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Revisiting the generalized polar decomposition ofMueller matrices

Christian Heinrich, Jean Rehbinder, and Jihad Zallat

DOI: 10.1364/JOSAA.394099 Received 01 Apr 2020; Accepted 10 Jul 2020; Posted 10 Jul 2020  View: PDF

Abstract: Mueller polarimetry is a powerful imaging modality which has been successfully applied to various application fields. Decomposition of Mueller matrices in elementary components is classically consideredin order to unfold complex physical phenomena taking place in probed samples or scenes. In this context, the generalized polar decomposition, also known as the Lu and Chipman decomposition, is playinga prominent role. In this article, we show that the set of candidate generalized polar decompositions isricher than the set used so far. Negative-determinant Mueller matrices are naturally addressed in theproposed framework. We show that taking into account those supplementary polar decompositions addresses issues raised in the literature. Application is carried out on synthetic and on measured Muellermatrices

Optimization methods for achieving high diffractionefficiency with perfect electric conducting gratings

Rubén Aylwin, Gerardo Silva, Carlos Jerez-Hanckes, and Patrick Fay

DOI: 10.1364/JOSAA.394204 Received 31 Mar 2020; Accepted 10 Jul 2020; Posted 10 Jul 2020  View: PDF

Abstract: This work presents the implementation, numerical examples and experimental convergence study of firstand second-order optimization methods applied to onedimensional periodic gratings. Through boundary integral equations and shape derivatives, the profile of agrating is optimized such that it maximizes the diffraction efficiency for given diffraction modes for transverse electric polarization. We provide a thorough comparison of three different optimization methods: a firstorder method (gradient descent); a second-order approach based on a Newton iteration, where the usualNewton step is replaced by taking the absolute value ofthe eigenvalues given by the spectral decomposition ofthe Hessian matrix to deal with non-convexity; and theBroyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm,a quasi-Newton method. Numerical examples are provided to validate our claims. Moreover, two grating profiles are designed for high efficiency in the Littrow configuration and then compared to a high efficiency commercial grating. Conclusions and recommendations,derived from the numerical experiments, are providedas well as future research avenues.

Optical Properties of Biosynthesized Nano-scaledEu2O3 for Red Luminescence Applications

Hamza Mohamed, Khoula Hkiri, Mohammed Khenfouch, Simon Dhlamini, Mohamed Henini, and maaza malik

DOI: 10.1364/JOSAA.396244 Received 27 Apr 2020; Accepted 10 Jul 2020; Posted 10 Jul 2020  View: PDF

Abstract: This contribution reports on the optical properties of bio-synthesised Eu2O3 nanoparticles bio-engineered for the firsttime by a green and cost effective method using aqueous fruit extracts of Hyphaene thebaica as an effective chelatingand capping agent. The morphology, structural and optical properties of the samples annealed at 500o C were confirmedby using high resolution transmission electron microscope (HR-TEM), X-Ray diffraction analysis (XRD), UV-vis spectrocopyand PL spectrometer. The XRD results confirmed the characteristic body centered cubic (bcc) structure of Eu2O3nanoparticles with an average size of 20 nm. HR-TEM revealed square type morphology with an average size of ~ 6 nm.Electron Dispersion Energy dispersive X-ray Spectroscopy (EDS) spectrum confirmed the elemental single phase nature ofpure Eu2O3. Furthuremore, the FTIR spectroscopy revealed the intrinsic characteristic peaks of Eu–O bond stretchingvibrations. UV-vis reflectance proved that Eu2O3 absorbs in a wide range of the solar spectru from VUV-UV region withbandgap of 5.1 eV. The luminescence properties of such cubic were characterized by an intense red emission centered at614 nm. It was observed that the biosynthesized Eu2O3 nanoparticles exhibit an efficient red-luminescence & hence apotential material as red phosphor.

