Hasil untuk "Applied optics. Photonics"

M. Miri, A. Alú

Exceptional points in optics Many complex systems operate with loss. Mathematically, these systems can be described as non-Hermitian. A property of such a system is that there can exist certain conditions—exceptional points—where gain and loss can be perfectly balanced and exotic behavior is predicted to occur. Optical systems generally possess gain and loss and so are ideal systems for exploring exceptional point physics. Miri and Alù review the topic of exceptional points in photonics and explore some of the possible exotic behavior that might be expected from engineering such systems. Science, this issue p. eaar7709 BACKGROUND Singularities are critical points for which the behavior of a mathematical model governing a physical system is of a fundamentally different nature compared to the neighboring points. Exceptional points are spectral singularities in the parameter space of a system in which two or more eigenvalues, and their corresponding eigenvectors, simultaneously coalesce. Such degeneracies are peculiar features of nonconservative systems that exchange energy with their surrounding environment. In the past two decades, there has been a growing interest in investigating such nonconservative systems, particularly in connection with the quantum mechanics notions of parity-time symmetry, after the realization that some non-Hermitian Hamiltonians exhibit entirely real spectra. Lately, non-Hermitian systems have raised considerable attention in photonics, given that optical gain and loss can be integrated as nonconservative ingredients to create artificial materials and structures with altogether new optical properties. ADVANCES As we introduce gain and loss in a nanophotonic system, the emergence of exceptional point singularities dramatically alters the overall response, leading to a range of exotic functionalities associated with abrupt phase transitions in the eigenvalue spectrum. Even though such a peculiar effect has been known theoretically for several years, its controllable realization has not been made possible until recently and with advances in exploiting gain and loss in guided-wave photonic systems. As shown in a range of recent theoretical and experimental works, this property creates opportunities for ultrasensitive measurements and for manipulating the modal content of multimode lasers. In addition, adiabatic parametric evolution around exceptional points provides interesting schemes for topological energy transfer and designing mode and polarization converters in photonics. Lately, non-Hermitian degeneracies have also been exploited for the design of laser systems, new nonlinear optics phenomena, and exotic scattering features in open systems. OUTLOOK Thus far, non-Hermitian systems have been largely disregarded owing to the dominance of the Hermitian theories in most areas of physics. Recent advances in the theory of non-Hermitian systems in connection with exceptional point singularities has revolutionized our understanding of such complex systems. In the context of optics and photonics, in particular, this topic is highly important because of the ubiquity of nonconservative elements of gain and loss. In this regard, the theoretical developments in the field of non-Hermitian physics have allowed us to revisit some of the well-established platforms with a new angle of utilizing gain and loss as new degrees of freedom, in stark contrast with the traditional approach of avoiding these elements. On the experimental front, progress in fabrication technologies has allowed for harnessing gain and loss in chip-scale photonic systems. These theoretical and experimental developments have put forward new schemes for controlling the functionality of micro- and nanophotonic devices. This is mainly based on the anomalous parameter dependence in the response of non-Hermitian systems when operating around exceptional point singularities. Such effects can have important ramifications in controlling light in new nanophotonic device designs, which are fundamentally based on engineering the interplay of coupling and dissipation and amplification mechanisms in multimode systems. Potential applications of such designs reside in coupled-cavity laser sources with better coherence properties, coupled nonlinear resonators with engineered dispersion, compact polarization and spatial mode converters, and highly efficient reconfigurable diffraction surfaces. In addition, the notion of the exceptional point provides opportunities to take advantage of the inevitable dissipation in environments such as plasmonic and semiconductor materials, which play a key role in optoelectronics. Finally, emerging platforms such as optomechanical cavities provide opportunities to investigate exceptional points and their associated phenomena in multiphysics systems. Ubiquity of non-Hermitian systems, supporting exceptional points, in photonics. (A) A generic non-Hermitian optical system involving two coupled modes with different detuning, ±ω1,2, and gain-loss values, ±γ1,2, coupled at rate of μ. The real part of the associated eigenvalues in a two-dimensional parameter space of the system, revealing the emergence of an exceptional point (EP) singularity. a1 and a2 are the modal amplitudes. (B to E) A range of different photonic systems, which are all governed by the coupled-mode equations. (B) Two coupled lasers pumped at different rates. (C) Dynamical interaction between optical and mechanical degrees of freedom in an optomechanical cavity. (D) A resonator with counter-rotating whispering gallery modes. CW, clockwise; CCW, counterclockwise. (E) A thin metasurface composed of coupled nanoantennas as building blocks. CREDITS: IMAGE IN (A) BASED ON A CONCEPT FROM H. HODAEI ET AL., SCIENCE 346, 975 (2014); IMAGE IN (D) BASED ON CONCEPTS FROM W. CHEN ET AL., NATURE 548, 192 (2017). Exceptional points are branch point singularities in the parameter space of a system at which two or more eigenvalues, and their corresponding eigenvectors, coalesce and become degenerate. Such peculiar degeneracies are distinct features of non-Hermitian systems, which do not obey conservation laws because they exchange energy with the surrounding environment. Non-Hermiticity has been of great interest in recent years, particularly in connection with the quantum mechanical notion of parity-time symmetry, after the realization that Hamiltonians satisfying this special symmetry can exhibit entirely real spectra. These concepts have become of particular interest in photonics because optical gain and loss can be integrated and controlled with high resolution in nanoscale structures, realizing an ideal playground for non-Hermitian physics, parity-time symmetry, and exceptional points. As we control dissipation and amplification in a nanophotonic system, the emergence of exceptional point singularities dramatically alters their overall response, leading to a range of exotic optical functionalities associated with abrupt phase transitions in the eigenvalue spectrum. These concepts enable ultrasensitive measurements, superior manipulation of the modal content of multimode lasers, and adiabatic control of topological energy transfer for mode and polarization conversion. Non-Hermitian degeneracies have also been exploited in exotic laser systems, new nonlinear optics schemes, and exotic scattering features in open systems. Here we review the opportunities offered by exceptional point physics in photonics, discuss recent developments in theoretical and experimental research based on photonic exceptional points, and examine future opportunities in this area from basic science to applied technology.

