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Pattern recognition of optical label is utilized not only in packet switches but also in the field of data security due to its wide range of applications. In particular, pattern recognition using waveguide devices is highly valued because it eliminates the need for encoder processing. However, existing methods suffer from the problem of degraded contrast ratio because half of the input power are emitted from non‐target waveguides. In this article, a method is proposed to improve the contrast ratio employing a 4×$\times$4 multi‐mode interference (MMI) coupler with multiple input signals. The theoretical results reveal that the proposed method improves the contrast ratio from 3.0 dB to 9.5 dB and ∞$\infty$ dB for the three‐input and four‐input cases, respectively, for quadrature phase‐shift keying (QPSK)‐modulated signal. Furthermore, numerical simulation was performed through the three dimension finite‐difference time‐domain (3D‐FDTD) method, and the proposed scheme successfully discriminated each QPSK pattern. The power value |E|2$|E|^2$ at all ports closely matches the theoretical value, and the ratios of 9.5 dB and >$>$30.0 dB are numerically obtained. [ABSTRACT FROM AUTHOR]

Abstract Pattern recognition of optical label is utilized not only in packet switches but also in the field of data security due to its wide range of applications. In particular, pattern recognition using waveguide devices is highly valued because it eliminates the need for encoder processing. However, existing methods suffer from the problem of degraded contrast ratio because half of the input power are emitted from non‐target waveguides. In this article, a method is proposed to improve the contrast ratio employing a 4×4 multi‐mode interference (MMI) coupler with multiple input signals. The theoretical results reveal that the proposed method improves the contrast ratio from 3.0 dB to 9.5 dB and ∞ dB for the three‐input and four‐input cases, respectively, for quadrature phase‐shift keying (QPSK)‐modulated signal. Furthermore, numerical simulation was performed through the three dimension finite‐difference time‐domain (3D‐FDTD) method, and the proposed scheme successfully discriminated each QPSK pattern. The power value |E|2 at all ports closely matches the theoretical value, and the ratios of 9.5 dB and >30.0 dB are numerically obtained.

Present paper proposes the design of an Optical Test Bench (OTB) for an N-bit optical multiplier, optical convolution, and optical correlation circuit. OTB is constructed from a silicon-based optical microring resonator (OMRR). The OTB functions as an optical 4:3 counter, 2 × 2 optical multiplier, and 2 × 2 optical partial product generator circuit. OTB has been designed to be capable of designing any order of optical multiplier, optical convolution, and optical correlation circuit. OTB has been optimized with a small ring radius of 3.546 um and a low power of 1.19 mW. The transfer function of the OTB has been developed in Z-domain. The pole-zero plot is used to validate OMRR optical switching in the frequency domain. The optical switching of the designed OTB has been validated using various critical features such as extinction ratio, contrast ratio with respect to ring radius, and coefficient of coupling to predict the circuit's correctness and feasibility. All the analyses were successfully carried out in a MATLAB environment. [ABSTRACT FROM AUTHOR]

In the Pulfrich illusion, the depth of a moving object is misperceived due to induced retinal disparity and/or interocular velocity differences arising from differences in luminance, contrast, or spatial frequency between the two eyes. These effects have been shown to occur both for visual deficits and for optical corrections that introduce significant binocular differences between the retinal images. However, it remains unknown to what extent the illusion might arise given normal variation between the eyes, such as natural interocular variation in pupil diameter (anisocoria). To assess this, we examined the threshold interocular retinal illuminance difference required to experience illusory depth in two random-dot fields moving in opposite directions in 24 normally-sighted observers with dilated pupils. Interocular difference in retinal illuminance was induced by placing neutral density filters of different intensities before the left eye. A minority of subjects (n = 8) did not provide meaningful data on changes in the experience of illusory depth with interocular difference in retinal illuminance and four subjects showed biases >±10% from the 50% point of subjective equality in the psychometric function. For the remaining 12 participants, the retinal illuminance had to differ by approximately 40% for the depth between the planes to become visible at threshold levels. This difference was approximately constant over a range of absolute luminance levels from 10 to 80 cd/m2. Our results suggest that while motion-in-depth illusions due to interocular differences in retinal illuminance may be pronounced in certain ophthalmic diseases or following certain optical interventions, it is unlikely to be manifest as a result of normal interocular variations in retinal illuminance. Further, our results also point towards the existence of substantial individual differences in the experience of what is otherwise thought of as a readily appreciable motion-in-depth illusion. [ABSTRACT FROM AUTHOR]

