Optical Principles Research Articles

Assessment of Brain Cortical Activation in Passive Movement During Wrist Task Using Functional Near Infrared Spectroscopy (fNIRS)

Purpose: Nowadays, the number of people diagnosed with movement disorders is increasing. Therefore, the evaluation of brain activity during motor task performance has attracted the attention of researchers in recent years. Functional Near-Infrared Spectroscopy (fNIRS) is a useful method that measures hemodynamic changes in the brain cortex based on optical principles. The purpose of this study was to evaluate the brain’s cortical activation in passive movement of the wrist. Materials and Methods: In current study, the activation of the brain's motor cortex during passive movement of the right wrist was investigated. To perform this study, ten healthy young right-handed volunteers were chosen. The required data were collected using a commercial 48-channel continuous wave fNIRS machine, using two different wavelengths of 765 and 855 nm at 10 Hz sampling rate. Results: Analysis of collected data showed that the brain's motor cortex during passive motion was significantly activated (p≤0.05) compared to rest. Motor cortex activation patterns depending on passive movement direction were separated. In different directions of wrist movement, the maximum activation was recorded at the primary motor cortex (M1). Conclusion: The present study has investigated the ability of fNIRS to evaluate cortical activation during passive movement of the wrist. Analysis of recording signals showed that different directions of movement have specific activation patterns in the motor cortex.

New Trends in Telecommunication

This is the new trend of different wires used in telecommunication like fiber optic and copper wire This study includes various parameters for comparison. For fabrication of any telecommunication, every wire play important role. A pair of Fiber can carry over eight thousand simultaneously voice channels. This paper gives us the idea of high immunity to electromagnetic interference for optical fiber and copper wire. According to this we will explain about Optical Fiber, type, features, theory and principles. Different specification and features of optical fiber cables are also studied. Optical Fiber’s linear features are wavelength window, bandwidth, attenuation and dispersion. Non-linear features are fiber manufacturing, geometry etc. Copper cable has different types such as: Coaxial cable and twisted cable.

A three-dimensional ring-array concentrator solar furnace

A single ring-array concentrator solar furnace unit was firstly modeled analytically, and then optimized numerically by ZEMAX® and ANSYS® software, reaching a temperature of 3778 K, nearly equivalent to that of a medium size solar furnace with 3.14 m2 collection area. A novel three-dimensional ring array concentrator solar furnace was subsequently proposed and analyzed. It consisted of five single ring array concentrators, forming a compact box-shaped solar furnace with an opening at the rear side for an easy access to a common focal spot in the center. Based on the edge-ray principle of non-imaging optics, 30,960 solar concentration ratio was analytically calculated for this solar furnace, leading to significantly enhanced thermal and optical efficiencies. The temperature performance of the three-dimensional ring-array concentrator furnace as a function of receiver size and collector area was analyzed numerically and compared to that of the medium size solar furnace. For a 5.68 mm diameter spherical receiver and large collection area varying from 3.14 m2 to 100 m2, 1.1 times gradual enhancement in the maximum attainable temperature was calculated for the ring array concentrator furnace. More importantly, its average and minimum temperatures were significantly improved by 870 K and 1140 K, respectively, as compared to that of the medium size solar furnace. In addition, the three-dimensional ring-array concentrator also presented a significant tracking error compensation capacity in relation to that with the medium size solar furnace.

Color image encryption based on vector decomposition operations and secondary image phase masks

This paper presents a method aimed at encrypting color images using vector operations and secondary image phase masks (SPMs). In this encryption, the optical coherent superposition principle is used to separate and overlay the original image into two phase plates on the three channels R, G and B, respectively. Then the double random phase encoding in the Fresnel domain is performed using the SPMs to encrypt one of the phase plates. Finally, the Kronecker product of two random matrices is directly perform randomization on the encoded image, achieving multilevel encryption of color images. Computer simulations are presented to demonstrate its performance, and the feasibility and security of the proposed system are analyzed as well.

Generating uniform irradiance in the Fresnel region by quasi-optical beam shaping of a millimeter-wave source.

