Hasil untuk "Applied optics. Photonics"

Sergey Kh. Batygov, Liudmila V. Moiseeva, Valeria V. Vinokurova et al.

Ce3+ luminescence was studied in a flurozirconate glass in the ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) and in a fluorohafnate HfF4-BaF2-LaF3-AlF3-NaF (HBLAN) glass systems under X-ray and UV excitation. Ce3+ luminescence temperature quenching in glasses in the temperature range 77–300 K was observed. The Ce3+ luminescence quenching in ZBLAN glass host is conditioned by two mechanisms: via the electrons ionization from the excited 5d-level of Ce3+ into the conduction band (CB); and quenching as a result of the intersection of the Ce3+ ground state and excited state potential curves. In HBLAN glass host the luminescence quenching is caused by the intersection of the Ce3+ ground state and excited state potential curves in the temperature range 77–300 K. The activation energies of Ce3+ luminescence quenching in ZBLAN and HBLAN have been determined.

V. Torrelli, M. C. G. Alasio, M. D'Alessandro et al.

We investigate the robustness of single-mode (SM) emission in high-power, large-area rectangular vertical-cavity surface-emitting lasers (VCSELs), emphasizing the impact of self-heating effects. Compared to circular geometries, large-area rectangular VCSELs provide improved heat dissipation thanks to their high geometrical aspect ratio, and higher SM output power by means of their patterned reflectivity obtainable by an array of grating reliefs. Self-heating alters the refractive index of the device. We demonstrate, experimentally and numerically, how the related thermal lensing affects the transverse modes. By misaligning the antinodes of the promoted lasing mode and the surface reliefs, self-heating degrades SM operation if not properly accounted for in the relief position design. Combining thermal and optical models, we propose numerically optimized grating relief geometries ensuring robust SM emission across varying operating temperatures.

Wenhan Dong, Zeyu Wan, Yun-Cheng Yang et al.

A comparative study is presented on the dependence of optical and material properties of VCSELs on Ge and GaAs substrate thicknesses as well as epitaxy process conditions. It was found that adjusting the Ge substrate thickness and optimizing the epitaxy process can shift the stopband center and cavity resonance wavelength by several nanometers. Ge-based VCSELs exhibit improved epitaxial uniformity, smaller deviations from design specifications, reduced stoichiometry variations, and strain magnitudes comparable to those of GaAs-based counterparts. In the selected 46.92 μm² sample area, no defects were observed in the quantum well (QW) regions of Ge-based VCSELs, and the threading dislocation density (TDD) was measured to be below 2.13 × 10⁶ cm^−2. These results highlight the potential of Ge substrates as promising candidates for advanced VCSELs.

Alexandre Freitas, João Pires

In the original publication [...]

Yunxiu Ma, Gang Zhong, Zhigao Dai et al.

Abstract In-plane hyperbolic phonon polaritons (HPhPs) are phonon-mediated hybrid electromagnetic modes, particularly in two-dimensional (2D) van der Waals (vdW) crystals, which have attracted increasing attention because of their peculiar optical properties and promising nanophotonic applications. Here, we review the most recent advances in in-plane HPhPs in terms of materials, optical properties and nanophotonic devices. We begin with a survey of recently discovered in-plane anisotropic vdW materials and bulk crystals that naturally exhibit in-plane HPhPs. The fundamental properties of HPhPs in these anisotropic materials are then discussed, focusing on propagation directionality such as direction rotation, unidirectional excitation, canalization, negative reflection, and negative refraction. Finally, we discuss the present applications of in-plane HPhPs in nanophotonic devices and offer a perspective on future developments of in-plane HPhPs towards nanophotonic chips.

Wolfhard Oberhausen, Iaroslav Lubianskii, Gerhard Boehm et al.

Terahertz quantum cascade laser sources based on intra-cavity Cherenkov difference-frequency generation in dual-wavelength mid-infrared quantum cascade lasers are currently the only monolithic semiconductor laser technology that can deliver continuous-wave coherent terahertz output at room temperature. Because the Cherenkov difference-frequency generation process enables terahertz radiation generation and extraction across a wide range of frequencies, it is often assumed that phase-matching conditions for this process are automatically fulfilled. We theoretically analyze and experimentally demonstrate that phase-matching plays an important role in these devices, and significant improvements in terahertz power output can be achieved by adjusting the waveguide configuration of the quantum cascade lasers to provide better phase-matching.

