• warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.
  • warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone. in /home/opticist/public_html/modules/aggregator/aggregator.pages.inc on line 259.

Feed aggregator

Polarization-insensitive, ultra-broadband, and compact metamaterial-inspired optical absorber via wide-angle and highly efficient performances

Applied Optics - Thu, 05/03/2018 - 01:00
Mohammad Mehrabi, Hamid Rajabalipanah, Ali Abdolali, Majid Tayarani
Because of exhibiting extraordinary features, metamaterial absorbers have captured considerable attention in recent years, especially at visible frequencies. In this paper, a new design of a metamaterial-inspired perfect visible absorber (MIPVA) is investigated, which exhibits ultra-broadband, ... [Appl. Opt. 57, 3693-3703 (2018)]
Categories: Optics news

IGA-rule 17 for performance estimation of wavelength-extended InGaAs photodetectors: validity and limitations

Applied Optics - Wed, 05/02/2018 - 01:00
Yong-Gang Zhang, Yi Gu, Xing-You Chen, Ying-Jie Ma, Xue Li, Xiu-Mei Shao, Hai-Mei Gong, Jia-Xiong Fang
A rule of thumb, denoted as IGA-rule 17, has been developed to describe the temperature and cutoff wavelength-dependent dark currents of wavelength-extended InGaAs photodetectors in a 2–3 μm band. The validity and limitations of the rule are discussed. This rule is intended as ... [Appl. Opt. 57, D141-D144 (2018)]
Categories: Optics news

Signature of phase singularities in diffusive regimes in disordered waveguide lattices: interplay and qualitative analysis

Applied Optics - Wed, 05/02/2018 - 01:00
Somnath Ghosh
Coexistence and interplay between mesoscopic light dynamics with singular optics in spatially disordered waveguide lattices are reported. Two CW light beams of a 1.55 μm operating wavelength are launched as inputs to 1D waveguide lattices with controllable weak disorder in a complex ... [Appl. Opt. 57, 3669-3673 (2018)]
Categories: Optics news

Silicon microsphere whispering gallery modes excited by femtosecond-laser-inscribed glass waveguides

Applied Optics - Wed, 05/02/2018 - 01:00
Hüseyin Ozan Çirkinoğlu, Mustafa Mert Bayer, Ulaş Sabahattin Gökay, Ali Serpengüzel, Belén Sotillo, Vibhav Bharadwaj, Roberta Ramponi, Shane Michael Eaton
We report on the coupling of whispering gallery modes in a 500-μm-radius silicon microsphere to a femtosecond-laser-inscribed glass optical waveguide. The shallow glass waveguide with a large mode field diameter in the near-infrared is written at a depth of 25 μm below the ... [Appl. Opt. 57, 3687-3692 (2018)]
Categories: Optics news

Unimorph mirror for adaptive optics in space telescopes

Applied Optics - Wed, 05/02/2018 - 01:00
David Alaluf, Renaud Bastaits, Kainan Wang, Mihaita Horodinca, Grégory Martic, Bilal Mokrani, André Preumont
This paper presents a unimorph deformable mirror intended to be used as secondary corrector in space telescopes. The deformable mirror consists of a single-crystal silicon wafer (76.2 mm diameter, 500 μm thickness) covered with an optical coating on the front side and an array ... [Appl. Opt. 57, 3629-3638 (2018)]
Categories: Optics news

Design of an ultrasensitive SPR biosensor based on a graphene-MoS_2 hybrid structure with a MgF_2 prism

Applied Optics - Wed, 05/02/2018 - 01:00
Yuncai Feng, Youwen Liu, Jinghua Teng
We propose, to the best of our knowledge, a new configuration of a biosensor based on the graphene-MoS_2 hybrid structure by adopting the lower refractive index MgF_2 prism in order to improve the sensitivity and the figure of merit (FOM). We can obtain an ultrasensitive sensor with values of ... [Appl. Opt. 57, 3639-3644 (2018)]
Categories: Optics news

Gamma and gamma-coupled beams

Applied Optics - Wed, 05/02/2018 - 01:00
Andrey G. Sedukhin
A new class of scalar, rotationally symmetric Gaussian-like beams is introduced. The slowly varying amplitudes of such beams are represented as analytical solutions to the paraxial wave equation, described in terms of the incomplete gamma functions and their products with quadratic exponential and ... [Appl. Opt. 57, 3653-3660 (2018)]
Categories: Optics news