In this paper, we report on the design, simulation and measurement of a flat-top beam shaper (FBS) lens for a millimeter-wave (mm-wave) antenna coupled source. The beam shaper is designed to transform the pseudo-Gaussian beam of the mm-wave source into a flat-top beam of sharp roll-off at a specific distance in the Fresnel region. Firstly, relying on the geometrical optics principles, we propose an analytical formulation for the design of lens profiles. Next, a simple optimization method based on the full-wave simulation of the lens and the mm-wave antenna is suggested to tune the analytically extracted lens profile. The optimized lens profile is then studied to assess its performance sensitivity to various deviations. Finally, a prototype of the proposed FBS lens is fabricated and measured. As an example study, the radiated beam of a 100GHz conical horn antenna is shaped into a flat-top beam of radius 40 cm with a sharp skirt and low ripples at the distance of 3 meters. The radius of the generated flat-top beam is also shown to be easily tunable by displacing the FBS lens with respect to the horn antenna. The proposed procedure for the design of FBS lens results in a high-quality flat-top beam, which is promising for the applications where a uniform irradiance within the field-of-view with negligible spillover is of high importance. Terahertz (THz) and mm-wave imaging systems are potential candidates in this regard.

Optic flow cues help explain altitude control over sea in freely flying gulls.

For studies of how birds control their altitude, seabirds are of particular interest because they forage offshore where the visual environment can be simply modelled by a flat world textured by waves then generating only ventral visual cues. This study suggests that optic flow, i.e. the rate at which the sea moves across the eye's retina, can explain gulls' altitude control over seas. In particular, a new flight model that includes both energy and optical invariants helps explain the gulls' trajectories during offshore takeoff and cruising flight. A linear mixed model applied to 352 flights from 16 individual lesser black backed gulls (Larus fuscus) revealed a statistically significant optic flow set-point of ca 25° s-1. Thereafter, an optic flow-based flight model was applied to 18 offshore takeoff flights from nine individual gulls. By introducing an upper limit in climb rate on the elevation dynamics, coupled with an optic flow set-point, the predicted altitude gives an optimized fit factor value of 63% on average (30-83% in range) with respect to the GPS data. We conclude that the optic flow regulation principle helps gulls to adjust their altitude over sea without having to directly measure their current altitude.

An efficient off-axis multi-pass Nd:glass amplifier utilizing a birefringence crystal

In this paper we propose an efficient off-axis multi-pass Nd:glass amplifier with a birefringence crystal. By utilizing the optical principle of birefringence crystals and the angle differences of the input–output laser directions in a typical off-axis amplifier, the amplification-pass was extended from four-pass to eight-pass without increasing the off-axis angle. The detailed principles and amplifier parameter design are presented. Using the proposed off-axis eight-pass amplifier, a 1 Hz repetitive Nd:glass amplifier at several joules was experimentally demonstrated. A total transmission of 54% was achieved. At an input energy of 1.5 mJ and small-signal gain of 3.6, the output energy and the corresponding net gain were 2.5 J and 1667, respectively. The beam quality was good. The spatial intensity modulation index for 90% beam aperture was 1.29 and the 95% energy concentration of far field patterns was 2.77 times the diffraction limit.

Sectorial perturbation of vortex beams: Shannon entropy, orbital angular momentum and topological charge

Transformations of the vortex beams structure subjected to sectorial perturbation were theoretically and experimentally studied. The analysis was based on computing (measuring) the vortex spectrum that enables us to find the orbital angular momentum (OAM) and Shannon entropy (informational entropy). We have revealed that, in the general case, the number of vortices caused by an external perturbation is not related to the topological charge. For arbitrary perturbation, the topological charge remains equal to the initial topological charge of the unperturbed vortex beam. Growth of the vortex number induced by perturbations is associated with the optical uncertainty principle between the sectorial angle and the OAM. The computer simulation has shown that OAM does not depend on the number of vortices induced by perturbations. Moreover, two maxima are formed both in the positive and negative regions of the vortex spectrum. As a result, the OAM does not practically change in a wide range of perturbation angles from 0 to 90 °. However, at large perturbation angles, when the energy is almost equally redistributed between the vortex modes with opposite signs of the topological charge, the OAM rapidly decreases. At the same time, the Shannon entropy monotonically increases with growing perturbation angle. This is due to the fact that the entropy depends only on the number of vortex states caused by external perturbations.