Linear Canonical Transform as a tool to analysecoherence properties of Electromagnetic beamspropagating in a Quadratic Phase System

Aravindkumar Yelashetty, NITIKA GUPTA, Devnath Dhirhe, and Unnikrishnan Gopinathan

DOI: 10.1364/JOSAA.395777 Received 21 Apr 2020; Accepted 08 Jul 2020; Posted 08 Jul 2020  View: PDF

Abstract: Linear Canonical Transformation (LCT) provides a generalised and elegant mathematical framework foranalysing the coherence properties of an Electromagnetic beam propagating in Quadratic Phase Systems(QPS). It is shown that LCT may be used to analyse the coherence properties like Generalised Stokes Parameters (GSP) and Electromagnetic Degree of Coherence (EM-DOC) of a partially coherent electromagnetic beam propagating through a QPS. We present simulation results of Gaussian Schell model beampropagating through Fourier System, Fractional Fourier system, 4-f Imaging system with aperture andBeam Relay system.

Onset times of long-lived rogue waves in anoptical waveguide array

Chad Pelwan, Alex Quandt, and Robert Warmbier

DOI: 10.1364/JOSAA.398631 Received 26 May 2020; Accepted 07 Jul 2020; Posted 08 Jul 2020  View: PDF

Abstract: We study the effects of increasing modulation instability and disorder on the onsettimes of rogue waves in waveguide arrays as described by the discrete unstable nonlinearSchrödinger equation (UNLSE). We analytically determine regions of instability, where roguewaves are likely to occur in the UNLSE and then use numerical techniques to study the timeevolution of these systems. Only for small modulation instability, the effect of the fluctuations isprominent on the onset times but otherwise we find that large modulation instability dominatesthe onset time behaviour.

State-of-the-art active optical techniques forthree-dimensional surface metrology: a review

Andres Marrugo, Feng Gao, and Song Zhang

DOI: 10.1364/JOSAA.398644 Received 27 May 2020; Accepted 07 Jul 2020; Posted 08 Jul 2020  View: PDF

Abstract: This paper reviews recent developments of non-contact 3D three-dimensional (3D) surface metrologyusing an active structured optical probe. We primarily focus on those active non-contact 3D surface measurement techniques that could be applicable to the manufacturing industry. We discuss principles ofeach technology, and its advantageous characteristics as well as limitations. Towards the end, we willdiscuss our perspectives on the current technological challenges in designing and implementing thesemethods in practical applications.

Singular Value Decomposition Approach toCoherent Averaging in Digital Holography

Samuel Park, Samuel Thurman, Ryan Lindle, Abbie Watnik, Paul Lebow, and Andrew Bratcher

DOI: 10.1364/JOSAA.392645 Received 01 Apr 2020; Accepted 07 Jul 2020; Posted 08 Jul 2020  View: PDF

Abstract: We present a new approach to coherent averaging in digital holography using singularvalue decomposition (SVD). Digital holography enables the extraction of phase informationfrom intensity measurements. For this reason, SVD can be used to statistically determine theorthogonal vectors that align the complex-valued measurements from multiple frames and groupcommon modes accounting for constant phase shift terms. The SVD approach enables theseparation of multiple signals, which can be applied to remove undesired artifacts such as scatterin retrieved images. The advantages of the SVD approach are demonstrated here in experimentsthrough fog-degraded holograms with spatially incoherent and coherent scatter.

Propagation characteristics of Gaussian-Schell model beamsthrough optical systems in Kerr media


DOI: 10.1364/JOSAA.397629 Received 13 May 2020; Accepted 03 Jul 2020; Posted 06 Jul 2020  View: PDF

Abstract: For the beam spreading case, the propagation formulae of Gaussian–Schell model (GSM) beams through general opticalsystems in Kerr media are derived, and the propagation characteristics of GSM beams through an ideal thin lens inKerr media are studied in detail. It is shown that the size and position of the beam waist can be controlled by the Kerreffect. Furthermore, the formula of focal shift of GSM beams focused by an ideal thin lens in Kerr media is also derived.It is found that in self-focusing media the focal shift decreases as the beam power or the beam coherence degreeincreases. In addition, there exists a maximum of the focal shift, and the formula of the focal shift maximum is derived.On the other hand, for the beam self-focusing case, the focusing characteristics of GSM beams focused by an ideal thinlens in Kerr media is also investigated.

