Hasil untuk "Applied optics. Photonics"

Vindula L. Jayaweera, Chamodi Peiris, Dhanushika Darshani et al.

Underwater wireless communications face significant challenges due to high attenuation, turbulence, and water turbidity. Traditional methods like acoustic and radio frequency (RF) communication suffer from low data rates (<100 kbps), high latency (>1 s), and limited transmission distances (<10 km).Visible Light Communication (VLC) emerges as a promising alternative, offering high-speed data transmission (up to 5 Gbps), low latency (<1 ms), and immunity to electromagnetic interference. This paper provides an in-depth review of underwater VLC, covering fundamental principles, environmental factors (scattering, absorption), and dynamic water properties. We analyze modulation techniques, including adaptive and hybrid schemes (QAM-OFDM achieving 4.92 Gbps over 1.5 m), and demonstrate their superiority over conventional methods. Practical applications—underwater exploration, autonomous vehicle control, and environmental monitoring—are discussed alongside security challenges. Key findings highlight UVLC’s ability to overcome traditional limitations, with experimental results showing 500 Mbps over 150 m using PAM4 modulation. Future research directions include integrating quantum communication and Reconfigurable Intelligent Surfaces (RISs) to further enhance performance, with simulations projecting 40% improved spectral efficiency in turbulent conditions.

Junpeng Zheng, Ruhao Zhao, Cong Zhang et al.

Generalized two-dimensional (2D) Airy beam is a kind of self-accelerating beam with variable initial angle between its two wings, manifested itself as an initial angle determined parabolic trajectory during the free-space propagation. However, the independent and flexible manipulation of both the transverse optical field and longitudinal trajectory of the generalized 2D Airy beam has not been achieved yet which limits its application in the various fields. Herein, we report on tailoring of the propagation properties of the generalized 2D Airy beam based on the catastrophe theory, where analytical expression of its propagation trajectory is derived. In order to clarify the relationship between the transverse optical field distribution and the longitudinal trajectory, we analytically put forward a generation vector, facilitating the tailoring of both longitudinal trajectory and transverse distribution of optical field simultaneously. Consequently, we can effectively generate the generalized 2D Airy beam and precisely manipulate the evolution of its peak intensity. Once the initial and terminal points of trajectory are determined in advance, we can flexibly tailor the trajectory of 2D Airy beam, with the help of corresponding generation vector. Meanwhile, when the longitudinal trajectory is fixed, we can flexibly rotate the transverse optical field distribution of the generalized 2D Airy beam and manipulate its initial angle. Experimental verifications of the manipulation capabilities for the longitudinal trajectory, initial angle, and the rotation of transverse optical field are provided to validate our theoretical results.

M. Cățeanu, S. M. Miclescu

This study evaluates the use of close-range photogrammetry, specifically the Structure-from-Motion (SfM) technique, for assessing road surface deformations. Utilizing a low-cost GoPro Hero 10 action camera, 3D models were created for a 45-meter degraded road section, in order to calculate the volume of road surface defects. Three image collection strategies were compared: only near-nadiral imagery, and near-nadiral plus one or two tracks of oblique images, respectively. Reference data was obtained from Terrestrial Laser Scanning (TLS), in order to assess the level of accuracy for deformation volumes calculated from SfM data. The photogrammetric models, scaled and georeferenced using Ground Control Points (GCPs), allowed for an accurate assessment of deformation volumes (RMSEs of 0.16&ndash;0.18 dm³ for the 32 potholes identified in the studied sector) and road surface reconstruction (with average displacements between SfM and TLS point clouds of 0.007&ndash;0.13 meters). Deformation volumes extracted from SfM 3D models of the road surface are highly correlated with reference volumes from TLS data, regardless of image collection strategy. However, using at least one track of oblique image collection leads to an accuracy improvement. Our findings confirm that close-range photogrammetry with a low-cost, easily available action camera, is an effective, cost-effective alternative for monitoring road deformations, offering high-resolution 3D models suitable for precise volume and depth measurements. However, the technique does have some limitations, mainly related to the need of GCPs in order to scale the 3D models and the significant amount of manual labour necessary in order to calculate the volume of road surface defects.