Optical Control System for Displacement Monitoring of the High Precision Measurement Setup Elements

Introduction. It is necessary to ensure the reliability of measurements when operating high-precision measurement setups. The elements displacement of the measurement path introduces measurement results distortions, especially in measurement setups operating in the microwave range. It is necessary to monitor the elements positions of the measurement setup to ensure the measurements reliability. The monitoring should be performed during the measurement, and the control device should be connected to the automatic control system of the measurement setup, and it should neither mechanically affect the setup elements nor introduce the electrical and electromagnetic interferences.Objective. The objective of the present work is a design of the control system, which allows monitoring of elements displacements of the high precision measuring setup with an accuracy of 1.0·10–4 mm. And the designed control system should neither mechanically affect the controlled elements nor introduce the electrical and electromagnetic interferences, thus allowing the digital signal processing.Materials and methods. The designed system utilizes optical methods of the displacements monitoring, which are based on the geometric optics principles. The charge-coupled devices (CCD) to record the system response to optical path changes are used.Results. Two designs of the control system for the displacement monitoring of the high precision measurement setup elements are presented. The first system design allows detecting the elements displacement occurrence, and the second system design allows to identify the displaced element. The system is capable to register the elements displacements with accuracy of 1.0·10–4 mm and monitor the elements positions while vibration exposures. The system does not mechanically or electromagnetically affect the controlled elements. All system elements are resistant to the microwave radiation and increased background radiation, excluding CCD that should be placed outside the active zone. The mathematical simulation allows assessing the sensitivity of the designed optical control system. The system sensitivity increasing method by the optical path increasing and corrective reflector using is proposed.Conclusion. The designed control system for the displacements monitoring of the high precision measurement setup elements meets the requirements imposed on it. The system allows the digital signal processing and can withstand the increased microwave, X-ray and background radiation. The designed system is much simpler to implement in comparison with systems based on other physical principles. The novelty of the control system technical solution is confirmed by the patent.

Tactile Sensors for Advanced Intelligent Systems

With the capability of completing a task or achieving a goal in an uncertain environment while simultaneously having the characteristics of adaptability, self‐optimization, self‐diagnostics, and self‐maintenance, intelligent systems have witnessed extraordinary progress in recent years. These advances involve robotics, artificial intelligence and machine learning, automation, human–machine interfaces, the Internet of Things, control theory and control systems, smart and responsive materials, intelligent sensing systems, and programmed self‐assembly. As an active technology conveying mechanical stimuli to a wide range of electrical and optical signals, tactile sensors are essential elements of intelligent systems and have accelerated the emergence of advanced intelligent systems by enabling the accurate recognition and safe interaction of humans and machines, smart sensing of control systems, precise control of robotics, and synergetic work of artificial intelligent systems. Herein, the recent advances of tactile sensors for advanced intelligent systems are reviewed, emphasizing these with the working principles of piezoresistance, resistance, capacitance, piezoelectricity, triboelectricity, and optics. Representative examples of their applications in advanced intelligent systems, such as robotics, human–machine interfaces, and artificial intelligence, are explored. The remaining challenges and perspectives in this emerging field are also discussed.

CONDENSING LENS ON BINOCULAR INDIRECT OPHTHALMOSCOPY AND SLIT-LAMP BIOMICROSCOPY

Condensing lens is a lens used as an auxiliary lens in indirect instruments to examines the fundus. This lens is used with binocular indirect ophthalmoscope and slit-lamp biomicroscope to reach a stereopsis image of fundus. Optical principle of condensing lens is to make the eye in myopic condition, so it can producesa real, aerial, inverted and reversed image. This lens was placed between the instruments and the eye of the patient which located closer to patient’s eye. Optimalized position of the lens can produce a good fundus image.
 Condensing lens have so many power of dioptre that each power produces different magnification and field of view. High powered lenses produces wider field of view than low powered ones. High powered lens can also used in patient with small dilated pupil and shorter distance of examination. Low powered lenses offer more magnification.
 Fundus examination with binocular indirect ophthalmoscope and slit-lamp biomicroscope have purpose to produces stereopsis image because of the binocularity system. These two instruments have each advantages and disadvantages. The advantages of binocular indirect ophthalmoscope are a portable instrument, relatively can be used in uncooperative patient and it can be used with scleral indentation to reach more peripheral view of the fundus. Meanwhile slit-lamp biomicroscope has the advantages to offer more magnification and flexible illumination system. With higher powered lens use in biomicroscope, it also give advantages in shorter distance of examination and wider field of view.