Physiological wound assessment from coregisteredand segmented tissue hemoglobin maps

Edwin Robledo, Richard Schutzman, Ruogu Fang, Cristianne Fernandez, Rebecca Kwasinski, Kevin Leiva, Francisco Perez-Clavijo, and Anuradha Godavarty

DOI: 10.1364/JOSAA.394985 Received 15 Apr 2020; Accepted 02 Jul 2020; Posted 02 Jul 2020  View: PDF

Abstract: A hand-held near-infrared optical scanner (NIROS) was recently developed to map for effective changes in oxyand deoxy-hemoglobin concentration in diabetic foot ulcers (DFUs) across weeks of treatment. Herein, acoregistration and image segmentation approach was implemented to overlay hemoglobin maps onto the whitelight images of ulcers. Validation studies demonstrated over 97% accuracy in coregistration. Coregistration wasfurther applied to a healing DFU across weeks of healing. The potential to predict changes in wound healing wasobserved when comparing the coregistered and segmented hemoglobin concentration area maps to the visualarea of the wound.

Development of Ultra Stable Fibre Optic Timeand Frequency Reference Networks in Africa

Shukree Wassin, Kagiso Leburu, George Isoe, and Tim Gibbon

DOI: 10.1364/JOSAA.396201 Received 27 Apr 2020; Accepted 02 Jul 2020; Posted 06 Jul 2020  View: PDF

Abstract: The unparalleled accuracy of modern-day atomic clocks has stimulated thedevelopment of time and frequency comparison techniques, with optical frequency transferover fibre networks emerging as the preferred method. It has been demonstrated thatfrequency transfer over optical fibres has an order-of-magnitude better stability and accuracythan traditional satellite-based techniques. Precise time has become an essential service formost critical infrastructure and applications. New progress in LTE and 5G will demand moreaccess to precise time with accuracies of under 10 nanoseconds. Although this technologyexists in Africa, continuous improvements are required. With the arrival of the SquareKilometer Array (SKA) in Africa, the National Metrology Institute of South Africa (NMISA)upgraded its time and frequency infrastructure in order to support the stringent time accuracyrequirements of MeerKAT and SKA telescope. Over the past five years, the Centre forBroadband Communication at the Nelson Mandela University has been conducting excitingand cutting-edge research looking at new and innovative ways for coherently disseminatinghigh-speed data and clock over optical fibre networks. This paper reports on recent researchprogress made in developing synchronous optical networks in South Africa and across theAfrican continent. This paper begins by presenting a pioneering all-optical approach formeasuring the round-trip latency time along a spooled G. 652 single mode fibre. This hasbeen realized by optically injecting a pulse-per-second (PPS) signal from a distributedfeedback (DFB) laser into the slave mode of a 1550 nm vertical cavity surface emitting laser(VCSEL) located at the receiver end. A round-trip fibre time delay of 113.2 μs wasexperimentally measured over a 22 km. Furthermore, the jitter instability of an opticallymodulated PPS was measured as a function of temperature. A jitter of 434.82 ps wasmeasured during the night-to-day temperature cycle (5 °C - 25 °C). The impact ofpolarization fluctuations on jitter stability is presented. A maximum jitter of 417.88 ps wasmeasured for the transmitted PPS along the aerial fibre. Lastly, a novel technique fordistributing a stable microwave reference frequency, using an intensity modulated VCSEL ispresented. The novel frequency dissemination and synchronisation system proposes the use ofa VCSEL based phase correction actuator together with the inherent chromatic dispersionproperties of the fibre. Frequency instabilities of 4.18939 × 10−12 at 104 s without active noisecancellation and 4.86 × 10−14 at 104 s with active noise cancellation was successfullymeasured across the 26 km G.655 fibre link.