Gordon Wetzstein, A. Ozcan, S. Gigan et al.

M. Parto, Yuzhou G. N. Liu, B. Bahari et al.

Abstract In the past few years, concepts from non-Hermitian (NH) physics, originally developed within the context of quantum field theories, have been successfully deployed over a wide range of physical settings where wave dynamics are known to play a key role. In optics, a special class of NH Hamiltonians – which respects parity-time symmetry – has been intensely pursued along several fronts. What makes this family of systems so intriguing is the prospect of phase transitions and NH singularities that can in turn lead to a plethora of counterintuitive phenomena. Quite recently, these ideas have permeated several other fields of science and technology in a quest to achieve new behaviors and functionalities in nonconservative environments that would have otherwise been impossible in standard Hermitian arrangements. Here, we provide an overview of recent advancements in these emerging fields, with emphasis on photonic NH platforms, exceptional point dynamics, and the very promising interplay between non-Hermiticity and topological physics.

Shuihua Yang, Mengqi Liu, Changying Zhao et al.

Shaowei Liu, Dezhong Zhang, Lei Wang et al.

Abstract The integration of crystallographic control into solution-processed perovskite films remains a challenge for efficient light emission, as disordered optical dipoles fundamentally limit photon extraction, a bottleneck constraining both classical and quantum planar optoelectronic devices. Here, we address this by developing an in situ formation strategy for oriented quasi-2D perovskite nanosheets within films via ligand-engineered crystallization. By designing and orchestrating steric hindrance and π–π interactions of ligands, we direct the crystallization kinetics to yield regular face-on nanosheets exhibiting enhanced horizontal transition dipole moment orientation compared to conventional isotropic films. The in situ architectural control also elevates both the photoluminescence quantum yield beyond 90% and carrier mobility comparable to 3D perovskite levels. These synergies enable perovskite light-emitting diodes (PeLEDs) with an external quantum efficiency (EQE) of 31.2% for pure-red emission at 635 nm, comparing favorably to other pure-red PeLEDs. Concurrently, the peak luminance and operational stability of the in situ nanosheet PeLEDs exhibit significant improvements.

Changqing Wang, Zhou Fu, Wenbo Mao et al.

Sajid Ali, Shafiq Ahmad, A. Ullah et al.

Shuyi Li, Wei Luo, Zhenyu Li et al.