Since Gerchberg-Saxton algorithm was developed, it has been applied in various fields, e.g., optical display and optical tweezers. In this paper, three-dimensional (3D) Gerchberg-Saxton optical correlation is proposed. A 2D image is divided into particle-like points placed in 3D space, which are simultaneously encoded into the cascaded phase masks by using a modified Gerchberg-Saxton algorithm. The extracted phase masks can be flexibly compressed, and the decoded images can be verified via optical correlation. It is also illustrated that high security and high flexibility can be achieved by using the proposed 3D Gerchberg-Saxton correlation method. The proposed 3D Gerchberg-Saxton algorithm can provide a new and significant insight on optical correlation.

Our understanding of pull-apart basins and their fault systems has been enhanced by analog experiments and simulations. However, there has been scarce interest to compare the faults that bound pull-apart basins with surface ruptures during earthquakes. In this study, we investigated the effects of a 2018 earthquake (Mw 7.5) on a pull-apart basin in the Palu–Koro fault system, Sulawesi Island, Indonesia, using geomorphic observations on digital elevation models and optical correlation with pre- and post-earthquake satellite images. A comparison of active fault traces determined by geomorphology with the locations of surface ruptures from the 2018 earthquake shows that some of the boundary faults of the basin are inactive and that active faulting has shifted to basin-shortcut faults and relay ramps. We also report evidence of lateral spreading, in which alluvial fan materials moved around the end of the alluvial fan. These phenomena may provide insights for anticipating the location of future surface ruptures in pull-apart basins.

With the development of synthetic aperture radar (SAR), it is more and more important to recognise the image obtained by SAR. SAR is a useful tool for geoscience and remote sensing, and there are a large amount of SAR images and products. How to quickly identify and process this massive information in the shortest time and find the target in time is the focus of research in this field. In the traditional processing method, the digital processing is used. It is time and storage consumption due to its massive data. This study proposes optical methods for target recognisation of SAR images. In this method, it takes the advantages of high speed and high resolution in optical processing methods to solve the bottleneck encountered by traditional methods. The method is based on an optical correlator. The optical processing method has a large capacity for a single processing and has a great advantage over the simple calculation method in processing speed. The experimental results demonstrate the effectiveness of the optical processing method.

With the development of synthetic aperture radar (SAR), it is more and more important to recognise the image obtained by SAR. SAR is a useful tool for geoscience and remote sensing, and there are a large amount of SAR images and products. How to quickly identify and process this massive information in the shortest time and find the target in time is the focus of research in this field. In the traditional processing method, the digital processing is used. It is time and storage consumption due to its massive data. This study proposes optical methods for target recognisation of SAR images. In this method, it takes the advantages of high speed and high resolution in optical processing methods to solve the bottleneck encountered by traditional methods. The method is based on an optical correlator. The optical processing method has a large capacity for a single processing and has a great advantage over the simple calculation method in processing speed. The experimental results demonstrate the effectiveness of the optical processing method. [ABSTRACT FROM AUTHOR]

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 Mw7.09−0.05+0.03 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 Mw7.09−0.05+0.03 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. Key Points: We conduct an earthquake slip inversion using differential lidar topography, optical image correlation, and InSAR imageryWe show how each data set constrains the variable fault slipThe apparent shallow slip deficit may reflect shallow off‐fault deformation [ABSTRACT FROM AUTHOR]