Attojoule-efficient graphene optical modulators

Applied Optics - Mon, 04/23/2018 - 01:00
Rubab Amin, Zhizhen Ma, Rishi Maiti, Sikandar Khan, Jacob B. Khurgin, Hamed Dalir, Volker J. Sorger
Electro-optic modulation is a technology-relevant function for signal keying, beam steering, or neuromorphic computing through providing the nonlinear activation function of a perceptron. With silicon-based modulators being bulky and inefficient, here we discuss graphene-based devices ... [Appl. Opt. 57, D130-D140 (2018)]
Categories: Optics news

Optimized robotic setup for automated active thermography using advanced path planning and visibility study

Applied Optics - Fri, 04/20/2018 - 01:00
J. Peeters, B. Bogaerts, S. Sels, B. Ribbens, J. J. J. Dirckx, G. Steenackers
In-line inspection of advanced components remains a challenging task in industry. The authors will describe an automated methodology that uses numerical simulations to automatically determine the best set of experimental parameters to inspect the structure on defects using active thermography. The ... [Appl. Opt. 57, D123-D129 (2018)]
Categories: Optics news

Noninvasive assessment of skin structure by combined photothermal radiometry and optical spectroscopy: coregistration with multiphoton microscopy

Applied Optics - Thu, 04/19/2018 - 01:00
Nina Verdel, Griffin Lentsch, Mihaela Balu, Bruce J. Tromberg, Boris Majaron
We are combining two optical techniques, pulsed photothermal radiometry (PPTR) and diffuse reflectance spectroscopy (DRS), for noninvasive assessment of the structure and composition of human skin in vivo. The analysis involves simultaneous multidimensional fitting of the measured PPTR signals and ... [Appl. Opt. 57, D117-D122 (2018)]
Categories: Optics news

Exploiting fusion architectures for multispectral pedestrian detection and segmentation

Applied Optics - Wed, 04/18/2018 - 01:00
Dayan Guan, Yanpeng Cao, Jiangxin Yang, Yanlong Cao, Christel-Loic Tisse
Recent research has demonstrated that the fusion of complementary information captured by multi-modal sensors (visible and infrared cameras) enables robust pedestrian detection under various surveillance situations (e.g., daytime and nighttime). In this paper, we investigate a number of ... [Appl. Opt. 57, D108-D116 (2018)]
Categories: Optics news

Deep learning enhancement of infrared face images using generative adversarial networks

Applied Optics - Mon, 04/16/2018 - 01:00
Axel-Christian Guei, Moulay Akhloufi
This work presents a deep learning framework based on the use of deep convolutional generative adversarial networks (DCGAN) for infrared face image super-resolution. We use DCGAN for upscaling the images by a factor of 4×4, starting at a size of 16×16 and obtaining a 64×64 face ... [Appl. Opt. 57, D98-D107 (2018)]
Categories: Optics news

Structured light stereo catadioptric scanner based on a spherical mirror

Optics and Lasers in Engineering - Sun, 04/15/2018 - 06:03
Publication date: August 2018
Source:Optics and Lasers in Engineering, Volume 107

Author(s): S. Barone, P. Neri, A. Paoli, A.V. Razionale

The present paper describes the development and characterization of a structured light stereo catadioptric scanner for the omnidirectional reconstruction of internal surfaces. The proposed approach integrates two digital cameras, a multimedia projector and a spherical mirror, which is used to project the structured light patterns generated by the light emitter and, at the same time, to reflect into the cameras the modulated fringe patterns diffused from the target surface. The adopted optical setup defines a non-central catadioptric system, thus relaxing any geometrical constraint in the relative placement between optical devices. An analytical solution for the reflection on a spherical surface is proposed with the aim at modelling forward and backward projection tasks for a non-central catadioptric setup. The feasibility of the proposed active catadioptric scanner has been verified by reconstructing various target surfaces. Results demonstrated a great influence of the target surface distance from the mirror's centre on the measurement accuracy. The adopted optical configuration allows the definition of a metrological 3D scanner for surfaces disposed within 120 mm from the mirror centre.