C. Gigli, A. Saba, A. B. Ayoub et al.

Deep neural networks trained on physical losses are emerging as promising surrogates for nonlinear numerical solvers. These tools can predict solutions to Maxwell’s equations and compute gradients of output fields with respect to the material and geometrical properties in millisecond times which makes them attractive for inverse design or inverse scattering applications. Here we develop a tunable version of MaxwellNet with respect to incident power, a physics driven neural network able to compute light scattering from inhomogenous media with a size comparable with the incident wavelength in the presence of the optical Kerr effect. MaxwellNet maps the relation between the refractive index and scattered field through a convolutional neural network. We introduce here extra fully connected layers to dynamically adjust the convolutional kernels to take into account the intensity-dependent refractive index of the material. Finally, we provide an example of how this network can be used for the topology optimization of microlenses that is robust to perturbations due to self-focusing.

Yuting Zhou, Qingyu Wang, Zhiqiang Ji et al.

Lithium niobate (LN) is a promising optical material, its micro–nano structures have been applied to fields such as photonic crystals, nonlinear optics, optical waveguides, and so on. At present, lithium niobate structural colors are rarely studied. Although the nanograting structure was researched, it has such large full width at half-maximum (fwhm) that it cannot achieve red, green, or blue pixels or other high-saturation structural colors, thus, its color printing quality is poor. In this paper, we design and simulate lithium niobate nanodisk metasurface resonators (LNNDMRs), which are based on Mie magnetic dipole (MD) and electric dipole (ED) resonances. In addition, the resonators yield very narrow reflection peaks and high reflection efficiencies with over 80%, especially the reflection peaks of red, green, and blue pixels with fwhm around 11 nm, 9 nm, and 6 nm, respectively. Moreover, output colors of different array cells composed of single nanodisk in finite size are displayed, which provides a theoretical basis for their practical applications. Therefore, LNNDMRs pave the way for high-efficiency, compact photonic display devices based on lithium niobate.

Wenkai Chen, Yangsheng Zhong, Gangrong Fu et al.

In biomedical engineering, optics, and photonics, fluorescent silkworm silk has many potential applications, but its complex preparation process and the environmental pollution of corresponding chemical dyeing methods hinder its development. Herein, we provide a green and effective method for fabricating fluorescent silkworm silk with enhanced mechanical properties. Citric acid and urea were selected as raw materials for synthesizing carbon dots (CDs), which were applied as additives of silkworm feed to produce fluorescent silkworm silks by microwave-assisted methods. The results showed that a diet of mulberry leaf with 0.5 wt% CDs was safe for silkworms and did not affect silk yield. CDs rapidly entered silkworms and accumulated in their blood and silk glands. After feeding for 90 min, the silk gland fluorescence appeared prominent. Compared with ordinary silk, the highest elongation at break of the CD-modified silk was 22.24%, and the breaking strength was 28.07 MPa, which were increases of 5.05 and 22.84%, respectively. The CD-modified silk displayed intrinsic blue fluorescence when exposed to a 405 nm laser, exhibited no cytotoxic effect on L929 cells and had excellent cell adhesion. The strategy proposed in this work is not only environmentally friendly but can also produce high-quality fluorescent silk on a large scale.

Wangyu Sun, Xu Qin, Shuyu Wang et al.

A plasmonic based nanocircuit transplants the lumped property of classical electronic circuits to optical frequencies, providing a circuit paradigm for optics and photonics. To broaden the material and frequency selections, the concept of a waveguide metamaterial is applied to design lumped elements by utilizing the waveguide’s structural dispersion to emulate the natural material’s dispersion. Here, as an important application of the physics of waveguide metamaterials, a general type of impedance-matching network directly integrated with a waveguide is investigated for various matching occasions of guided waves, outperforming the classical ones using waveguide membranes. Three representative matching examples are analyzed to validate the feasibility, namely, transmission discontinuities, active power amplifiers, and antennas. The numerical and experimental results confirm the impedance-matching applications of the waveguide metamaterial and suggest the potential merits of low loss and low crosstalk for the proposed waveguide-integrated matching networks in terahertz integrated-circuit designs.

Wei Yan, Yangrui Huang, Luwei Wang et al.

