BOCDA) sensor system by cascading fibers with different Brillouin frequency shifts.

The problem of finding the function that maximizes the normalized output from a correlation filter is a classical problem in signal analysis. In this paper we solve this problem when the input is constrained to be real and positive.

“Fiber optic distributed sensing schemes” have been studied to make smart structures and materials. Using optical correlation domain techniques, we have realized mm-order spatial resolution, KHz-order measurement speed, and discriminative measurement of strain and temperature.

Error diffusion presents a very attractive method for manufacturing computer-generated holograms. However, it has certain defects that make it unsuitable for various optical processing applications, such as correlation. We present an extension of error diffusion which makes it suitable for the implementation of correlation filters.

This paper concerns mainly about two approaches to implement the anamorphic fractional correlation operation. Firstly, the definition of anamorphic fractional correlation is introduced. Secondly, an optical approach of implementing the correlation operation is presented. Lastly, since the optical implementation is somewhat troublesome, we will show how to exploit the anamorphic fractional correlation by computer-generated holography.

Using holographic matched filtering and electronic processing, small variations in surface displacement along the seam of a hermetic microcircuit package can be detected when the seam is stressed. Destructive analysis of a solder-sealed package reveals a strong correlation between optical signal variations and nonuniformity of solder adhesion and wetting along the seam. The technique promises potential application as a means of nondestructively inspecting for flaws in small welded or soldered seams.

Two optical correlation techniques for determining strain in materials are discussed. With the first method, strain is evaluated by measuring longitudinal variations in the separation between the object and the holographic filter. With the second method, a more direct determination of strain is made by simply measuring accurately the lateral displacement of two correlated areas. Experiments indicated that both methods have a sensitivity of about 10 ppm, with the potential of a slight further improvement.

Photorefractive polymers are dynamic holographic recording materials that allow for updating of images. They have been investigated over the last decade and have a wide range of applications including optical correlation, imaging through scattering media, and optical communication. Here, we review the achievement of the first updatable holographic 3D display based on photorefractive polymers and report the fabrication of a 6 x 6 inch 2 display, the largest photorefractive 3D display to date capable of recording and displaying new images every few minutes. The holograms can be viewed for several hours without the need for refreshing, and can be completely erased and updated whenever desired.

The express method of laser diagnostics of thrombus formation process in a whole blood is presented. This method is based on experimental investigations of backscattered laser radiation by a whole blood. The technique of experimental researches of backscattered laser radiation by whole blood is shown. It is established that the stochastization of fluctuations of backscattered intensity decreases under the influence of thrombin, that gives the possibility to estimate continuance of thrombus formation process.

We adapt concepts from matched filtering to propose a method for generating rapidly reconfigurable multiple beams. As a phase-only spatially filtering extension of the Generalized Phase Contrast (GPC) technique, the proposed method coined mGPC can yield dynamically reconfigurable optical beam arrays with high light efficiency for optical manipulation, high-speed sorting and other parallel spatial light applications [1].

A method based on cross-correlation is proposed for measurement and control of accurate delay variation between two ultra-short laser beams. The accuracy can reach to a few femtoseconds.

This paper describes a 1-D Focal Plane Processor incorporating 200 pixels for Continuous-Time Optical Correlation Applications. Each pixel incorporates a 2 mm times 10.9 mum photodiode whose current is scaled, at the pixel level, by 5 independent 3-bit programmable-gain current amplifiers. Correlation patterns, defined as 5 sets of 200 3-bits numbers, are communicated to the chip via a standard I2C interface. Correlation outputs are provided in current form through independent 8-bit-programmable amplifiers whose gains are also defined via I2C. The chip contains an alignment help by incorporating 3 rows of 100 conventional Active Pixel Sensors (APS) inserted at the top, middle, and lower part of the main photodiode array. The chip has been fabricated in a standard 0.35 mum CMOS technology and maximum power consumption is below 30 mW.

“Fiber optic nerve systems” have been studied to make structures and materials that can feel pain. We have developed the nerve systems with mm-order spatial resolution and kHz-order measurement speed, using optical correlation domain techniques.

The diffraction and interference of coherent light from lasers can be used to record and analyze metallographic structures. Optical transforms, holography, optical correlation, and other coherent light methods are presently being applied to materials problems ranging from basic research to testing and inspection. This paper describes the basic concepts used in some of these methods and describes examples of their application. Holography is a particularly attractive method for measuring changes in the shapes of objects, especially because it allows interferometric measurements without special surface preparation. The use of holography for studies of crystal growth and electropolishing is described in some detail, and reconstructed holograms are shown. Holography and other coherent light techniques can often reveal the presence of defects or inhomogeneities even when quantitative evaluation of the optical output is difficult.

We study the implementation of a correlation measurement technique for the characterization of squeezed light which is nearly free of electronic noise. With two different sources of squeezed light, we show that the sign of the covariance coefficient, revealed from the time resolved correlation data, is witnessing the presence of squeezing in the system. Furthermore, we estimate the degree of squeezing using the correlation method and compare it to the standard homodyne measurement scheme. We show that the role of electronic detector noise is minimized using the correlation approach as opposed to homodyning where it often becomes a crucial issue.