Categories: Optics news

Low-speed-camera-array-based high-speed three-dimensional deformation measurement method: Principle, validation, and application

Optics and Lasers in Engineering - Sun, 04/15/2018 - 06:03
Publication date: August 2018
Source:Optics and Lasers in Engineering, Volume 107

Author(s): Ran Chen, Zhongwei Li, Kai Zhong, Xingjian Liu, Yuh Jin Chao, Yusheng Shi

High-resolution imaging devices are of interest in the development of accurate 3D vision systems. However, it is challenging to achieve a balance between the image capturing speed and resolution. The image capturing speed is relatively low for high-resolution imaging devices, which restricts their applications in high-speed 3D measurements. Therefore, a low-speed-camera-array imaging method for high-speed 3D deformation measurements is proposed. Compared with existing methods using high-speed imaging devices, it has the advantages of low cost and high flexibility achieved by combining low-speed cameras into a stereo camera array high-speed imaging system. In order to achieve accurate 3D measurements, a bundle-adjustment-principle-based system calibration method is proposed. Four experiments, including an accuracy experiment, repeatability experiment, vibration measurement of a plastic board, and out-of-plane displacement measurement of rotating blades, demonstrated the accuracy and effectiveness of the proposed method.





Categories: Optics news

Absolute phase retrieval methods for digital fringe projection profilometry: A review

Optics and Lasers in Engineering - Sun, 04/15/2018 - 06:03
Publication date: August 2018
Source:Optics and Lasers in Engineering, Volume 107

Author(s): Song Zhang

This paper provides a review for absolute phase recovery methods that are applicable for digital fringe projection (DFP) systems. Specifically, we present two conventional absolute phase unwrapping methods: multi-frequency or -wavelength phase-shifting methods, and hybrid binary coding and phase-shifting methods; and also introduce some non-conventional methods that are specific for DFP systems: multiview geometry methods with additional camera(s) or projector(s), DFP system geometric constraint-based phase unwrapping method, and pre-knowledge (e.g., computer-aided-design, CAD, model) based phase unwrapping method. This paper also briefly overviews hybrid methods including phase coding, composite, and pre-defined markers based absolute phase unwrapping methods. This paper explains the principle behind each individual absolute phase unwrapping method; and finally offers some practical tips to handle common phase unwrapping artifact issues.





Categories: Optics news

High-dynamic-range 3D shape measurement utilizing the transitioning state of digital micromirror device

Optics and Lasers in Engineering - Sun, 04/15/2018 - 06:03
Publication date: August 2018
Source:Optics and Lasers in Engineering, Volume 107

Author(s): Vignesh Suresh, Yajun Wang, Beiwen Li

This paper introduces a novel method for 3D shape measurement of high-contrast surfaces in real-time by taking advantage of the transitioning state of digital micromirror device. We propose to project defocused 1-bit binary patterns for sinusoidal generation to bypass the rigid camera-projector synchronization requirement. Each pattern is capture twice in one projection cycle to obtain two fringe images with different brightness: the first fringe is captured when the camera is totally exposed within the projector’s bright period; the second fringe is captured when part of the projector’s dark period is within the camera exposure. The two fringes will be combined to alleviate the saturation problem. Experiments demonstrate the success of the proposed method by showing the real-time 3D shape measurement capability (image acquisition rate: 166 Hz; 3D frame rate: 14 Hz). Moreover, since 1-bit binary patterns are used, it is potentially applicable to high-speed measurements.





Categories: Optics news

A method of the direct measurement of the true stress–strain curve over a large strain range using multi-camera digital image correlation

Optics and Lasers in Engineering - Sun, 04/15/2018 - 06:03
Publication date: August 2018
Source:Optics and Lasers in Engineering, Volume 107

Author(s): Junrui Li, Guobiao Yang, Thorsten Siebert, Ming F. Shi, Lianxiang Yang

A quick method to directly determine the true stress–strain curve over a large strain range is proposed. The true stress–strain curve includes the post-necking strain, is directly measured via a special multi-camera digital image correlation (DIC) system. A tension test with the standard dog-bone shape specimens is used in the system. The cross-section area of the specimen throughout the test is measured by the DIC, as well as the entire field true strain. The true stress is calculated based on the measured cross-section area and the load. A dual-phase steel with a minimum 780 MPa tensile strength (DP780), as a typical advanced high-strength steel (AHSS), is used in the test to demonstrate the method and to validate the result. The true stress–strain curve including the post-necking data of DP780 is presented. The test result is validated with the theoretical calculation as well as the experimental method. Furthermore, the measured true stress–strain curve is approximated by the power law equation to identify the material constants. The methodology, experimental test, and the evaluated result are described in detail.