Berhane Nugusse Zereay, Sándor Kálvin, György Juhász et al.

We developed and applied a new calibration method to make more accurate measurements with our multi-color ellipsometric mapping tool made from cheap parts. Ellipsometry is an optical technique that measures the relative change in the polarization state of the measurement beam induced by reflection from or transmission through a sample. During conventional ellipsometric measurement, the data collection is relatively slow and measures one spot at a time, so mapping needs a long time compared with our new optical mapping equipment made by an ordinary color LED monitor and a polarization-sensitive camera. The angle of incidence and the incident polarization state is varied point by point, so a special optical calibration method is needed. Three SiO₂ samples with different thicknesses were used for the point-by-point determination of the angle of incidence and rho (ρ) corrections. After the calibration, another SiO₂ sample was measured and analyzed using the calibrated corrections; further, this sample was independently measured using a conventional spectroscopic ellipsometer. The difference between the two measured thickness maps is less than 1 nm. Our optical mapping tool made from cheap parts is faster and covers wider area samples relative to conventional ellipsometers, and these correction enhancements further demonstrate its performance.

Victor V. Kotlyar, Alexey A. Kovalev, Alexey M. Telegin

Based on the Richards-Wolf (RW) formalism, we obtain two different exact expressions for the angular momentum (AM) density of light in the focus of an optical vortex with a topological charge <i>n</i> and right circular polarization. One expression for the AM density is derived as the cross product of the position vector and the Poynting vector and has a nonzero value in the focus for an arbitrary integer <i>n</i>. Another expression for the AM density is equal to a sum of the orbital angular momentum (OAM) and the spin angular momentum (SAM) and, in the focus of a considered light field, is equal to zero at <i>n</i> = −1. These expressions are not equal at each point in space, but their 3D integrals are equal. Thus, we derive exact expressions for the AM, SAM and OAM densities in the focus of an optical vortex with right circular polarization and demonstrate that the identity for the densities AM = SAM + OAM is not valid. In addition, we show that the expressions for the strength vectors of the electric and magnetic field near the tight focus, obtained on the basis of the RW formalism, are exact solutions of Maxwell’s equations. Thus, the RW theory exactly describes the behavior of light near the tight focus in free space.

Kai Hu, Ye Zhu, Zhongmin Xu et al.

Free electron laser (FEL) is capable of producing ultra-short X-ray pulses. The estimation of X-ray pulse propagation is the key process of X-ray FEL beamline design. By using the Kostenbauder matrix approach, the evolution of an ultra-short pulse in a beamline system can be calculated. Therefore, it is of significant importance to investigate the Kostenbauder matrices of different kinds of X-ray optics. In this work, we derive a unified 6 × 6 optical matrix to describe various kinds of X-ray optical elements, including varied-line-spacing (VLS) toroidal grating, VLS spherical grating, VLS cylindrical grating, VLS plane grating, toroidal grating, spherical grating, cylindrical grating, plane grating, toroidal mirror, spherical mirror, cylindrical mirror, and plane mirror. These optics are usually adopted in soft X-ray regime. We apply this method to describe the transverse focusing, pulse front tilt, and pulse stretching after an X-ray pulse going through a VLS plane grating monochromator (VLS-PGM). We also use this approach to simulate a grating compressor which can be used to compress chirped soft X-ray pulse. This work is helpful in the design and optimization of X-ray beamline systems.