Brillouin optical correlation-domain technologies are reviewed as "fiber optic nerve systems" for the health monitoring of large structures such as buildings, bridges, and aircraft bodies. The Brillouin scattering property is used as a sensing mechanism for strain and/or temperature. Continuous lightwaves are used in the technologies, and their optical coherence properties are synthesized to realize position-selective measurement. This coherence manipulation technology is called the "synthesis of optical coherence function (SOCF)". By utilizing SOCF technologies, stimulated Brillouin scattering is generated position-selectively along the fiber, which is named "Brillouin optical correlation domain analysis (BOCDA)". Spontaneous Brillouin scattering, which takes place at any portion along the fiber, can also be measured position-selectively by the SOCF technology. This is called "Brillouin optical correlation domain reflectometry (BOCDR)". When we use pulsed lightwaves that have the position information, sensing performances, such as the spatial resolution, are inherently restricted due to the Brillouin scattering nature. However, in the correlation-domain technologies, such difficulties can be reduced. Superior performances have been demonstrated as distribution-sensing mechanisms, such as a 1.6-mm high spatial resolution, a fast measurement speed of 5000 points/s, and a 7000-με strain dynamic range, individually. The total performance of the technologies is also discussed in this paper. A significant feature of the technologies is their random accessibility to discrete multiple points that are selected arbitrarily along the fiber, which is not realized by the time domain pulsed-lightwave technologies. Discriminative and distributed strain/temperature measurements have also been realized using both the BOCDA technology and Brillouin dynamic grating (BDG) phenomenon, which are associated with the stimulated Brillouin scattering process. In this paper, the principles, functions, and applications of the SOCF, BOCDA, BOCDR, and BDG-BOCDA systems are reviewed, and their historical aspects are also discussed. [ABSTRACT FROM AUTHOR]

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.

In light of the growing body of research that is revealing the significant role of the auditory domain in sport, the present study aims to investigate the contribution of early auditory and visual information to the prediction of volleyball serves’ length. To this purpose, three within-subjects experiments were run, which differed among them in terms of stimuli (audiovisual congruent vs audiovisual incongruent; audio only vs video only) and/or in terms of number of possible answers. In particular, expert volleyball players were asked to predict the length of temporally occluded overhand serves, choosing among either two or three possible landing sectors. Response accuracy and response times were measured. For the incongruent stimuli, the results revealed that the percentage of predictions in line with early auditory information was significantly higher than the respective percentage of predictions in line with early visual information. For unimodal stimuli, prediction accuracy was significantly higher on the basis of auditory information than on the basis of visual information, without any difference on response times. Taken together, the results highlighted the relevance of early auditory information for the prediction of volleyball serves’ length. [ABSTRACT FROM AUTHOR]

In this paper, hierarchically optical double-image correlation is proposed by using 3D phase retrieval algorithm with a series of random function orders in fractional Fourier transform domain. At each hierarchical level, two grayscale input images are divided into particle-like points placed in 3D space, which are encoded into phase-only patterns using an iterative phase retrieval algorithm with a series of random function orders in fractional Fourier transform. The results illustrate that when the extracted phase-only patterns are compressed, optical double-grayscale-image correlation can be effectively conducted without the visualization of input information at each hierarchical level in 3D space. The proposed method provides a novel strategy for 3D optical security, and can effectively enhance the flexibility for the optically secured correlation in 3D space. [ABSTRACT FROM AUTHOR]

Spiral phase plate (SPP), as a kind of optical component for generating optical vortex (OV), has the ability to convert the traditional non-singular beams into OV with spiral phase distribution. However, due to the demanding of machining accuracy, the production of high quality SPPs with large topological charges (TCs) is usually complicated and expensive. An approach to generate OV with large TCs based on low-order SPPs is presented. In the proposed scheme, the addition of TCs is realized by cascading multiple SPPs, and the double-pass configuration is employed to implement doubling of TCs. Based on the combination of cascaded and double-pass configuration, an OV with TCs as high as 28 is generated, using two SPPs of TCs 6 and 8, respectively. The method of alignment and the alignment deviation is discussed. [ABSTRACT FROM AUTHOR]