Categories: Optics news

An optical watermarking scheme with two-layer framework based on computational ghost imaging

Optics and Lasers in Engineering - Sun, 04/15/2018 - 06:03
Publication date: August 2018
Source:Optics and Lasers in Engineering, Volume 107

Author(s): Sui Liansheng, Cheng Yin, Tian Ailing, Anand Krishna Asundi

A two-layer watermarking scheme based on computational ghost imaging and singular value decomposition is proposed. In the first layer, the original watermark is encoded into a significantly small number of measured intensities in the process of computational ghost imaging to constitute a new watermark. In the second layer, the significant blocks chosen from the host image based on spatial frequency are combined to the reference image, which is used to embed the new watermark by using the singular value decomposition. Differing from other watermarking schemes, the information of original watermark can be verified without clear visualization via calculating the nonlinear correlation map between the original one and the reconstructed one. Besides optical parameters such as wavelength and propagation distance, a series of phase-only masks are used as security keys, which can enlarge the key space and enhance the level of security. The results illustrate the feasibility and effectiveness about the proposed watermarking mechanism, which provides an effective alternative for the related work.





Categories: Optics news

A novel CT reconstruction algorithm for incomplete projection based on information repairment

Optics and Lasers in Engineering - Sun, 04/15/2018 - 06:03
Publication date: August 2018
Source:Optics and Lasers in Engineering, Volume 107

Author(s): Yu Xiao, Feng Xu, Kang Shen, Bo Dong, Xiaofang Hu, Tiqiao Xiao

An incomplete projection reconstruction algorithm was proposed in this study. In synchrotron radiation computed tomography (SRCT) of mechanical loading process, shielded projection due to the loading device is the main problem of high-resolution CT reconstruction. Thus, the proposed algorithm was developed based on information repairment considering the continuity of sinogram and slice. The truncated sinogram was estimated using orientation total variation minimization (TVM), which was based on the continuity of projections at adjacent angles in sinogram. Slice rectification was conducted to restrain image distortion, which was based on the continuity of matter contribution. Then, the algorithm was validated by a series of numerical reconstruction experiments. Results showed that the new algorithm could repair the lost boundary and restrain the artifacts. Quantitative comparison of evaluation parameters indicated that the new algorithm worked well when the shielded angle was less than 60° and that satisfactory results could be obtained by approximately 200 times of iteration. Finally, the new algorithm was validated using actual SRCT data and demonstrated effective improvement of reconstruction quality. Therefore, the proposed algorithm may be a suitable method for the in situ SRCT studies of mechanical loading processes.





Categories: Optics news

Influence of no-core fiber on the focusing performance of an ultra-small gradient-index fiber probe

Optics and Lasers in Engineering - Sun, 04/15/2018 - 06:03
Publication date: August 2018
Source:Optics and Lasers in Engineering, Volume 107

Author(s): Shubo Bi, Chi Wang, Jun Zhu, Zhiwen Yuan, Yingjie Yu, Sergiy Valyukh, Anand Asundi

The light-beam expansion effect of a no-core fiber on the focusing performance of an ultra-small gradient-index fiber probe is investigated with a view to optimizing the optical performance of such probes. By taking the variable relationship between the focusing performance (including the working distance and the focusing spot size) of the probe and the length of the no-core fiber as the criterion, the effective beam expansion length of the no-core fiber in the ultra-small gradient-index fiber probe is calculated based on the basic properties of the Gaussian beam. Verification and analysis are done by numerical calculations and experimental measurements, respectively. The obtained results show that the working distance of an ultra-small gradient-index fiber probe can be increased effectively by adding a no-core fiber; however, this will lead to increasing the focusing spot size. For the parameters of the fiber probe studied here, the effective beam expansion length of the no-core fiber spacer is less than 0.357 mm.





Categories: Optics news

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