سیدمحمد حسینی, میلاد کعبی

در این مقاله، ما یک سامانه‌ی درهم‌تنیده دو کیوبیت ابررسانای یکسان را مدل‌سازی می‌کنیم که در آن اتصالات جوزفسون با یک خازن ثابت جفت شده‌اند. این جفت‌شدگی خازن با اتصالات جوزفسون بدلیل افزایش همدوسی و بی اثر کردن اثرات واهمدوسی در سامانه افزوده شده است. برای درک بهتر از حالت سامانه با بهره‌گیری از تئوری محاسبات کوانتومی رفتارهای کیفی درهم‌تنیدگی، همدوسی و مقایسه بین آن‌ها در این مدل بصورت عددی مورد بررسی قرار گرفت. مشاهده شد برای افزایش انرژی جفت‌شدگی بین دو کیوبیت، حدی برقرار است و فراتر از آن باعث تضعیف عملکرد سامانه خواهد شد. همچنین دیده شد رفتارهای درهم‌تنیدگی و همدوسی تقریبا مشابه هستند و می‌توان با راه‌کارهایی آن‌ها را در دماهای بالا حفظ کرد. نکته‌ای قابل توجه این بود که با افزایش انرژی جوزفسون کیوبیت‌ها، همدوسی و درهم‌تنیدگی حتی برای دما‌های بالا نیز افزایش می‌یابد. همچنین با افزایش انرژی جفت‌شدگی متقابل بین کوبیت‌ها، همدوسی و درهم‌تنیدگی در دماهای بالا حفظ می‌شود که می‌توان این نکته را در ساخت منابع درهم‌تنیدگی لحاظ کرد. افزون‌براین، تفاوت بین یک سامانه‌ی با دوکیوبیت همسان و ناهمسان نیز بیان می‌شود.

Ruixiang Qu, Guoqiang Li

Liquid crystals (LCs) are nanophotonic materials which can interact with light in the molecular scale. While the LCs are widely used in various displays, last decade has witnessed emerging applications of the LCs for nondisplays. Based on the unique stimuli–responsive property and optical property, the applications of the LCs in the field of sensors are widely explored. In addition, ions are widely distributed in nature and bionts, playing critical roles in many physiological activities and ecological cycles. Appropriate amount of ions is beneficial to the human body, while the excess ions can cause irreversible damages. As a result, a variety of LC sensors are proposed to detect the ion concentration in both body fluids and water samples. This article reviews the design principles, applications, and existing problems of the LC ion sensors. The geometries, alignments, and optical signals of the sensors, which can guide the design of the devices, are first discussed. Afterward, two types of LC ion sensors aiming at detecting metal ions and nonmetallic ions, respectively, are illustrated. Finally, the current challenges and potential development directions of the LC ion sensors are introduced briefly.

P. Buschinelli, J. D. Salazar, J. D. Salazar et al.

The oil and gas offshore industry demands regular inspections of components and structures that are subjected to extreme operational and environmental conditions. In this context, risers are pipelines that transport mainly oil, gas, water, and cables between submarine structures and the surface offshore platform, in the portion not touching the ocean floor. The emerged part of these risers is typically inspected by industrial climbing, which is a very time-consuming activity, has high operational costs, is dangerous and has a strong dependence on inspector skills. Remotely Piloted Aircraft Systems (RPAS) have been recently used for visual inspection of risers, however, no quantitative or geometrical evaluation has been conducted using this kind of image acquisition yet. An image-based measurement technique, such as close-range photogrammetry, can provide a 3D reconstruction using images, but a series of requisites is mandatory to achieve good results as image acquisition sequence, overlap, camera positioning network, spatial resolution and object texture in non-prepared and targetless scenes. The analysis of different image acquisition strategies using a real RPAS is too difficult because it demands a lot of time, good weather, daylight, and a scene similar to where risers are installed. An alternative is to use simulation. In this paper a ROS/Gazebo simulation is described and used to create a realistic textured 3D virtual environment of the platform, risers and RPA, providing a fast and low-cost solution to simulate different RPA trajectories for photogrammetry image acquisition in targetless scenes. These trajectories are evaluated by comparing the measured risers through photogrammetry to its CAD/simulated model. Since the scene is not prepared, the RPA position/orientation or a stereo vision setup can be used to set scale to the measurement result. The best trajectory found during simulations was also evaluated in a real experiment.