Numerical model of Er3+/Yb3+ co-doped sevencore fiber amplifier for space divisionmultiplexing system

Ali Nassiri, abdelkader boulezhar, and Hafida Idrissi Azami

DOI: 10.1364/JOSAA.396488 Received 28 Apr 2020; Accepted 02 Jul 2020; Posted 06 Jul 2020  View: PDF

Abstract: Space Division Multiplexing (SDM) erbium doped seven-core fiber amplifier(EDFA) is increasingly attracting interest due to their performances to improve the capacitytransmission systems. To increase the gain and improve the characteristics of SDM sevencore fiber amplifier, this paper proposes the use of the Erbium/Ytterbium (Er3+/Yb3+) codoped seven-core fiber amplifier. A theoretical model of SDM co-doped seven-core fiberamplifier is developed. The presented results show that the proposed model allows to obtain apeak gain over 60 dB at a wavelength of 1543 nm, a large bandwidth of 64 nm with a gaingreater than 20 dB and with a minimum noise which is lower than 6 dB.

Colour difference evaluation for wide colourgamut displays

Baiyue Zhao, Qiang Xu, and Ming Luo

DOI: 10.1364/JOSAA.394132 Received 31 Mar 2020; Accepted 01 Jul 2020; Posted 02 Jul 2020  View: PDF

Abstract: With the emerging demand for wide colour gamut displays, an issue has beenraised that the commonly used colour difference formulae or uniform colour spaces whichwere derived based on the data produced in the relatively smaller colour gamut could beunreliable for predicting colour differences in the highly saturated colour regions. Apsychophysical experiment was carried out for evaluating colour difference at a luminancelevel of 310 cd/m2 on a wide colour gamut (WCG) display with approximate DCI-P3 colourgamut. Twelve colour centres were selected to cover the entire gamut boundary. There were192 pairs of samples over 12 colour centres judged by 18 observers using grey-scalepsychophysical method. The data set was used to test the performance of six uniform colourspaces and colour difference equations, CIELAB, CIEDE2000, CAM02-UCS, Jzazbz, ICTCP,nICTCP, a newly revised ICTCP formula. The colour discrimination ellipses were used to testlocal and global uniformity of colour spaces and compared with previous studies. The resultsrevealed that all formulae improved their performance to have a lightness parametric factorabout 0.5. CAM02-UCS significantly outperformed the others in overall, and local and globaluniformity. The high-quality visual data set is recommended to evaluate or to derive colourdifference formulae for wide colour gamut applications in the future.

Approaching Quantum-Limited ImagingResolution without Prior Knowledge of theObject Location

Michael Grace, Zachary Dutton, Amit Ashok, and Saikat Guha

DOI: 10.1364/JOSAA.392116 Received 06 Mar 2020; Accepted 30 Jun 2020; Posted 30 Jun 2020  View: PDF

Abstract: Passive imaging receivers that demultiplex an incoherent optical field into a set oforthogonal spatial modes prior to detection can surpass canonical diffraction limits on spatialresolution. However, these mode-sorting receivers exhibit sensitivity to contextual nuisanceparameters (e.g., the centroid of a clustered or extended object), raising questions on theirviability in realistic scenarios where prior information about the scene is limited. We propose amulti-stage detection strategy that segments the total recording time between different physicalmeasurements to build up the required prior information for near quantum-optimal imagingperformance at sub-Rayleigh length scales. We show via Monte Carlo simulations that anadaptive two-stage scheme that dynamically allocates recording time between a conventionaldirect detection measurement and a binary mode sorter outperforms idealized direct detectionalone when no prior knowledge of the object centroid is available, achieving one to two ordersof magnitude improvement in mean squared error for simple estimation tasks. Our scheme canbe generalized for more sophisticated tasks involving multiple parameters and/or minimal priorinformation.