When a droplet is placed on an inclined plane, it can slide down the plane by gravitational force. This phenomenon can occur in many industrial applications such as surface coating and printing, as well as in evaluating the characteristics of a surface. The slippery droplet can be analyzed from the balance between the gravitational force and the sum of the capillary and resistance forces. Researchers have suggested various equations of force balance with several hypotheses. To increase the reliability of the force balance correlation, it is important to obtain an accurate inside velocity profile and the three-dimensional (3D) shape of a droplet. In this paper, an analysis system of the slippery droplet was developed which includes optical correction based on a ray tracing method for velocity field measurement and an ellipse fitting method for droplet shape reconstruction. These correction methods were verified by a numerical simulation and applied to a slippery droplet on an inclined plate coated with Poly methyl methacrylate (PMMA). The wall shear force calculated from the velocity field and that calculated from the force balance were in good agreement. [ABSTRACT FROM AUTHOR]

Featured Application: Structural health monitoring. 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. [ABSTRACT FROM AUTHOR]

Purpose: Noninvasive cerebral optical spectrometry is a promising candidate technology for the objective assessment physiological changes during pain perception. This study's primary objective was to test if there was a significant correlation between the changes in physiological parameters as measured by a cerebral optical spectrometry-based algorithm (real-time objective pain assessment [ROPA]) and subjective pain ratings obtained from volunteers and laboring women. Secondary aims were performance assessment using linear regression and receiver operating curve (ROC) analysis.Patients and methods: Prospective cohort study performed in Human Pain Laboratory and Labor and Delivery Unit. After institutional review board approval, we evaluated ROPA in volunteers undergoing the cold pressor test and in laboring women before and after epidural or combined spinal epidural placement. Linear regression was performed to measure correlations. ROCs and corresponding areas under the ROCs (AUC), as well as Youden's indices, as a measure of diagnostic effectiveness, were calculated.Results: Correlations between numeric rating scale or visual analog scale and ROPA were significant for both volunteers and laboring women. AUCs for both volunteers and laboring women with numeric rating scale and visual analog scale subjective pain ratings as ground truth revealed at least good (AUC: 70%–79%) to excellent (AUC >90%) distinction between clinically meaningful pain severity differentiations (no/mild–moderate–severe).Conclusion: Cerebral Optical Spectrometry-based ROPA significantly correlated with subjectively reported pain in volunteers and laboring women, and could be a useful monitor for clinical circumstances where direct assessment is not available, or to complement patient-reported pain scores. [ABSTRACT FROM AUTHOR]

Featured Application: Structural health monitoring. Correlation-domain analysis has enabled distributed measurements of Brillouin gain spectra along optical fibers with high spatial resolution, up to millimeter-scale. The method relies on the joint modulation of counter-propagating Brillouin pump and signal waves so that their complex envelopes are correlated in select positions only. Brillouin optical correlation-domain analysis was first proposed nearly 20 years ago based on frequency modulation of the two waves. This paper reviews two more recent variants of the concept. In the first, the Brillouin pump and signal waves are co-modulated by high-rate binary phase sequences. The scheme eliminates restricting trade-offs between the spatial resolution and the range of unambiguous measurements, and may also suppress noise due to residual Brillouin interactions outside the correlation peak. Sensor setups based on phase coding addressed 440,000 high-resolution points and showed potential for reaching over 2 million such points. The second approach relies on the amplified spontaneous emission of optical amplifiers, rather than the modulation of an optical carrier, as the source of Brillouin pump and signal waves. Noise-based correlation-domain analysis reaches sub-millimeter spatial resolution. The application of both techniques to tapered micro-fibers and planar waveguides is addressed as well. [ABSTRACT FROM AUTHOR]

We show a method of intensity correlation imaging of targets illuminated by a sunlight-like source both theoretically and experimentally. With a Faraday anomalous dispersion optical filter (FADOF), we have modulated the coherence time of a thermal source up to 0.167 ns. And we carried out measurements of temporal and spatial correlations, respectively, with an intensity interferometer setup. By skillfully using the even Fourier fitting on the very sparse sampling data, the images of targets are successfully reconstructed from the low signal-noise-ratio(SNR) interference pattern by applying an iterative phase retrieval algorithm. The resulting imaging quality is as well as the one obtained by the theoretical fitting. The realization of such a case will bring this technique closer to geostationary satellite imaging illuminated by sunlight. [ABSTRACT FROM AUTHOR]

