Hasil untuk "Applied optics. Photonics"

Yi He, Tao Li, Ruidan Zhu et al.

Studying heat conduction in semiconductors at the micro/nano scale is crucial for further optimizing heat dissipation of electronics. Transient thermal grating (TTG) is a noncontact technique for investigating thermal transport properties of semiconductors. The traditional scheme to extract the thermal diffusivity from the TTG measurements is based on the diffusion equation. At length scales comparable to or even shorter than the mean free paths (MFPs) of phonons, this framework breaks down. Although previous work has proposed a method of theoretical analysis for multidimensional quasi-ballistic thermal transport of phonons in TTG with an analytic solution to the Boltzmann transport equation (BTE), the feasibility of applying this solution to TTG measurements to extract the contribution of phonons to heat conduction has not been tested experimentally. In this work, we selected germanium as the demonstration material and extracted the contribution of phonons with various MFPs to heat conduction successfully based on the TTG experiment data and the solution to the 2-dimensional (2D) BTE. This work not only verifies the viability of this method but also provides an important guide for future research on micro/nano scale heat conduction in semiconductors.

J. Y. Chin, T. Steinle, T. Wehlus et al.

Light propagation is usually reciprocal. However, a static magnetic field along the propagation direction can break the time-reversal symmetry in the presence of magneto-optical materials. The Faraday effect in magneto-optical materials rotates the polarization plane of light, and when light travels backward the polarization is further rotated. This is applied in optical isolators, which are of crucial importance in optical systems. Faraday isolators are typically bulky due to the weak Faraday effect of available magneto-optical materials. The growing research endeavour in integrated optics demands thin-film Faraday rotators and enhancement of the Faraday effect. Here, we report significant enhancement of Faraday rotation by hybridizing plasmonics with magneto-optics. By fabricating plasmonic nanostructures on laser-deposited magneto-optical thin films, Faraday rotation is enhanced by one order of magnitude in our experiment, while high transparency is maintained. We elucidate the enhanced Faraday effect by the interplay between plasmons and different photonic waveguide modes in our system. The Faraday effect rotates the polarization plane of light in magneto-optical materials and is used for optical isolators blocking unwanted backscattering of light. Usually a small effect, Chin et al. have observed a large enhancement of the optical rotation by magneto-plasmonics.

Min Lin, Qing Liu, Huigao Duan et al.

Topological spin textures, among which skyrmions and merons are typical examples, have with their swirling vectorial structures triggered enormous interest in physical systems including elementary particles and magnetic materials. Manipulating their symmetry and topology is important for understanding the mechanisms that underlie their topological phase transformation as well as offering tunable degrees of freedom to encode information, which has already been demonstrated in magnetic materials. Recently, the photonic counterparts of skyrmions and merons were constructed in a 2D wave system with deep-subwavelength features promising for optical sensing, imaging, and information decoding. However, their experimental realization relied on stringent excitation conditions that only support a single spin texture type on a specific structure. Here, we demonstrate for the first time the transformation between photonic skyrmion and meron spin lattices on the same metallic meta-surface having a well-designed structural period. We show experimentally the wavelength-tuned symmetry transformation of the photonic spin lattices, which are also found to be robust against disorder in the structure to a certain degree. This work provides new insights into controlling the electromagnetic field symmetry and topology, as well as in developing applications in spin optics and topological photonics.

Wu Zhou, Kaihang Lu, Shijie Kang et al.

Two-dimensional (2D) diffraction gratings offer a polarization-independent coupling solution between the planar photonic chips and optical fibers, with advantages including placement flexibility, ease of fabrication, and tolerance to alignment errors. In this work, we first proposed and experimentally demonstrated a highly efficient 2D grating coupler enabled by exciting multipolar resonances through bi-level dielectric structures. A 70-nm shallow-etched hole array and a 160-nm-thick deposited polycrystalline silicon tooth array are employed in our proposed 2D grating coupler. Strong optical field confinement and enhanced radiation directionality can thus be attained through the use of 193-nm deep-ultraviolet (DUV) lithography, which is readily accessible from commercial silicon photonics foundries. The measured experimental peak coupling efficiency is -2.54 dB with a minimum feature size of 180 nm. Our design exhibits a 3-dB bandwidth of around 23.4 nm with good positioning tolerance for optical fibers. Due to the benefits of perfectly vertical coupling, the measured polarization-dependent loss in our experiments is below 0.3 dB within the 3-dB working bandwidth. Our proposed 2D grating structure and design method can also be applied to other integrated optics platforms, enabling an efficient and polarization-diversity coupling between optical fibers and photonic chips while reducing requirements on feature size.

