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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).

Zinc oxide clusters of different sizes and geometrical shapes have been synthesized and characterized experimentally and theoretically. The ZnO cluster models have been built and presented to study...

International audience; Observations of surface deformation within 1-2 km of a surface rupture contain invaluable information about the coseismic behavior of the shallow crust. We investigate the oblique strike-slip 2016 M7 Kumamoto, Japan, earthquake, which ruptured the Futagawa-Hinagu Fault. We solve for variable fault slip in an inversion of differential lidar topography, satellite optical image correlation, and Interferometric Synthetic Aperture Radar (InSAR)-derived surface displacements. The near-fault differential lidar pose several challenges. The model fault geometry must follow the surface trace at the sub-kilometer scale. Integration of displacement datasets with different sensitivities to the 3D deformation field and varying spatial distribution permits additional complexity in the inferred slip but introduces ambiguity that requires careful selection of the regularization. We infer a M w 7:09 þ0:03 −0:05 earthquake. The maximum slip of 6.9 m occurred at 4.5-km depth, suggesting an on-fault slip deficit in the upper several kilometers of the crust that likely reflects distributed and inelastic deformation within the shallow fault zone. Plain Language Summary Coseismic slip inversions quantify fault slip over a fault surface and serve as critical input into research on rupture propagation, earthquake triggering, and seismic hazard. However, coseismic slip distributions are rarely constrained by observations of surface displacement immediately adjacent to the fault rupture. This limits the quality of slip models within the shallowest crust. We solve for the slip field of the 2016 M7 Kumamoto, Japan, earthquake throughout the seismogenic crust using near-and far-field observations from differential lidar topography, satellite optical image correlation, and Interferometric Synthetic Aperture Radar surface displacements. The near-field differential lidar topography is critical for measuring shallow fault slip. We infer a M w 7:09 þ0:03 −0:05 earthquake and a maximum slip of 6.9 m at 4.5-km depth. This represents a shallow fault slip deficit where slip is greater at depth than at the surface. The missing shallow along-fault slip is accommodated as off-fault and inelastic deformation, presumably along secondary faults and folds in the shallow crust. Future earthquakes are also likely to be measured with different surface displacement data types. Researchers will have a new opportunity to learn about the behavior of the shallow fault zone and will also be presented with technical challenges such as those discussed here.

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.

We propose a novel approach for demodulating Brillouin Optical Correlation Domain Analysis (BOCDA) signals using digital dual-phase lock-in detection scheme, which enables simultaneous multi-point sensing.

We introduce the Raman amplification to increase the sensing range in the Brillouin optical correlation domain analysis (BOCDA). Compared to our previous report, the optimized Raman pumping scheme is numerically simulated and enhanced sensing length is experimentally demonstrated. The differential measurement method and time-domain data processing are further introduced in the backward distributed Raman pumped BOCDA system for the performance improvement. Strain changes of 1 mε over 7 cm have been measured at 52 km sensing fiber.

Azobenzene polymer based distributed ultraviolet sensor is characterized by Brillouin optical correlation domain analysis. Three types of UV sensor probes are made by coating the azobenzene polymer on bare fiber, acylated coated fiber and polyimide coated fiber. Brillouin frequency response by the UV exposure of each probe sensors are presented.

International audience

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 propose the distributed Raman amplification along the sensing fiber to enhance the measurement range of the Brillouin optical correlation domain analysis system to 50 km, where the time-domain data processing is adopted.

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 %.

Arabian journal of chemistry 14(3), 102992 (2021). doi:10.1016/j.arabjc.2021.102992, Published by Saudi Chemical Soc., Riyadh

Optical correlation measurements catch interference in coherent light from a Young’s double-slit interferometer system.

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.

Brillouin optical correlation-domain reflectometry (BOCDR) generally suffers from the trade-off relationship between the spatial resolution and the measurement range. In this work, we perform a proof-of-concept demonstration of a chirp modulation scheme to extend the measurement range of BOCDR. In this scheme, optical frequency is modulated using a chirp-shaped waveform. We show that, although the spatial resolution is slightly deteriorated, the measurement range and the range-to-resolution ratio can be relatively largely improved. In our preliminary experiment, the range-to-resolution ratio is 471, which is approximately 3 times higher than that of a standard configuration, proving the effectiveness of this scheme.

We present the state-of-the-art and future challenges of Brillouin optical correlation-domain reflectometry, which is the only fiber-optic distributed sensing technique that can simultaneously achieve single-end-access operation, high spatial resolution, random accessibility, and cost efficiency.

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.

In this paper, a novel method is proposed to optically verify the decoded images via single-shot imaging without reference wave using a binary intensity pattern. Optical imaging without reference wave is applied based on double random phase encoding (DRPE), and the recorded intensity pattern is further compressed, which contains only two quantization levels (i.e., 0 and 1). During the decoding, an iterative phase retrieval algorithm is developed and applied. It is demonstrated that decoded images do not visually render the input information due to the designed optical encoding strategy using only one binary intensity pattern, and optical verification is further conducted to effectively verify the decoded images. An additional security layer is established for the developed optical system, since optical verification is conducted based on optical encoding systems without direct observation of input information from the decoded images. It is the first to report the use of only one 1-bit intensity pattern in the DRPE system based on single-shot imaging without reference wave for secured verification via optical correlation.