Z. Zhang, C. Wen, Y. Chen et al.

This paper presents a deep learning feature-based method for registration of indoor mobile LiDAR data. Our method is to input point cloud directly, which is more robust to noise than traditional algorithms. The proposed method involves three steps. We first extract the key points by Harris3D algorithm and get their local patches by our sampling method. Second, a Siamese network is trained to describe the patches as local descriptors. Finally, we obtain the final matching pairs depends on the distance which is between two descriptors, and then solve the transformation matrix. The accuracy of registration is within 6&thinsp;cm when the overlap is greater than 35%. In order to improve the registration accuracy, the ICP algorithm is used to fine-tuning the registration results. And the final registration accuracy is within 3.5&thinsp;cm. The experiments show that our method applied to the registration of indoor mobile LiDAR data robustly and accurately.

A. V. Gaboutchian, V. A. Knyaz, V. A. Knyaz

Improvements of existing and development of new non-contact measurement techniques, especially for surfaces of complex spatial shape, allow involvement of various disciplines into advanced technological reality. These improvements have two major directions. The first, being more obvious, refers to introduction of accurate digital 3D images in spheres where real objects have become subjects of traditional study, techniques or manufacturing technologies. The other direction deals with substantial methodological improvements, as they become possible only with introduction of the above-mentioned techniques. Among such is the division of physical anthropology, of dentistry and other disciplines related to dental studies, – odontometry, or measurements of teeth. Traditional odontometry, by turning into automated digital odontometry, becomes a method of accurate and objective morphological assessments in dentistry and anthropology, including palaeoanthropology. As a new method, automated digital odontometry requires interpretations of dental morphology (applicable in digital techniques), accurate 3D images of teeth and software based on 3D and 2D image analysis suitable for automated measurements. The mentioned factors are particularly important for this method due to its inapplicability on real objects. Thus various approaches to obtaining digital images are discussed in the context of their quality and conformity with the studied material and odontometric technique, which currently includes automated orientation algorithms setting locations for principal morphological structures and measurement algorithms themselves, likewise functioning in an automated mode.

hadi Rahimi

In this paper, we explore the linear response of one dimensionalquasiperiodic structure based on Fibonacci sequence composed of silicon dioxide,polystyrene and graphene materials. Here, a graphene monolayer is sandwichedbetween two adjacent layers. The numerical results are obtained by using the standardtransfer matrix method. Due to the presence of graphene sheet in each structure, in theinitial range of THz, an additional gap GPBG is induced which is absent in the case ofwithout graphene. The amplitude of absorption peaks at the upper edge of the GPBGsignificantly enhances, when damping factor increases. The height of the absorptionpeak at the GPBG edge goes up as the temperature increases. At the GPBG edge, withincreasing the thickness of graphene, the absorption peak rises and shifts to the lowerfrequencies. Moreover, we have realized that the amplitude of absorption peaks at theupper edge of the GPBG significantly enhance by increasing damping factor.

Nannan Luan, Lei Zhao, Yudong Lian et al.

A unique surface plasmon resonance (SPR) sensor based on photonic crystal fiber (PCF) is proposed in this paper, which consists of a D-shaped profile where a gold film is coated on its flat surface and a laterally accessible hollow core in which the analyte is infiltrated. The spectral sensitivity and the amplitude sensitivity of the proposed sensor are investigated by the finite element method when it is completely and partly immersed into the analyte solution. Simulation results indicate that the proposed sensor can detect the refractive index of the analyte higher than that of the PCF background, and shows higher sensitivity when its core portion is immersed into the analyte. In this way, this sensor can provide the ability of anti-interference from the metal coating. The proposed sensor can be conveniently coated with metal films and provides a possibility for real time sensing, which are not possible with traditional PCF-based SPR sensors.