Duy-Anh Nguyen, Dae Hee Kim, Geon Ho Lee et al.

Abstract Surface plasmon resonance (SPR) sensors are based on photon-excited surface charge density oscillations confined at metal-dielectric interfaces, which makes them highly sensitive to biological or chemical molecular bindings to functional metallic surfaces. Metal nanostructures further concentrate surface plasmons into a smaller area than the diffraction limit, thus strengthening photon-sample interactions. However, plasmonic sensors based on intensity detection provide limited resolution with long acquisition time owing to their high vulnerability to environmental and instrumental noises. Here, we demonstrate fast and precise detection of noble gas dynamics at single molecular resolution via frequency-comb-referenced plasmonic phase spectroscopy. The photon-sample interaction was enhanced by a factor of 3,852 than the physical sample thickness owing to plasmon resonance and thermophoresis-assisted optical confinement effects. By utilizing a sharp plasmonic phase slope and a high heterodyne information carrier, a small atomic-density modulation was clearly resolved at 5 Hz with a resolution of 0.06 Ar atoms per nano-hole (in 10–11 RIU) in Allan deviation at 0.2 s; a faster motion up to 200 Hz was clearly resolved. This fast and precise sensing technique can enable the in-depth analysis of fast fluid dynamics with the utmost resolution for a better understanding of biomedical, chemical, and physical events and interactions.

M. A. Khalili, L. Guerriero, M. Pouralizadeh et al.

Around the world, the occurrence of landslides has become one of the greatest threats to human life, property, infrastructure, and natural environments. Despite extensive research and discussions on the spatiotemporal dependence of landslide displacements, there is still a lack of understanding concerning the factors that appear to control displacement distribution in landslides because of their significant variations. This paper implements a Graph Convolutional Network (GCN) to predict displacement following the Moio della Civitella landslide in southern Italy and identify factors that may affect the distribution of movement following the landslide. An interferometric technique, known as permanent scatter interferometry (PSI), has been developed based on Synthetic Aperture Radar (SAR) satellite imagery to derive permanent scatter points that can be used to represent the deformation of landslides. This study utilized the GCN regression model applied to PSs points and data reflecting geological and geomorphological factors to extract the interdependency between paired data points, resulting in an adjacency matrix of the interval [0, 0,8). The proposed model outperforms conventional machine learning and deep learning algorithms such as linear regression (LR), K-nearest neighbors (KNN), Support vector regression (SVR), Decision tree, lasso, and artificial neural network (ANN). The absolute error between the actual and predicted deformation is used to evaluate the proposed model, which is less than 2 millimeters for most test set points.

Alexander R. Pietros, Kacper Rebeszko, Jacob R. Rosenbaum et al.

Optically active defects in silica have been studied for decades and are often indicators of network irregularities such as those that might result from optical or mechanical damage. They are well-known to be weak emitters and are usually present in relatively low concentration, thus precluding their use in a wide range of applications, including sensing and laser gain. Here, a new paradigm in intense defect emission in the visible wavelength range from a nominally passive optical fiber is presented. Optical fiber starting with 100 mol % BaF2 precursor core material and a pure silica cladding was successfully drawn utilizing the molten core method. These fibers demonstrate an intense, yet unexpected, green photoluminescence peaking near 537 nm (in addition to a second, weaker band near 704 nm) arising from relatively low-power CW pumping in the near-infrared at 976 nm. To understand the origins of this emission, absorption across the optical spectrum is analyzed and photoluminescence via excitation in both the visible and near-infrared wavelength ranges is studied. In addition, Raman spectra, decay lifetimes, magnetization curves, and temperature dependence measurements were collected. The emission spectra maintained a Pekarian-like spectral shape, suggesting an optically active defect as the mechanism behind the green emission. The results presented herein point towards the most likely origin being silanone or dioxasilyrane groups usually associated with surface defects. Importantly, such fibers, fabricated through less conventional methods and possessing novel compositions, may prove to be key in further extending the range of possibilities in defect engineering to well beyond what was previously thought possible.