International audience; We report findings on the optimization of the performances of correlation filters. First, we propound and validate an optimization of ROC curves adapted to correlation technique. Then, analysis suggests that a pre-processing of the input plane leads to a compromise between the robustness of the adapted filter and the discrimination of the inverse filter for face recognition applications. Rewardingly, our technical results demonstrate that this method is remarkably efficient to increase the performances of a VanderLugt correlator.

Quite a big boom has recently been experienced in the technology of unmanned aerial vehicles (UAV). In conjunction with optical correlation systems, it gives one a powerful tool for the creation of digital terrain models and orthophotomaps. This system was used for the documentation of landslides and inaccessible parts of the Nastup Tusimice mine in the North Bohemian Brown Coal Basin (CzechRepublic). The images were taken by the GATEWING X100 unmanned system that automatically scans an area of interest. For detailed documentation of selected parts of the mine, we used the method of digital terrestrial photogrammetry. The main objective was to find a suitable measurement technology for operational targeting of landslides and inaccessible parts of the mine, in order to prepare the basics for remediation work. Abstrakt Poměrně velký rozmach zaživa v posledni době technologie bezpilotnich leteckých prostředků (UAV). Ve spojeni s optickými korelacnimi systemy ziskame kvalitni nastroj pro tvorbu digitalniho modelu terenu a ortofotomapy. Uvedený system jsme použili pro dokumentaci sesuvných a nedostupných casti lomu v lokalitě Doly Nastup Tusimice v Severoceske hnědouhelne panvi (Ceska republika). Snimky byly pořizeny bezpilotnim systemem GATEWING X100, který automaticky nasnima zajmove uzemi. Pro podrobnou dokumentaci vybraných casti lomu jsme použili metodu digitalni pozemni fotogrammetrie. Hlavnim cilem měřeni bylo vytipovat vhodnou technologii pro operativni zaměřovani sesuvů a nedostupných casti lomu, za ucelem vyhotoveni podkladu pro sanacni prace.

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.

We present a polarization imaging method to image through highly turbid water based on the dependence of light scattering and the optical correlation theory. Experiments demonstrate its contribution to make “can’t see” into “can see”.

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.

This article is focused on new methods of image processing used in modern video surveillance systems. The aim of this article is usage of the latest knowledge in the field of digital signal processing (image and video) and optical correlation in the design and experimental verification of video surveillance system that should detect lost or abandoned luggage.

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

The modified Becke-Johnson exchange potential proposed by Tran and Blaha (TB-mBJ) is useful for accurate calculations of electronic band structures of solids. In this view, we used such potential together with spin–orbit coupling to calculate the electronic and optical correlation effects in bulk gold (Au) via first principle DFT. Inclusion of the relativistic effects in the simulation were found to play vital role on the optical properties of bulk Au. Furthermore, the imaginary part of the dielectric function of Au disclosed good agreement with the experimental results. Disclosure of good agreement between simulation and experimental results (up to Fermi level) was due to the improvement in the band structure of bulk Au achieved by incorporating spin–orbit coupling.

A method of all-optical correlation is proposed using the nonlinear phenomena Four Wave Mixing (FWM) of two different signals. The method shows a serial solution where correlation of an ultrafast real-time serialized broadband source is demonstrated using a Highly Non-Linear Fibre (HNLF) with correlation rate reaching 200MHz.

In this paper, We proposed a Optical Correlation for indoor positioning based LED-ID. The proposed Optical Correlation has a advantage to low-interference between spread code number sequences and LED-ID. it is applied a spread code to reduce the interference with additional information based LED-ID. The additional information is enable to detect in transmitted signal using auto correlation. Also we designed and implemented the Optical Correlation for clearly detecting the additional information. Simulations were performed to confirm the performance of BER and the power of additional information. Optical Correlation simulator to indoor positioning based LED-ID was implemented to prove a usefulness.

We introduce a novel concept for optical correlation spectroscopy of non-fluorescent absorbing nano-particles termed twin-focus photothermal correlation spectroscopy (Twin-PhoCS). This method exhibits a unique axial sensitivity, allowing for either the measurement of very slow axial dynamics or the determination of axial heterogeneities on sub-diffraction limited length-scales. To this end, the photothermal nano-lensing mechanism [Markus Selmke, Romy Schachoff, Marco Braun, and Frank Cichos, ACS Nano, 2012, 6(3), 2741] provides two sharply separated detection-subvolumes, comprising the twin-focus. The achieved axial sensitivity is superior to single detection-volume or dual-focus based fluorescence correlation spectroscopies. We demonstrate the sensitivity by measuring radiation-pressure induced flow velocities of diffusing 14 nm gold-colloids down to 10 nm ms−1 with the help of the provided analytical correlation functions.