The present study investigated differences in the pickup of information about the size and location of an obstacle in the path of locomotion. The main hypothesis was that information about obstacle location is most useful when it is sampled at a specific time during the approach phase, whereas information about obstacle size can be sampled at any point during the last few steps. Subjects approached and stepped over obstacles in a virtual environment viewed through a head-mounted display. In Experiment 1, a horizontal line on the ground indicating obstacle location was visible throughout the trial while information about obstacle height and depth was available only while the subject was passing through a viewing window located at one of four locations along the subject’s path. Subjects exhibited more cautious behavior when the obstacle did not become visible until they were within one step length, but walking behavior was at most weakly affected in the other viewing window conditions. In Experiment 2, the horizontal line indicating obstacle location was removed, such that no information about the obstacle (size or location) was available outside of the viewing window. Subjects adopted a more cautious strategy compared to Experiment 1 and differences between the viewing window conditions and the full vision control condition were observed across several measures. The differences in walking behavior and performance across the two experiments support the hypothesis that walkers have greater flexibility in when they can sample information about obstacle size compared to location. Such flexibility may impact gaze and locomotor control strategies, especially in more complex environments with multiple objects and obstacles. [ABSTRACT FROM AUTHOR]

Abstract: Ghost imaging uses optical correlations to enable an alternative and intriguing image acquisition technique: even though information from either one of the detectors used for the acquisition does not yield an image, an image can be obtained by harnessing the optical correlations. This Review describes a variety of both quantum and classical ghost imaging techniques, and seeks to point out where these techniques may have practical applications. [ABSTRACT FROM AUTHOR]

Optical correlation has a rich history in image recognition applications from a database. In practice, it is simple to implement optically using two lenses or numerically using two Fourier transforms. Even if correlation is a reliable method for image recognition, it may jeopardize decision making according to the location, height, and shape of the correlation peak within the correlation plane. Additionally, correlation is very sensitive to image rotation and scale. To overcome these issues, in this study, we propose a method of nonparametric modelling of the correlation plane. Our method is based on a kernel estimation of the regression function used to classify the individual images in the correlation plane. The basic idea is to improve the decision by taking into consideration the energy shape and distribution in the correlation plane. The method relies on the calculation of the Hausdorff distance between the target correlation plane (of the image to recognize) and the correlation planes obtained from the database (the correlation planes computed from the database images). Our method is tested for a face recognition application using the Pointing Head Pose Image Database (PHPID) database. Overall, the results demonstrate good performances of this method compared to competitive methods in terms of good detection and very low false alarm rates.

To enable high-speed distributed strain and temperature measurements, we have recently developed a new configuration of Brillouin optical correlation-domain reflectometry (BOCDR), called slope-assisted (SA-) BOCDR, which exploits the slope power of the Brillouin gain spectrum. Although its fundamental operations have been already clarified, a detailed study on the measurement sensitivity has not been performed yet. Here, we investigate the influences of the incident power and the spatial resolution on the measurement sensitivity of SA-BOCDR. The sensitivity is found to be improved with increasing incident power and/or lowering spatial resolution, which is verified through distributed temperature measurements. [ABSTRACT FROM AUTHOR]

Based on the extended Huygens–Fresnel integral and the theory of coherence of light field, we have investigated the correlated imaging by using the transverse normalized second-order intensity fluctuation correlation function with partially coherent light radiation. The imaging for a reflected object with relative long distance is determined by the feature of speckle-to-speckle correlation. By using the correlation function, we study the effects of imaging distance, the sizes of object lens and reference lens, the source’s transverse coherent width and its transverse size on the quality of correlated imaging. Numerical results show that the parameters of imaging system and the properties of partially coherent light source have significant influences on the imaging resolution and visibility. For an object lens with large enough diameter, the resolution is determined by the transverse coherent width of light source. On the contrary, it depends on the aperture of object lens. The magnification of the system depends only on the propagation distance. This speckle-to-speckle correlated imaging with unbalanced arms have potential applications in remote sensing due to its unique features. [ABSTRACT FROM PUBLISHER]