Fei Ding, Shiwei Tang, S. Bozhevolnyi

Similar to frequency, phase, and amplitude, polarization is an intrinsic property of light. Generally, polarization describes the oscillation direction of the electric field and indicates the transverse nature of light. As polarization is uncorrelated with frequency, phase, and amplitude, it could extend the information channels and has be widely used in practical applications. However, the majority of light sources, such as the sun, emit unpolarized light with randomly oriented oscillation directions. With polarization optics, such as polarizers and wave plates, unpolarized light with randomly oriented vibrations is transformed into either a linear, circular, or elliptical light wave. However, conventional optical components that allow to manipulate the state of polarization (SOP) are usually based on the accumulated phase retardation between two orthogonally polarized electric fields when light propagates a distance much larger than its wavelength. As a consequence, traditional polarization optics are bulky, thereby limiting the potential of miniaturization and dense integration in advanced photonic devices and systems. Therefore, it is highly desired to fully manipulate the SOP with a truly compact device that possesses excellent performance and multiple functionalities. In recent years, optical metasurfaces, the 2D inhomogeneous interface composed of planar meta-atoms, have shown their unprecedented capabilities of controlling the optical fields with a subwavelength spatial resolution at the single meta-atom level. Specifically, the phase, amplitude, and even frequency of light can be tailored at will through judiciously designed metaatoms with particular responses. As a result, optical metasurfaces have gained much attention and started to replace conventional bulky optics with planar, compact, and high-performance metadevices, especially for polarization optics. In particular, polarization-encoded metasurfaces exhibit the advantages of flexibility, versatility, ease of fabrication and integration. Herein, we review the basic principles and emerging applications of polarization-encoded functional metasurfaces in the optical regime. We mainly focus our attention on the optical metasurfaces although there are many fantastic metasurface-enabled polarization converters and polarization-multiplexing devices in the microwave and terahertz regimes. After the description of polarization (Section 2), we introduce how to convert and detect the SOP of light with metasurfaces (Section 3 and 4). Then we summarize the main achievements in polarization-multiplexed metadevices (Section 5). Finally, we end up this review with a short conclusion and personal outlook on potential directions in this fast-growing research area (Section 6).

M. Martinod, B. Norris, P. Tuthill et al.

Characterisation of exoplanets is key to understanding their formation, composition and potential for life. Nulling interferometry, combined with extreme adaptive optics, is among the most promising techniques to advance this goal. We present an integrated-optic nuller whose design is directly scalable to future science-ready interferometric nullers: the Guided-Light Interferometric Nulling Technology, deployed at the Subaru Telescope. It combines four beams and delivers spatial and spectral information. We demonstrate the capability of the instrument, achieving a null depth better than 10−3 with a precision of 10−4 for all baselines, in laboratory conditions with simulated seeing applied. On sky, the instrument delivered angular diameter measurements of stars that were 2.5 times smaller than the diffraction limit of the telescope. These successes pave the way for future design enhancements: scaling to more baselines, improved photonic component and handling low-order atmospheric aberration within the instrument, all of which will contribute to enhance sensitivity and precision. Nulling interferometry is a technique combining lights from different telescopes or apertures to observe weak sources nearby bright ones. The authors report the first nulling interferometer implemented in a photonic chip doing spectrally dispersed nulling on several baselines, simultaneously.

R. Lovelace, R. Félix, D. Carlino

Origin-Destination (OD) datasets provide vital information on how people travel between areas in many cities, regions and countries worldwide. OD datasets are usually represented geographically with straight lines or routes between zone centroids. For active travel, this geographic representation has substantial limitations, especially when zone origins and centroids are large: only using a single centroid origin/destination for each large zone results in sparse route networks covering only a small fraction of likely walking and cycling routes. This paper implements and explores the use of jittering and different routing options to overcome this limitation, thereby adding value to aggregate OD data to support investment in sustainable transport infrastructure. The route network results — generated from on an open dataset representing cycling trips in Lisbon, Portugal — were compared with a ground-truth dataset from 67 count locations distributed throughout the city. This approach enabled exploration of which jittering parameters and routing options lead to the most accurate route network results approximating the real geographic distribution of cycling trips in the study area. We found that jittering and disaggregating OD data, combined with routing using low level of traffic stress (quieter) preferences resulted in the most accurate route networks. We conclude that a combined approach involving 1) jittering with intermediate levels of disaggregation and 2) careful selection of routing options can lead to much more realistic route networks than using established OD processing techniques. The methods can be deployed to support evidence-based investment in strategic cycling and other sustainable transport networks in cities worldwide.