Multi-view fringe projection system for surface topography measurement during metal powder bed fusion

Andrew Dickins, Taufiq Widjanarko, Danny Sims-Waterhouse, Adam Thompson, Simon Lawes, and Richard Leach

DOI: 10.1364/JOSAA.396186 Received 29 Apr 2020; Accepted 29 Jun 2020; Posted 30 Jun 2020  View: PDF

Abstract: Metal powder bed fusion (PBF) methods need in-process measurement methods to increase user confidence and encourage further adoption in high-value manufacturing sectors. In this paper, a novel measurement method for PBF systems is proposed that uses multi-view fringe projection to acquire high-resolution surface topography information of the powder bed. Measurements were made using a mock-up of a commercial PBF system to assess the system’s accuracy and precision in comparison to conventional single-view fringe projection techniques for the same application. Results show that the multi-view system is more accurate, but less precise, than single view fringe projection on a point-by-point basis. The multi-view system also achieves a high degree of surface coverage by using alternate views to access areas not measured by a single camera.

Introduction to electromagnetic scattering, partII: tutorial

Fabrizio Frezza, fabio mangini, and Nicola Tedeschi

DOI: 10.1364/JOSAA.381104 Received 23 Oct 2019; Accepted 28 Jun 2020; Posted 29 Jun 2020  View: PDF

Abstract: In this paper, some generalizations of electromagnetic scattering problems byelementary shapes are presented. In particular, the aim of the paper is to provide solutions for thescattering problem by multiple objects with simple shapes, either in concentric configurationor arbitrarily distributed in the space. The vector harmonics, representing the fields, and theirproperties are applied in order to solve five different problems: the electromagnetic scattering byan infinitely long circular stratified cylinder, by a multilayered sphere, by an ensemble of parallelcylinders, by an ensemble of multi-spheres, and ultimately by a sphere embedded in a circularcylinder. Numerical results in particularly important configurations are shown.

Laser – induced autofluorescence assisted bymultivariate techniques discriminates cataractouslens from healthy lens tissues of Sprague – Dawleyrats

Peter Adueming, Eghan Moses, Benjamin Anderson, Samuel Kyei, Jerry Opoku-Ansah, Charles Amuah, Charles Takyi, and Paul Buah-Bassuah

DOI: 10.1364/JOSAA.394555 Received 08 Apr 2020; Accepted 24 Jun 2020; Posted 26 Jun 2020  View: PDF

Abstract: Laser-induced autofluorescence (LIAF) combined with multivariate techniques, has been used to discriminatecataractous lens from healthy lens tissues. In this study, 405 nm and 445 nm were used as excitation sources to inducethe autofluorescence. Results show high autofluorescence intensity in cataractous lens tissues than in healthy ones.Cataractous lens tissues show a red shift of 0.9 nm and 1.2 nm at 405 nm and 445 nm excitations, respectively. Usingprincipal component analysis (PCA), 3 principal components (PCs) gave more than 99 % variability for both 405 nmand 445 nm excitation sources. Based on the 3 PCs, Fisher’s linear discriminant model was developed. An accuracy of100 % was obtained in classifying the lens tissues using Fisher’s linear discriminant analysis (FLDA). The LIAFtechnique assisted by PCA and FLDA may be used for objective discrimination of cataractous lens from healthy lenstissues of Sprague-Dawley rats.