This paper presents an information authentication scheme using sparse representation of double random phase encoding in fractional Fourier transform domain. Different from traditional cryptographic applications, only sparse version of the ciphertext is available at the receiver end. The decrypted image is unrecognizable and of no meaningful information of the plaintext, which can enhance the resistance against various attacks. The decrypted image can be authenticated using nonlinear optical correlation approach. Numerical simulations have been carried out, and the results prove the effectiveness and noise resistance of the proposed scheme. [ABSTRACT FROM AUTHOR]

We propose a novel optical asymmetric cryptosystem combining the photon counting imaging with phase-truncated Fresnel transform, which can be used for complete information retrieval and authentication verification. The proposed combination overcomes the weakness of photon counting-based double random phase-encoding scheme. For retrieval of original image for authentication, the reverse process of phase truncation approach is followed and a nonlinear correlation filter is used. The complete information retrieval and authentication verification are possible provided sufficient number of photons is available. To check the robustness of the proposed scheme, attack analysis has been carried out. The simulation results are presented to demonstrate the proposed idea. [ABSTRACT FROM AUTHOR]

Impact traces on a composite pressure vessel were detected by measuring residual strain in aluminum (Al)-coating optical fiber for the first time. The residual strain was obtained by a Brillouin optical correlation domain analysis (BOCDA) sensor system, where a continuous optical signal was simultaneously phase-modulated to choose the sensing position, and single-side-band modulated to find the Brillouin frequency. This sensor system successfully measured the Brillouin frequency, which can be converted to the strain, along a 500 m long optical fiber, with distance resolution of less than 1.5 cm. The cantilever beam test using a bonded optical fiber presented the strain conversion coefficient, which was determined by the comparison between the measured Brillouin frequency and the strain of an electric strain gauge. Al-coating optical fiber was attached around the surface of a composite pressure vessel, and consecutive impacts at six separate positions were applied using hemisphere and wedge impactors with energies of 10, 20, and 40 J. The measured Brillouin frequencies were the unchanged intrinsic frequency along the whole fiber length, except for the six peak positions, which exactly coincided with the impact positions. The fine measurement at these peak positions showed the frequency peaks to be composed of two split peaks, which were compared with photographs taken while the impacted surfaces were deformed. This confirmed that a dent temporarily formed at an impact position caused the optical fiber to bend twice, and the strain remained at two adjacent positions. Hydraulic pressure test of the composite pressure vessel after the impacts showed that this measurement system could detect small impact traces that do not cause critical structural degradation, as well as large impact damages. [ABSTRACT FROM AUTHOR]

Iris segmentation using active contours approaches is receiving increasing attention. In this paper, a self-ruling active contour approach based on the optical correlation algorithm is proposed. The novelty of this research effort is to apply the Optical Correlation based Active Contours (OCAC) on iris segmentation and tracking and highlight the advantages of its small computation time and better accuracy performance. Optical correlation computed with a numerical simulation of the Vander Lugt correlator is used to detect iris and pupil areas which used as an initial contours. As a result, these initial contours assists the method to calculate terms in an energy expression. In the proposed method, several references images called filters of iris and pupil have been introduced. Images from four iris datasets as CASIA v4, WVU non-ideal, MMU2, UBIRIS v2, and a motion video were used in the experiments phase. To present an aggregate overview of the proposed method advantages, we computed several parameters as iris and pupil centers localization errors, iris and pupil rays errors, three performance metrics (as Jaccard coefficient, Dice coefficient, Hausdroff distance), average segmentation error, and average execution time. We compare these segmentation performance parameters with several leading techniques demonstrating significantly improved results with the proposed OCAC technique. [ABSTRACT FROM AUTHOR]