Kebin Shi

Abstract Birefringence-involved phase matching is demonstrated to be a novel mechanism to generate transform limited solitary pulses in an ultrafast mode-locking fiber laser cavity with normal dispersion.

M. P. Hokmabadi, Nicholas S. Nye, R. El-Ganainy et al.

Stability through symmetry A common route to get more light out of a laser system is to couple multiple lasers to form an array. However, instabilities owing to cross-talk and interference between different modes of individual cavities is generally detrimental to performance and could ultimately be damaging to the laser cavities. Hokmabadi et al. applied notions derived from supersymmetry, a theory developed in high-energy physics to describe the make-up and properties of particles, to design a stable array of semiconductor lasers (see the Perspective by Kottos). Based on symmetry arguments, the method is scalable and could provide a practical platform to design and develop complex photonic systems. Science, this issue p. 623; see also p. 586 Principles taken from supersymmetry theory are used to design a stable semiconductor laser array. Scaling up the radiance of coupled laser arrays has been a long-standing challenge in photonics. In this study, we demonstrate that notions from supersymmetry—a theoretical framework developed in high-energy physics—can be strategically used in optics to address this problem. In this regard, a supersymmetric laser array is realized that is capable of emitting exclusively in its fundamental transverse mode in a stable manner. Our results not only pave the way toward devising new schemes for scaling up radiance in integrated lasers, but also, on a more fundamental level, could shed light on the intriguing synergy between non-Hermiticity and supersymmetry.

S. Colburn, Yiren Chu, Eli Shlizerman et al.

The parallelism of optics and the miniaturization of optical components using nanophotonic structures, such as metasurfaces, present a compelling alternative to electronic implementations of convolutional neural networks. The lack of a low-power optical nonlinearity, however, requires slow and energy-inefficient conversions between the electronic and optical domains. Here, we design an architecture that utilizes a single electrical to optical conversion by designing a free-space optical frontend unit that implements the linear operations of the first layer with the subsequent layers realized electronically. Speed and power analysis of the architecture indicates that the hybrid photonic-electronic architecture outperforms a fully electronic architecture for large image sizes and kernels. Benchmarking of the photonic-electronic architecture on a modified version of AlexNet achieves high classification accuracies on images from the Kaggle's Cats and Dogs challenge and MNIST databases.

V. Bharadwaj, O. Jedrkiewicz, J. Hadden et al.

Diamond has attracted great interest in the quantum optics community thanks to its nitrogen vacancy (NV) center, a naturally occurring impurity that is responsible for the pink coloration of some diamond crystals. The NV spin state with the brighter luminescence yield can be exploited for spin readout, exhibiting millisecond spin coherence times at ambient temperature. In addition, the energy levels of the ground state triplet of the NV are sensitive to external fields. These properties make NVs attractive as a scalable platform for efficient nanoscale resolution sensing based on electron spins and for quantum information systems. Integrated diamond photonics would be beneficial for optical magnetometry, due to the enhanced light–matter interaction and associated collection efficiency provided by waveguides, and for quantum information, by means of the optical linking of NV centers for long-range entanglement. Diamond is also compelling for microfluidic applications due to its outstanding biocompatibility, with sensing functionality provided by NV centers. Furthermore, laser written micrographitic modifications could lead to efficient and compact detectors of high energy radiation in diamond. However, it remains a challenge to fabricate optical waveguides, graphitic lines, NVs and microfluidics in diamond. In this Review, we describe a disruptive laser nanofabrication method based on femtosecond laser writing to realize a 3D micro-nano device toolkit for diamond. Femtosecond laser writing is advantageous compared to other state of the art fabrication technologies due to its versatility in forming diverse micro and nanocomponents in diamond. We describe how high quality buried optical waveguides, low roughness microfluidic channels, and on-demand NVs with excellent spectral properties can be laser formed in single-crystal diamond. We show the first integrated quantum photonic circuit in diamond consisting of an optically addressed NV for quantum information studies. The rapid progress of the field is encouraging but there are several challenges which must be met to realize future quantum technologies in diamond. We elucidate how these hurdles can be overcome using femtosecond laser fabrication, to realize both quantum computing and nanoscale magnetic field sensing devices in synthetic diamond.

Philipp‐Immanuel Schneider, Xavier Garcia Santiago, V. Soltwisch et al.