Research on the inner bore profile detecting system of railgun

In the process of electromagnetic launching, there is much inner damage containing wear, corrosion, gouging, and transition in the rail. After several launchings, the damage has an enormous influence on the accuracy of launching and rail lifetime. In order to protect the rail and research on the damage mechanism, this paper provides an insight into the methods of measuring the inner bore of the electromagnetic rail launcher based on the optical vision measurement principle. Applying this optical method, the apparatus is designed and divided into three subsystems. These three subsystems provide global alignment information, the axial depth information, and inner surface profile information respectively. In this way, the 3D model of the rail can be precisely rebuilt. The feasibility of the method was confirmed in the experiment. And this method may have significant implications for the further research on the on-line measurement of electromagnetic rail launchers.

Illumination estimation for augmented reality based on a global illumination model

With the rapid development of 3D technology, the illumination consistency plays an important role in realistic rendering of virtual objects which are superimposed into the real scene. In this paper we proposed a new approach to estimate illumination, given the images of a scene. Our algorithm is designed from principles in optics, which is based on a global illumination model. First, we get the images of a scene and perform scene reconstruction using images. Then, a photon emission hemispherical model is built for emitting photons into the scene. The photons are traced, meanwhile the result is stored in multiple photon maps. Finally, the estimated illumination is obtained by estimating the photon radiance value in the photon emission hemispherical model. Experiments on our newly collected real scene databases and virtual scene databases show the accuracy of our method subjectively and objectively. By comparing with related work, it is found that more accurate results can be obtained using the global illumination inversely.

Optical Principles in Three-Dimensional Vitreoretinal Surgery and Laser Eyewear

Abstract This report analyzed the effect of laser protective eyewear on light polarization and three dimensional (3-D) vision using the Ngenuity 3-D visualization system.

The Micro Solar Flare Apparatus (MiSolFA) instrument concept

The Micro Solar-Flare Apparatus (MiSolFA) is a compact X-ray imaging spectrometer designed for a small 6U micro-satellite. As a relatively inexpensive yet capable Earth-orbiting instrument, MiSolFA is designed to image the high-energy regions of solar flares from a different perspective than that of Solar Orbiter’s STIX, operating from a highly elliptical heliocentric orbit. Two instruments working together in this way would provide a 3-dimensional view of X-ray emitting regions and can bypass the dynamic range limitation preventing simultaneous coronal and chromospheric imaging. Stereoscopic X-ray observations would also contain valuable information about the anisotropy of the flare-accelerated electron distribution. To perform these types of observations, MiSolFA must be capable of imaging sources with energies between 10 and 100 keV, with 10 arcsec angular resolution.MiSolFA’s Imager will be the most compact X-ray imaging spectrometer in space. Scaling down the volume by a factor of ten from previous instrument designs requires special considerations. Here we present the design principles of the MiSolFA X-ray optics, discuss the necessary compromises, and evaluate the performance of the Engineering Model.

NanoCarb hyperspectral sensor: on performance optimization and analysis for greenhouse gas monitoring from a constellation of small satellites

NanoCarb is an innovative Fourier-transform imaging spectrometer dedicated to the measurement of CO2 and CH4. Both its unusual optical principle and sampling strategy allow to reach a compact design, ideal for small satellite constellation as investigated by the European project SCARBO. The NanoCarb performance assessment as well as a proof of concept is required in this framework. We have developed a design strategy to optimize the performances. We demonstrate the potential of the concept through an estimation of the sensitivity, compliant with the space mission target. We also present a preliminary mitigation of the bias induced by water on CO2 and CH4 retrieval, illustrating the efficiency and the flexibility of the NanoCarb partial interferogram sampling technique. The presented design reaches a sub-ppm random error for CO2 and sub-10 ppb random error for CH4, considering 128 km swath and 2 by 2 km2 ground resolution. Design optimization and more systematic performances are discussed.