We present a three-step approach based on the commercial VIAPIX® module for road traffic sign recognition and identification. Firstly, detection in a scene of all objects having characteristics of traffic signs is performed. This is followed by a first-level recognition based on correlation which consists in making a comparison between each detected object with a set of reference images of a database. Finally, a second level of identification allows us to confirm or correct the previous identification. In this study, we perform a correlation-based analysis by combining and adapting the Vander Lugt correlator with the nonlinear joint transformation correlator (JTC). Of particular significance, this approach permits to make a reliable decision on road traffic sign identification. We further discuss a robust scheme allowing us to track a detected road traffic sign in a video sequence for the purpose of increasing the decision performance of our system. This approach can have broad practical applications in the maintenance and rehabilitation of transportation infrastructure, or for drive assistance. [ABSTRACT FROM AUTHOR]

In an earlier work of the author the time evolution of Morse oscillator was studied analytically and exactly at low temperatures whereupon optical correlation functions were calculated using Morse oscillator coherent states were employed. Morse oscillator propagator in the high temperature limit is derived and a closed form of its corresponding canonical partition function is obtained. Both diagonal and off-diagonal forms of Morse oscillator propagator are derived in the high temperature limit. Partition functions of diatomic molecules are calculated. [ABSTRACT FROM AUTHOR]

Brillouin optical correlation‐domain reflectometry (BOCDR) is one of the fibre‐optic distributed strain and temperature sensing systems. Conventionally, BOCDR has been implemented using three erbium‐doped fibre amplifiers (EDFAs) to enhance the signal‐to‐noise ratio (SNR) of the measurement. However, the use of multiple EDFAs has restricted the size and cost efficiency of the system. In this work, the authors show that, among the three EDFAs previously employed, the one in the Stokes path plays the most important role in enhancing the SNR. Subsequently, they implement BOCDR using only one EDFA and demonstrate distributed strain sensing. The measurement error is also investigated as a function of the output power of a light source. [ABSTRACT FROM AUTHOR]

The authors demonstrate distributed temperature sensing based on slope‐assisted Brillouin optical correlation‐domain reflectometry (BOCDR) with a long measurement range of >10 km. They find that to achieve such a long‐range measurement, a delay line in a reference path needs to be at least four times longer than the sensing fibre. In addition, they show that the use of such a long delay line induces forward‐propagating Brillouin‐scattered light in the reference path, which deteriorates the signal‐to‐noise ratio (SNR) of the system and should be suppressed. Finally, by exploiting a beyond‐nominal‐resolution effect of the slope‐assisted BOCDR, they detect a 3‐m‐long heated section in a 13‐km‐long silica fibre in a distributed manner; the reason for its low SNR is also discussed. [ABSTRACT FROM AUTHOR]

Slope instabilities are one of the most important geo-hazards in terms of socio-economic costs. The island of La Réunion (Indian Ocean) is affected by constant slope movements and huge landslides due to a combination of rough topography, wet tropical climate and its specific geological context. We show that remote sensing techniques (Differential SAR Interferometry and correlation of optical images) provide complementary means to characterize landslides on a regional scale. The vegetation cover generally hampers the analysis of C–band interferograms. We used JERS-1 images to show that the L-band can be used to overcome the loss of coherence observed in Radarsat C-band interferograms. Image correlation was applied to optical airborne and SPOT 5 sensors images. The two techniques were applied to a landslide near the town of Hellbourg in order to assess their performance for detecting and quantifying the ground motion associated to this landslide. They allowed the mapping of the unstable areas. Ground displacement of about 0.5 m yr-1 was measured.