Computer stereo vision makes heavy use of object distance detection. The primary method to detect object distance is to compare two images of the same scene taken from different vantage points. The necessity of comparing two images naturally leads us to investigate optical correlators.

Experimental investigations have been carried out to visualize bubble behavior and effect of gas flow rate and liquid concentration on bubble characteristics of Tetrafluoro ethane (R134a) in liquid R134a–Dimethyl Formamide (DMF) solution in a glass absorber. Bubble behavior was studied in still as well as flowing solution. At lower gas flow rates, bubbles tend to be spherical due to the dominance of surface tension. At higher gas flow rates, bubbles tend to be hemispherical due to the dominance of inertia force. Bubble diameter during detachment increases with increase in gas flow rates. Also, the bubble diameter initially increases as the solution concentration increases up to 0.075 kg kg −1 and then starts decreasing as the solution concentration increases further. At lower solution concentrations, effect of absorption driving potential ( x eq − x l ) is dominant than that of surface tension, due to this bubble diameter increases. When the solution concentration is increased further, effect of surface tension is dominant resulting in decrease in bubble diameter. Bubble diameter measured from the experiments is compared with that of the numerical model developed by the authors and other literature experimental correlations and it is found that the agreement is good. A correlation for bubble diameter during detachment is presented from the experimental studies, which can be useful for the design of R134a–DMF bubble absorber.

An optically addressed spatial light modulator (OASLM) records the image on a write beam and transfers it to a read beam. Some example application areas are: image transduction; optical correlation; adaptive optics; and optical neural networks. Current interest in OASLMs has been generated by the work of Qinetiq on 3D display. This work is based on Active tiling, where an image can be recorded in one part of the device and is memorised, whilst the remainder of the device is updated with images. This paper will explain this system and survey the technological alternatives for this application.

In the second part of this study, we compare both the wind speed and turbulence given by the Sodars with independent sets of measurements. In the case of the wind speed we compare the lowest Sodar data bin with a sonic anemometer located on a 7-m tower. The agreement between the two instruments was convincing with a regression slope near unity. The integrated turbulence measurements of the Sodars are compared with those obtained with a combined multi-aperture scintillation sensor and differential image motion monitor (MASS/DIMM) unit. It was found that the Sodars are indeed capable of quantitatively measuring optical turbulence, and agree with the MASS/DIMM measurements with a correlation coefficient of approximately 80% and a regression slope within 10% of unity. Additional acoustic noise in the Sodar data was identified using this comparison and removed from the data. © 2011 Springer Science+Business Media B.V.

Considering the practical application of target recognition with optoelectronic joint transform correlator,the infrared image detected was processed by multiwavelet transform,and its edge points were extracted by the method of local modulus maximum.Capturing much contour can improve the capacity of target recognition.The multiwavelet functions usually used to infrared target processing are GHM and SA4.Simulation experiments show that the correlation output of edges extracted by GHM is obviously better than that one of edges extracted by SA4,because the former edges carry much contour of image.Compared to the optical correlation detection result of original image with that of edge image extracted by GHM,it is found that the latter effectively enhances the intensity of correlation peaks.

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.

Distributed fiber-optic sensing based on Brillouin scattering has been extensively studied and many configurations have been developed so far. In this paper, we review the recent advances in Brillouin optical correlation-domain reflectometry (BOCDR), which is known as a unique technique with intrinsic single-end accessibility, high spatial resolution, and cost efficiency. We briefly discuss the advantages and disadvantages of BOCDR over other Brillouin-based distributed sensing techniques, and present the fundamental principle and properties of BOCDR with some special schemes for enhancing the performance. We also describe the recent development of a high-speed configuration of BOCDR (slope-assisted BOCDR), which offers a beyond-nominal-resolution detectability. The paper is summarized with some future prospects.

Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-27T11:24:46Z No. of bitstreams: 0 Made available in DSpace on 2014-05-27T11:24:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-08-18 This paper presents a comparative analysis between the experimental characterization and the numerical simulation results for a three-dimensional FCC photonic crystal (PhC) based on a self-assembly synthesis of monodispersive latex spheres. Specifically, experimental optical characterization, by means of reflectance measurements under variable angles over the lattice plane family [1,1, 1], are compared to theoretical calculations based on the Finite Di®erence Time Domain (FDTD) method, in order to investigate the correlation between theoretical predictions and experimental data. The goal is to highlight the influence of crystal defects on the achieved performance. Electrical Engineering Department EESC-USP University of Sao Paulo, Sao Carlos, SP Institute of Chemistry IQ-Unesp Sao Paulo State University, Araraquara, SP Institute of Chemistry IQ-Unesp Sao Paulo State University, Araraquara, SP

The useful application of optical pulse correlation sensor for wide region quasidistributed fiber strain measurement is investigated. Using region separation techniques of wavelength multiplexing with FBGs and time multiplexing with intensity partial reflectors, the sensor measures the correlations between reference pulses and monitoring pulses from several cascadable selected sensing regions. This novel sensing system can select the regions and obtain the distributed strain information in any desired sensing region.