Y. Takenaka, M. Katoh, S. Deng et al.

Pine wilt disease is caused by the pine wood nematode (<i>Bursaphelenchus xylophilus</i>) and Japanese pine sawyer (<i>Monochamus alternatus</i>). This study attempted to detect damaged pine trees at different levels using a combination of airborne laser scanning (ALS) data and high-resolution space-borne images. A canopy height model with a resolution of 50&thinsp;cm derived from the ALS data was used for the delineation of tree crowns using the Individual Tree Detection method. Two pan-sharpened images were established using the ortho-rectified images. Next, we analyzed two kinds of intensity-hue-saturation (IHS) images and 18 remote sensing indices (RSI) derived from the pan-sharpened images. The mean and standard deviation of the 2 IHS images, 18 RSI, and 8 bands of the WV-2 and WV-3 images were extracted for each tree crown and were used to classify tree crowns using a support vector machine classifier. Individual tree crowns were assigned to one of nine classes: bare ground, <i>Larix kaempferi</i>, <i>Cryptomeria japonica</i>, <i>Chamaecyparis obtusa</i>, broadleaved trees, healthy pines, and damaged pines at slight, moderate, and heavy levels. The accuracy of the classifications using the WV-2 images ranged from 76.5 to 99.6&thinsp;%, with an overall accuracy of 98.5&thinsp;%. However, the accuracy of the classifications using the WV-3 images ranged from 40.4 to 95.4&thinsp;%, with an overall accuracy of 72&thinsp;%, which suggests poorer accuracy compared to those classes derived from the WV-2 images. This is because the WV-3 images were acquired in October 2016 from an area with low sun, at a low altitude.

Dagong Jia, Yulong Zhang, Zhitong Chen et al.

Quantitatively evaluating the reliability of fiber Bragg grating (FBG) sensor networks becomes problematic as the number of working fiber failures increases in dedicated protection mode. To solve this problem, a signal attenuation rate (SAR) of the sensor system is proposed to evaluate self-healing capabilities after increased working fiber failures. We analyze the influencing factors and calculate the theoretical values of SAR under different network states for values of split ratio a = 0.1, 0.5, and 0.9. Our theoretical model was experimentally demonstrated using an FBG sensor network with four sensors. The results of our calculations using this model agree with our experimental results.

L. Chengfeng, W. Yuan, J. Haoyan et al.

As the birthplace of Yangtze River, the Yellow River and Lancang Rive, Source Region of Three Rivers (SRTR) is an important resource for fresh water supplement in China. SRTR also has very obvious ecological function which forms ecological security barrier for China's Qinghai-Tibet plateau. The inland lakes here play an important role for the water cycle in the plateau. The monitoring results were extracted with TM data from 1976 to 2009. The results show that from 1976 to 2009 the lakes' area in SRTR dropped first and then expanded with 2000 as sector. The lakes area was 6778 km² in 2009, about 1.90% of the whole region, and increased than 1976 by 133.15 km². Most of the large lakes above 80 km2 have the same change trend. The expanded lakes increased in number gradually, while the changes in the amplitude and time characteristics were different. From 1976 to 2000, the number of new lakes increased while died lakes dropped; and from 2000 to 2009 it is just on the contrary. In the study the index of lake change trend (ILCT) was adopted to contrast lake atrophy condition. With ILCT 24.55 there is an expansion trend for the lakes in SRTR during the last 35 years. The lakes with ILCT's absolute value greater than 1 were those merged with or disconnected from surrounding smaller lakes. Here the precipitation and snow melt are main supplies for the lakes. The change of lakes' area has well correlated with precipitation, and weak correlated with temperature from 1976 to 2009. But from 2000 to 2009, there has a strong correlation with precipitation, temperature. All these show from the side that the precipitation and snow melt are important factors to influence the lakes’ change. The lakes have the coordination function for the good ecological environment in the region. The conclusions from the study can provide references in response to climate change research and rational utilization of water resources in SRTR.