A scheme to correlate optical and microwave photons is proposed in a hybrid electro-optomechanical system, where mechanical resonator is coupled to both optical and microwave fields. Analytical and numerical simulation results show that the cross-correlation function between Stokes and anti-Stokes photons strongly violates the Cauchy–Schwarz inequality, which confirms the nonclassical correlation between the optical and microwave photons. It is worth noting that the nonclassical photon pairs with vast different wavelengths, which may be useful for quantum communication, are generated under the experimentally accessible weak coupling limit rather than single-photon strong coupling regime. In addition, the protocol provides a possible route to combine the respective advantages of optical photons, microwave photons, and phonons in a hybrid electro-optomechanical system. [ABSTRACT FROM AUTHOR]

This study demonstrates the monitoring of distributed strain of rail and girder of a railway bridge occurring during train passage over the bridge’s entire section on a real-time basis by applying a developed distributed optical fiber sensor based on Brillouin Optical Correlation Domain Analysis (BOCDA). The distributed optical fiber sensor system and an algorithm to control as well as to analyze Brillouin gain spectrum signals were also developed. A single-mode optical fiber was attached in the longitudinal direction on the rail and the lower flange of the girder to be used as a sensing fiber of the BOCDA system. Changes in the girder’s strain at the center point of the bridge during the passage of a commercial train were measured at 9 Hz, and the accuracy of this measurement was validated by comparing the measured data with the data from strain gauge. In addition, the distributed strain of a girder and the rail with a length of 40.26 m was measured in real time with a spatial resolution of 31.1 cm. Based on the results of the rail’s strain distribution, the study could identify the location where excessive strain occurred due to an influence of unsupported sleepers on girder of the bridge. [ABSTRACT FROM AUTHOR]

Precise extraction of road marking features is a critical task for autonomous urban driving, augmented driver assistance, and robotics technologies. In this study, we consider an autonomous system allowing us lane detection for marked urban roads and analysis of their features. The task is to relate the georeferencing of road markings from images obtained using the VIAPIX® system. Based on inverse perspective mapping and color segmentation to detect all white objects existing on this road, the present algorithm enables us to examine these images automatically and rapidly and also to get information on road marks, their surface conditions, and their georeferencing. This algorithm allows detecting all road markings and identifying some of them by making use of a phase-only correlation filter (POF). We illustrate this algorithm and its robustness by applying it to a variety of relevant scenarios. [ABSTRACT FROM AUTHOR]

This paper considers the derivation of the relations existing between the incident, reflected (refracted) wavefronts and the reflecting surface (surface of discontinuity) by making use of the most unambiguous generalized vectorial laws of reflection and refraction developed by the author in 2015. The cases of reflection of a plane wavefront by plane as well as convex reflecting surfaces have been considered along with the cases of refraction of a plane wavefront by plane as well as concave spherical surfaces of discontinuity for the derivation of the concerned relations. All the relations offered are being claimed to be novel and the relations derived in cases of reflection (refraction) of a plane wavefront by a plane reflecting surface (plane surface of discontinuity) appear to be the most simple and elegant. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the distribution of total high-order aberrations (HOAs) Z 3 ±1 , Z 4 0 , and Z 3 ±3 of anterior cornea and their correlations to astigmatism. In addition, the relationship between different axes of astigmatism and Z 3 −1 or Z 3 1 was analyzed. The HOAs in the central 6-mm zone of the cornea were measured with an iTrace wavefront analyzer in 556 cataractous eyes at the Tianjin Eye Hospital in China. Simulated keratoscope readings (Sim k ) were also measured with the analyzer. The corneal total HOAs Z 3 ±1 , Z 4 0 and Z 3 ±3 exhibited a non-normal distribution. Significant correlations were found between the topographic-simulated keratometric power (ΔSim k ) with the axis at 180° ± 5° and absolute value of Z 3 −1 ( P = 0.008), the ΔSim k with the axis at 90° ± 5° and absolute value of Z 3 1 ( P < 0.001), and the ΔSim k and total HOAs ( P < 0.001), Z 3 ±1 ( P < 0.001), and Z 3 ±3 ( P < 0.001). No significant correlation was found between ΔSim k and Z 4 0 ( P = 0.404). In conclusion, corneal astigmatism with the axis near the horizontal position was mainly associated with the value of Z 3 −1 . Corneal astigmatism with the axis near the vertical position was mainly related to the value of Z 3 1 . HOAs except Z 4 0 are correlated with astigmatism. [ABSTRACT FROM AUTHOR]