Abstract Due to less light scattering and a better signal-to-noise ratio in deep imaging, two-photon fluorescence microscopy (TPFM) has been widely used in biomedical photonics since its advent. However, optical aberrations degrade the performance of TPFM in terms of the signal intensity and the imaging depth and therefore restrict its application. Here, we introduce adaptive optics based on the genetic algorithm to detect the distorted wavefront of the excitation laser beam and then perform aberration correction to optimize the performance of TPFM. By using a spatial light modulator as the wavefront controller, the correction phase is obtained through a signal feedback loop and a process of natural selection. The experimental results show that the signal intensity and imaging depth of TPFM are improved after aberration correction. Finally, the method was applied to two-photon fluorescence lifetime imaging, which helps to improve the signal-to-noise ratio and the accuracy of lifetime analysis. Furthermore, the method can also be implemented in other experiments, such as three-photon microscopy, light-sheet microscopy, and super-resolution microscopy.

Liang CHEN, Shao-hua YU, Wei HE

This paper defines the connotation of Digital China. Based on the concept of"Five-in-one"put forward by the Party Central Committee, this paper summarizes the construction logic of Digital China Index System from the three levels of macro objectives, strategy quantification and measurement, and puts forward five core indicators, nine main indicators and four sub item index systems of Digital China. At the same time, various types of efficacy functions, weighted factor analysis and cluster analysis are used to carry out dimensionless processing, weighted calculation and data statistical analysis of the basic data of Digital China index system. Finally, we propose some policy suggestions for the construction of Digital China in the future.

Mikhail Dyakonov

G. Sezen, M. Cakir, M. E. Atik et al.

Detecting building façade elements is a crucial problem in computer vision for image interpretation. In Building Information Modeling (BIM) studies, the detection of building façade elements has an important role. BIM is a tool that allows maintaining a digital representation of all aspects of building information; therefore, it will enable the storage of almost any data related to a given structure, regarding its geometric and non-geometric aspects. Façade segmentation was first studied in the 1970s using hand-crafted expertise. Later, detection and segmentation studies emerged based on shapes of objects and parametric rules. With the developing technology, deep learning approaches in object detection studies have intensified. It is obvious that the desired analyses can be performed faster with deep learning approaches. However, deep learning methods require large training data. Algorithms that consider different situations and are suitable for real-world scenarios continue to be developed. The need in this direction continues in the literature. In this study, door and window detection was carried out with deep learning on an original data set. The algorithms used are YOLOv3, YOLOv4, YOLOv5, and Faster R-CNN. Precision, recall and mean average precision (mAP) are used as evaluation metrics. As a result of the study, precision, recall, and mAP values with YOLOv5 were obtained as 0.85, 0.72, and 0.79, respectively. With Faster R-CNN with the lowest performance, precision, recall, and mAP were obtained as 0.54, 0.63, and 0.54, respectively.

Roger Alexander Martínez-Ciro, Francisco Eugenio López-Giraldo, José Martín Luna-Rivera et al.

Indoor positioning systems based on visible light communication (VLC) using white light-emitting diodes (WLEDs) have been widely studied in the literature. In this paper, we present an indoor visible-light positioning (VLP) system based on red–green–blue (RGB) LEDs and a frequency division multiplexing (FDM) scheme. This system combines the functions of an FDM scheme at the transmitters (RGB LEDs) and a received signal strength (RSS) technique to estimate the receiver position. The contribution of this work is two-fold. First, a new VLP system with RGB LEDs is proposed for a multi-cell network. Here, the RGB LEDs allow the exploitation of the chromatic space to transmit the VLP information. In addition, the VLC receiver leverages the responsivity of a single photodiode for estimating the FDM signals in RGB lighting channels. A second contribution is the derivation of an expression to calculate the optical power received by the photodiode for each incident RGB light. To this end, we consider a VLC channel model that includes both line-of-sight (LOS) and non-line-of-sight (NLOS) components. The fast Fourier transform (FFT) estimates the powers and frequencies of the received FDM signal. The receiver uses these optical signal powers in the RSS-based localization application to calculate the Euclidean distances and the frequencies for the RGB LED position. Subsequently, the receiver’s location is estimated using the Euclidean distances and RGB LED positions via a trilateration algorithm. Finally, Monte Carlo simulations are performed to evaluate the error performance of the proposed VLP system in a multi-cell scenario. The results show a high positioning accuracy performance for different color points. The average positioning error for all chromatic points was less than 2.2 cm. These results suggest that the analyzed VLP system could be used in application scenarios where white light balance or luminaire color planning are also the goals.