Far-field modeling of obstructed Laguerre-Gaussbeams

Bencheikh Abdelhalim, saoussen chabou, and Ouis BOUMEDDINE

DOI: 10.1364/JOSAA.398617 Received 01 Jun 2020; Accepted 24 Jun 2020; Posted 26 Jun 2020  View: PDF

Abstract: It was shown in the paper "Opt lett, V.40 ,N.16, 2015 " that Laguerre-Gauss beams (LGBn) of order n andBessel beams (BB) are asymptotically equivalent for n 1. Here, we demonstrate that an LGBn and a BBare equivalent just in the inner multi-ring parts of the two beams. However, the outer multi-ring parts arecompletely different, this leads us to apply a truncation on the two beams to make them indistinguishable.Since the LGBn could be approximated by a BB just in the inner multi-ring part, we suggest another beamthat could replace its outer multi-ring part. By considering the LGBn as a sum of n rings having differentradii and widths, we model the LGBn outer multi-ring part, by a sum of what we call in this paper "ringshifted-Gaussian beams". The peer-to-peer comparison of the LGBn with the two cited beams, allowed usto provide a new analytical description of the obstructed LGBn far-field. These results will be very usefulto study many aspects related to the LGBn diffraction by apertures and stops. As an example, we show atthe end of this paper, how the self-healing ability of an obstructed LGBn could be studied analytically.

Goniochromatic assessment of gray scalesfor color change

Alejandro Ferrero, Berta Bernad, Joaquin Campos-Acosta, Noël RICHARD, Christine Fernandez-Maloigne, and Manuel Melgosa

DOI: 10.1364/JOSAA.394170 Received 24 Apr 2020; Accepted 23 Jun 2020; Posted 26 Jun 2020  View: PDF

Abstract: The dependence of color differences on the illumination and viewing directions fortwo widely-used gray scales for color change (SDCE and AATCC) was evaluated throughmeasuring the spectral bidirectional reflectance distribution function (BRDF) by a goniospectrophotometer of metrological quality. Large incidence and viewing angles must bespecially avoided using these gray scales because in these conditions color differences varyconsiderably from those established in ISO 105-A02 and ASTM D2616-12. While the visualappearance of the SDCE and AATCC gray scales for color change is similar, our resultsindicate that their goniochromatic properties are different. Finally, some recommendationsregarding observation distance and illumination angle to correctly use these gray scales forvisual experiments are given.

Digital Stokes polarimetry and its application tostructured light: tutorial

Keshaan Singh, Najmeh TabeBordbar, Andrew Forbes, and Angela Dudley

DOI: 10.1364/JOSAA.397912 Received 18 May 2020; Accepted 22 Jun 2020; Posted 29 Jun 2020  View: PDF

Abstract: Stokes polarimetry is a mature topic in optics, most commonly performed to extract the polarisation structure of optical fields for a range of diverse applications. For historical reasons, most Stokes polarimetryapproaches are based on static optical polarisation components that must be manually adjusted, prohibiting automated, real-time analysis of fast changing fields. Here we provide a tutorial on performing Stokespolarimetry in an all-digital approach, exploiting a modern optical toolkit based on liquid crystal on silicon spatial light modulators and digital micromirror devices. We explain in a tutorial fashion how toimplement two digital approaches, based on these two devices, for extracting Stokes parameters in a fast,cheap and dynamic manner. After outlining the core concepts, we demonstrate their applicability to themodern topic of structured light, and highlight some common experimental issues. In particular, we illustrate how digital Stokes polarimetry can be used to measure key optical parameters such as the stateof polarisation, degree of vectorness and intra-modal phase of complex light fields.