Numerical optimization is an important tool in the field of computational physics in general and in nano-optics in specific. It has attracted attention with the increase in complexity of structures that can be realized with nowadays nano-fabrication technologies for which a rational design is no longer feasible. Also, numerical resources are available to enable the computational photonic material design and to identify structures that meet predefined optical properties for specific applications. However, the optimization objective function is in general non-convex and its computation remains resource demanding such that the right choice for the optimization method is crucial to obtain excellent results. Here, we benchmark five global optimization methods for three typical nano-optical optimization problems: \removed{downhill simplex optimization, the limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm, particle swarm optimization, differential evolution, and Bayesian optimization} \added{particle swarm optimization, differential evolution, and Bayesian optimization as well as multi-start versions of downhill simplex optimization and the limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm}. In the shown examples from the field of shape optimization and parameter reconstruction, Bayesian optimization, mainly known from machine learning applications, obtains significantly better results in a fraction of the run times of the other optimization methods.

Romain Zinsou, Pu Li, Zhensen Gao et al.

We propose and numerically demonstrate the generation of wideband millimeter-wave (mmW) flat chaos with controllable power spectrum by injection of chaotic signal from external cavity semiconductor laser (ECSL) into optical time lens with noise phase modulation. Simulation results indicate consistent elimination of the ECSL relaxation oscillation frequency domination over the RF spectrum for large scale parameters of the optical time lens module and a wideband flat chaos, whose efficient bandwidth rapidly increases with the bandwidth of the noise signal driving the phase modulator and phase modulation index. Besides, we show that the time delay signature suppression can be concurrently achieved for moderate values of the noise bandwidth and phase modulation index. The proposed wideband mmW flat chaos exhibits great potential applications for ultrahigh-speed chaos communications, mmW radars and macroscopic mmW noise source required for mmW research and design.

O. Takayama, J. Sukham, R. Malureanu et al.

The photonic spin Hall effect [1] or spin Hall effect of light [2] is the photonic analog of the spin Hall effect occurring with charge carriers in solid-state systems. Typically, this phenomenon takes place when a light beam refracts at an air-glass interface, or when it is projected onto an oblique plane, the latter effect being known as the geometric spin Hall effect of light [3]. In general, the photonic spin Hall effect leads to a polarization dependent transverse shift of a light peak intensity [3,4]. An example of the latter effect is the transverse Imbert-Federov beam shift [3], which happens for paraxial beams reflected or refracted at a sharp inhomogeneity of an isotropic optical interface. Potential applications of the photonic spin Hall effect in spin-dependent beam splitters, optical diodes [1], and surface sensors are considered in various fields in photonics, such as nanophotonics, plasmonics, metamaterials, topological optics, and quantum optics [1,2].

L. Cappelletti, R. Ruscica, M. M. Salvia et al.

Surface soil moisture (SSM) dry-downs have been employed to compare independent data sources on the dynamics of water in soils, including such remote sensing, land surface models and in-situ measurements, which are often difficult to contrast with standard methodologies. The soil drying approach summarizes the soil response to climate as well as surface conditions during a dry period. In this work it is estimated as the SSM e-folding decay, named as dry-down time scale. This is the first assessment over eastern Cordoba, Argentina, a region with a very high cultivated land fraction that was subject of important agricultural changes in the last decades. SMOS SSM product (derived from microwave measurements at L band) is validated with in-situ SSM measurements provided by the National Commission for Space Activities during 2012–2018. Both products agree in showing that the austral spring season has the largest number of dry-down events for the whole period. The dry-down time scale sensitivity to the chosen detection method as well as the data sampling frequency is larger in summer than in spring. A faster soil drying in SMOS than in In-situ SSM is found, likely as a consequence of the shallower sensing depth of the first. This dependency seems to be more important than the temporal sampling frequency in the SSM data.

Wagdy A. Alathwary, Essam Saleh Altubaishi

In this paper, we introduce a decode-and-forward multi-hop hybrid free-space optical/radio frequency (FSO/RF) system. The FSO link is assumed to follow Gamma-Gamma distribution with the combined effects of pointing errors and path loss under intensity modulation with direct detection technique, and the RF link is assumed to follow Nakagami-m distribution. In particular, we derive closed-form expressions for the outage probability and ergodic capacity and analyze the system performance under the effect of different weather conditions in addition to the effect of pointing errors. The results show that the multi-hop hybrid system improves the performance even under adverse weather conditions and strong pointing errors. Furthermore, Monto Carlo simulations are provided for validation.