Objective burn depth assessment of hand burns

The depth assessment of thermal wounds is subject to many variables. Therefore, technical systems are increasingly being used to determine severity. Particularly hand burns can have clinically relevant consequences in terms of function and aesthetic appearance. Hence, a secure assessment for an adequate treatment is necessary.Technical analyzes such as Hyperspectral Imaging, Laser-Doppler-Imaging or Laser-Speckle-Imaging are intended to simplify and objectify the examination by helping to determine the necessary depth of necrectomy and thus to define the skin transplantation area. Furthermore, the diverse technical devices are to improve the functional result, reduce the severity of scarring and cosmetic complaints, and facilitate the evaluation of inexperienced personnel in the field of burn medicine.Therefore, various technical approaches have been pursued, which are largely based on optical principles. The respective devices are not yet used in the standard diagnosis of burn wounds.In future studies it will be necessary to determine an algorithm for the measurement intervals based on the wound dynamics and to evaluate which methodology is superior to the specificity and sensitivity.

Directionally-Unbiased Unitary Optical Devices in Discrete-Time Quantum Walks

The optical beam splitter is a widely-used device in photonics-based quantum information processing. Specifically, linear optical networks demand large numbers of beam splitters for unitary matrix realization. This requirement comes from the beam splitter property that a photon cannot go back out of the input ports, which we call “directionally-biased”. Because of this property, higher dimensional information processing tasks suffer from rapid device resource growth when beam splitters are used in a feed-forward manner. Directionally-unbiased linear-optical devices have been introduced recently to eliminate the directional bias, greatly reducing the numbers of required beam splitters when implementing complicated tasks. Analysis of some originally directional optical devices and basic principles of their conversion into directionally-unbiased systems form the base of this paper. Photonic quantum walk implementations are investigated as a main application of the use of directionally-unbiased systems. Several quantum walk procedures executed on graph networks constructed using directionally-unbiased nodes are discussed. A significant savings in hardware and other required resources when compared with traditional directionally-biased beam-splitter-based optical networks is demonstrated.

Generalized Veselago-Pendry lenses via complex transformation optics.

Field solutions for a conventional Veselago-Pendry (VP) flat lens with ϵ=-ϵ 0 and μ=-μ 0 can be derived based on transformation optics (TO) principles. The TO viewpoint makes it clear that perfect imaging by a VP lens is a consequence of multivalued nature of the particular coordinate transformation involved. This transformation is equivalent to a "space folding" whereby one point in the transformed domain (source point) is mapped to three different points in the physical domain (the original source point plus two focal points). In theory, a VP lens would enable the recovery of the entire range of spectral components, i.e. both propagating and evanescent fields, thus characterizing a "perfect lens". Such lens, if lossess, is indeed "perfect" for monochromatic waves; however, for any realistic wave packet the space folding interpretation provided by TO makes it clear that a VP lens violates primitive causality constraints, which precludes any practical realization. Here, we utilize complex transformation optics (CTO) to derive generalized Veselago-Pendry (GVP) lenses without requiring a multivalued transformation. Unlike the conventional VP lens, the proposed lenses can fully recover the evanescent spectra under more general conditions that include the presence of (anisotropic) material loss/gain.

Optical Imaging of Brain Motor Cortex Activation During Wrist Movement Using Functional Near-Infrared Spectroscopy (fNIRS)

Background: Optical imaging has attracted the researcher’s attention in recent years as an uncompromising and efficient method to measure the changes in brain cortex activity. Functional Near-Infrared Spectroscopy (fNIRS) is a method that measures hemodynamic changes in the brain cerebral cortex based on optical principles. Objectives: The current study aimed to evaluate the activities of the brain cortex during wrist movement using fNIRS. Methods: In this study, the activity of the brain motor cortex was investigated during right wrist movement in 10 young right-handed volunteers. Data were collected using a 48-channel fNIRS device with two wavelengths of 855 nm and 765 nm. For this experiment, 20 channels were used and the sampling frequency was set at 10 Hz. Results: Signal intensity in the motor cortex was significantly higher during movement than in the rest (P ≤ 0.05). The activation map of wrist movements was separated spatially in the motor cortex. The highest activity was recorded in the primary motor cortex (M1). There was a significant difference in the focus of the maximum activation of the brain between the four main directions. Conclusions: It is possible to differentiate between different directions of movement using near-infrared signals. The presence of directional activation in the cerebral cortex helps confirm the notion that this part of the brain participates in the processing of complex information besides controlling the movement of different parts of the body.