Comparison of Sensitivity to Beam Collimation of Holographic Shearing Interferometer with Wedge Plate Shearing Interferometer and Talbot Shearing Interferometer

Rajiv Dubey and Raj Kumar

DOI: 10.1364/JOSAA.393901 Received 31 Mar 2020; Accepted 21 Jun 2020; Posted 22 Jun 2020  View: PDF

Abstract: High sensitivity of collimation testing equipments is desirable where collimated beams are used for precision and accurate measurements. Precision in setting of collimation depends on the sensitivity of the testing equipment. In present work, sensitivity to beam collimation of recently reported holographic shearing interferometer (HSI) [J. Opt. 20 (2018) 055603] is measured and compared with sensitivities of other collimation testing techniques based on wedge plate shearing interferometer and Talbot shearing interferometer. For a test beam of diameter 25 mm from a He-Ne laser and displacement of collimating lens by 1 mm from collimation position, Talbot shearing interferometer shows rotation of interference fringes from the horizontal direction by 2˚, wedge plate shearing interferometer shows 20˚, and HSI shows 25˚. Sensitivity is also presented in terms of measured slopes of phase maps of the recorded interferograms for 1 mm displacement of collimating lens and is obtained as 0.98 mili-radian, 15 mili-radian and 19 mili-radian corresponding to Talbot shearing interferometer, wedge plate shearing interferometer and holographic shearing interferometer respectively. The effect of de-collimation of laser beam on the interference fringes of diffraction Lloyd mirror interferometer is also demonstrated. Theoretical concepts and experimental results are presented and discussed for the above mentioned beam collimation testing techniques.

Confocal chromatic sensor with actively tilted lens for 3D measurement

Martin Fuerst, Ernst Csencsics, Christian Haider, and Georg Schitter

DOI: 10.1364/JOSAA.394212 Received 01 Apr 2020; Accepted 21 Jun 2020; Posted 23 Jun 2020  View: PDF

Abstract: Confocal chromatic displacement sensors are versatile and precise sensors formeasuring the distance to a single point. In order to obtain a 3D measurement device, thispaper presents an integrated scanning sensor design, which employs a tilting lens mechanism formanipulating the light path of the sensor. The optical implications of the design are analyticallymodeled and simulated. An experimental setup is constructed to evaluate the system design andto test its performance on a variety of samples. Results show good agreement with the simulationsand modeling, with maximal tip/tilt angles of ±2.5◦, the setup is capable of measuring a volumeof 1.7 × 1.7 × 1 mm3 with a lateral resolution of 24.8 µm and an axial resolution of 3 µm.

On-machine surface defect detection usinglight scattering and deep learning

Mingyu Liu, Benny Cheung, Nicola Senin, Shixiang Wang, Rong Su, and Richard Leach

DOI: 10.1364/JOSAA.394102 Received 01 Apr 2020; Accepted 16 Jun 2020; Posted 16 Jun 2020  View: PDF

Abstract: This paper presents an on-machine surface defect detection system using lightscattering and deep learning. A supervised deep learning model is used to mine theinformation related to defects from light scattering patterns. A convolutional neural networkis trained on a large dataset of scattering patterns that are predicted by a rigorous forwardscattering model. The model is valid for any surface topography with homogeneous materialsand has been verified by comparing with experimental data. Once the neural network istrained, it allows for fast, accurate and robust defect detection. The system capability isvalidated on micro-structured surfaces produced by ultra-precision diamond machining.

VO2 based active tunable emittance thermochromicflexible coatings

Nagla Numan, Boitumelo Mabakachaba, aline simo, Zebib Nuru, and maaza malik

DOI: 10.1364/JOSAA.395647 Received 22 Apr 2020; Accepted 09 Jun 2020; Posted 10 Jun 2020  View: PDF

Abstract: This contribution reports, for the first time, on the VO2 based thin film coatings onto flexible Al substratesexhibiting a tunable positive emittance-switching Δε=(εH- εL)>0. More precisely, the layered stack of a- Si:H/SiO2/VO2 onto flexible Al sheets presents a minimum and maximum values of emissivity of about 0.18 and 0.57 at40 ºC and 83 ºC respectively and hence allows an emittance-switching Δε of 0.39 and a relative variation Δε/εΛ of~217%. Such variations fit with the potential applications of such coatings as Smart Radiation Devices (SRD) insmall satellites and spacecraft.

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