M. Chambonneau, M. Blothe, Q. Li et al.

M. Chambonneau,1,∗ M. Blothe, Q. Li, V. Yu. Fedorov, T. Heuermann, M. Gebhardt, C. Gaida, S. Tertelmann, F. Sotier, J. Limpert, S. Tzortzakis, S. Nolte Institute of Applied Physics, Abbe Center of Photonics, Friedrich-Schiller-University Jena, Albert-Einstein-Straße 15, 07745 Jena, Germany. Science Program, Texas A&M University at Qatar, P.O. Box 23874, Doha, Qatar. P. N. Lebedev Physical Institute of the Russian Academy of Sciences, 53 Leninskiy Prospekt, 119991 Moscow, Russia. Helmholtz-Institute Jena, Fröbelstieg 3, 07743 Jena, Germany. Active Fiber Systems GmbH, Ernst-Ruska-Ring 17, 07745 Jena, Germany. Innolas Photonics GmbH, Justus-von-Liebig-Ring 8, 82152 Krailling, Germany. Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Center of Excellence in Photonics, Albert-Einstein-Straße 7, 07745 Jena, Germany. Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology—Hellas (FORTH), P.O. Box 1527, GR-71110 Heraklion, Greece. Materials Science and Technology Department, University of Crete, 71003 Heraklion, Greece. *maxime.chambonneau@hotmail.fr (Dated: April 27, 2021)

Mohit Kumar, Pawan Kumar, Andres Vega et al.

X iv :2 11 0. 01 51 1v 1 [ ph ys ic s. op tic s] 4 O ct 2 02 1 Mid-Infrared Photon-Pair Generation in AgGaS2 Mohit Kumar, a) Pawan Kumar, Andres Vega, Maximilian A. Weissflog, 2 Thomas Pertsch, 2, 3 and Frank Setzpfandt Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University Jena, Albert-Einstein-Str. 15, 07745 Jena, Germany Max Planck School of Photonics, Albert-Einstein-Str. 6, 07745 Jena, Germany Fraunhofer Institute for Applied Optics and Precision Engineering, Albert-Einstein-Str. 7, 07745 Jena, Germany

A. Goldberg, M. Grassl, G. Leuchs et al.

Aaron Z. Goldberg,1, 2 Markus Grassl,3, 4 Gerd Leuchs,4, 5, 6 and Luis L. Sánchez-Soto4, 7 1National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada 2Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ontario, M5S 1A7, Canada 3International Centre for Theory of Quantum Technologies, University of Gdańsk, 80-308 Gdańsk, Poland 4Max-Planck-Institut für die Physik des Lichts, 91058 Erlangen, Germany 5Institute of Optics, Information and Photonics, University of Erlangen-Nuremberg, 91058 Erlangen, Germany 6Institute of Applied Physics, Russian Academy of Sciences, 603950 Nizhny Novgorod, Russia 7Departamento de Óptica, Facultad de Física, Universidad Complutense, 28040 Madrid, Spain

Haider Zia

We show theoretically and numerically how to optimize sign-alternating dispersion waveguides for maximum nonlinear pulse compression, while leveraging the substantial increase in bandwidth-to-input peak power advantage of these structures. We find that the spectral phase can converge to a parabolic profile independent of uncompensated higher-order dispersion. The combination of an easy to compress phase spectrum, with low input power requirements, then makes sign-alternating dispersion a scheme for high-quality nonlinear pulse compression that does not require high powered lasers, which is beneficial for instance in integrated photonic circuits. We also show a new nonlinear compression regime and soliton shaping dynamic only seen in sign-alternating dispersion waveguides. Through an example SiN-based integrated waveguide, we show that the dynamic enables the attainment of compression to two optical cycles at a pulse energy of 100 pJ which surpasses the compression achieved using similar parameters for a current state-of-the-art SiN system.

A. S. Kents, Y. A. Hamad, K. V. Simonov et al.

In recent years computed tomography of the lungs has been the most common diagnostic procedure aimed at detection of the pathological changes associated with COVID-19. The study is aimed at the use of the developed algorithmic support in combination with texture (geometric) analysis to highlight a number of indicators characterizing the clinical state of the object of interest. Processing is aimed at the solution of a number of diagnostic tasks such as highlighting and contrasting the objects of interest, taking into account the color coding. Further, an assessment is performed according to the appropriate criteria in order to find out the nature of the changes and increase both the visualization of pathological changes and the accuracy of the X-ray diagnostic report. For these purposes, it is proposed to use preprocessing algorithms for a series of images in dynamics. Segmentation of the lungs and areas of possible pathology are performed using wavelet transform and Otsu threshold value. Delta-maps and maps obtained using Shearlet transform with contrasting color coding are used as a means of visualization and selection of features (markers). The analysis of the experimental and clinical material carried out in the work shows the effectiveness of the proposed combination of methods for studying of the variability of the internal geometric features (markers) of the object of interest in the images.