C. Stal, R. Goossens, L. Carlier et al.

The Walloon Region in Belgium played a leading role in the world economy and in the industrial sciences and engineering since the 19^th century. Several relicts, such as important industrial buildings or sites, are spread over a large area and are still dominating the current landscape. Some of these remnants are preserved as monuments, representing the industrial, cultural and ecological transition of the region during the last two centuries. Since 2012, UNESCO recognized the importance of four of the best preserved 19^th and 20^th century coal mining sites and classified them as World Heritage ("Major Mining Sites of Wallonia", Le Grand-Hornu, Bois-du- Luc, Le Bois du Cazier and Blegny Mine). The four recognised mining sites together form a strip of about 170 km long, containing important examples of the so-called 'neo classical architecture’ from the early periods of the industrial era in continental Europe. Motivated by this recognition and by the huge touristic and educational potential of the sites, a partnership between the Walloon government and Ghent University was organized. In this first stage, the collaboration focuses on the site of Bois-du-Luc in the municipality of La Louvière, containing a large series of dwellings, several equipments built between 1853 and 1923 by the <i>Société des Charbonnages du Bois-du-Luc</i>, workshops and heaps. Consisting of numerous buildings dating back to the period between 1838 and 1923, this site is one of Europe’s oldest collieries.<br><br> The collaboration between the Walloon government and Ghent University &ndash; Department of Geography fits in the hands-on training which students in land surveying and geomatics receive during their Bachelor studies. For the students it is very interesting that their practical exercises are not limited to the university campus, but that they are involved in a real measurement campaign. The project consists of a series of intensive land surveying campaigns, resulting in highly detailed and accurate maps of the site, including the inside domain of the buildings. Already available aerial photographs are processed to obtain a 3D model of the site and the wider region. In March 2013, the first campaign took place. During this first campaign, a topographical network was set out and a series of detail points were measured for the detailed topographic mapping. The topographical network was well-planned and covers almost the whole site, forming a set of permanently materialized reference points for later measurements. Besides, a large number of ground control points (GCPs) were taken for the 3D reconstruction of the area, based on high resolution airborne imagery. This enables the students to familiarize themselves with photogrammetric principles in a practical exercise. Both the topographic maps and the 3D model fit within the large scale geographic reference map of the Walloon Region.<br><br> In this contribution, the results of this intensive trans-regional collaboration on the preservation of the sites are presented. This paper will discuss the first deliverables from the project and the advantages for the responsible government, the cultural heritage organisations (Ecomusée du Bois-du-Luc) and the students. The main focus here is on the educational context of the project. Furthermore, future projects on the same site will be discussed.

K. Kregar, D. Grigillo, D. Kogoj

Many applications of terrestrial laser scanners (TLS) require the determination of a specific point from a point cloud. In this paper procedure of high precision planar target center acquisition from point cloud is presented. The process is based on an image matching algorithm but before we can deal with raster image to fit a target on it, we need to properly determine the best fitting plane and project points on it. The main emphasis of this paper is in the precision estimation and propagation through the whole procedure which allows us to obtain precision assessment of final results (target center coordinates). Theoretic precision estimations – obtained through the procedure were rather high so we compared them with the empiric precision estimations obtained as standard deviations of results of 60 independently scanned targets. An <i>χ</i>²-test confirmed that theoretic precisions are overestimated. The problem most probably lies in the overestimated precisions of the plane parameters due to vast redundancy of points. However, empirical precisions also confirmed that the proposed procedure can ensure a submillimeter precision level. The algorithm can automatically detect grossly erroneous results to some extent. It can operate when the incidence angles of a laser beam are as high as 80&deg;, which is desirable property if one is going to use planar targets as tie points in scan registration. The proposed algorithm will also contribute to improve TLS calibration procedures.

A. Witayangkurn, M. Nagai, K. Honda et al.

The Unmanned Aerial Vehicle (UAV) is an emerging technology being adapted for a wide range of applications. Real-time monitoring is essential to enhance the effectiveness of UAV applications. Sensor networks are networks constructed from various sensor nodes. International standard such as OGC's SOS (Sensor Observation Service) makes it possible to share sensor data with other systems as well as to provide accessibility to globally distributed users. In this paper, we propose a system combining UAV technology and sensor network technology to use an UAV as a mobile node of sensor network so that the sensor data from UAV is published and shared real-time. A UAV can extend the observation range of a sensor network to remote areas where it is usually difficult to access such as disaster area. We constructed a UAV system using remote-controlled helicopter and various sensors such as GPS, gyrocompass, laser range finder, Digital camera and Thermometer. Furthermore, we extended the Sensor Observation Service (SOS) and Sensor Service Grid (SSG) to support mobile sensor nodes. Then, we conducted experiments of flying the helicopter over an area of the interest. During the flight, the system measured environmental data using its sensors and captured images of the ground. The data was sent to a SOS node as the ground station via Wi-Fi which was published using SSG to give real- time access to globally distributed users.