Optical modulators are essential building blocks for high-capacity optical communication and massively parallel computing. Among all types of optical modulators, travelling-wave Mach-Zehnder modulators (TW-MZMs) featuring high speed and efficiency are widely used, and have been developed on a variety of integrated material platforms. Existing methods to design and simulate TW-MZMs so far strongly rely on the peculiar material properties, and thus inevitably involve complicated electrical-circuit models. As a result, these methods diverge significantly. In addition, they become increasingly inefficient and inaccurate for TW-MZMs with extending length and levitating modulation speed, posing formidable challenges for millimeter-wave and terahertz operation. Here, we present an innovative perspective to understand and analyze high-speed TW-MZMs. Our perspective leverages nonlinear optics and complex band structures of RF photonic crystals, and is thus entirely electromagnetic-wave-based. Under this perspective, we showcase the design, optoelectronic simulation and experimental validation of high-speed TW-MZMs based on Si and LiNbO$_3$, and further demonstrate unambiguous advantages in simplicity, accuracy and efficiency over conventional methods. Our approach can essentially be applied to nearly any integrated material platform, including those based on semiconductors and electro-absorption materials. With high-frequency electrode designs and optoelectronic co-simulation, our approach facilitates the synergy and convergence of electronics and photonics, and offers a viable route to constructing future high-speed millimeter-wave and terahertz photonics and quantum systems.

L. Leonforte, X. Sun, D. Valenti et al.

We present a general framework to tackle quantum optics problems with giant atoms, i.e. quantum emitters each coupled non-locally to a structured photonic bath (typically a lattice) of any dimension. The theory encompasses the calculation and general properties of Green’s functions, atom-photon bound states, collective master equations and decoherence-free Hamiltonians (DFHs), and is underpinned by a formalism where a giant atom is formally viewed as a normal atom lying at a fictitious location. As a major application, we provide for the first time a general criterion to predict/engineer DFHs of giant atoms, which can be applied both in and out of the photonic continuum and regardless of the structure or dimensionality of the photonic bath. This is used to show novel DFHs in 2D baths such as a square lattice, photonic graphene and an extended photonic Lieb lattice.

Marina Romanova, Sergii Chertopalov, Yuri Dekhtyar et al.

The charge trapping phenomenon in the SiO2 layer of Si/SiO2 substrates during the electron beam deposition of CaF2 thin films of varying thicknesses (50–277 nm) was studied. Photoelectron emission (PE) spectroscopy was employed to analyze electron trapping mechanisms induced by the deposition process. Distinct peaks corresponding to electron traps in the SiO2 layer were identified in the PE spectra of CaF2 films. The intensity of these peaks varied with the film thickness and the accumulated electron irradiation dose. The study also investigated the relaxation of the PE spectra in both vacuum and air environments. In a vacuum, the PE peaks and integrated PE intensity remained stable for at least 24 h for CaF2 films of all thicknesses. When exposed to air, the PE peaks persisted for several days in films 125 nm thick or thinner but relaxed within several hours in 277 nm films. This rapid relaxation was attributed to a relatively high irradiation dose (about 2.5 mC) obtained during the fabrication of the 277 nm film, leading to an increased concentration of ionized F centers at the SiO2–CaF2 interface and the formation of (O2–-VA) centers upon air exposure. The relaxation of the PE spectrum intensity was attributed to electron transfer from SiO2 traps to (O2–-VA) centers. Furthermore, the possibility of a 260 nm electron escape depth for CaF2 material was confirmed.

Chang-Xiao Li

We propose a theoretical scheme to enhance quantum coherence and obtain steady-state coherence by combining quantum feedback control and noise-assisted preparation. We investigate the effects of quantum-jump-based feedback control and noise field on the quantum coherence and excited-state population between two atoms inside an optical cavity where a noise field drives one, and the other is under quantum feedback control. It is found that steady quantum coherence can be achieved by adding an external noise field, and the quantum feedback can prolong the coherence time with partial suppression of the spontaneous emission of atoms. In addition, we study the influence of the joint action of quantum feedback and noise-assisted preparation on quantum coherence and show that the combined action of feedback control and noise-assisted preparation is more effective in enhancing steady coherence. The findings of our research offer some general guidelines for improving the steady-state coherence of coupled qubit systems and have the potential to be applied in the realm of quantum information technology.

Hongfei Wang, Xiujuan Zhang, Jin-Guo Hua et al.

The notion of non-Hermitian optics and photonics rooted in quantum mechanics and photonic systems has recently attracted considerable attention ushering in tremendous progress on theoretical foundations and photonic applications, benefiting from the flexibility of photonic platforms. In this review, we first introduce the non-Hermitian topological physics from the symmetry of matrices and complex energy spectra to the characteristics of Jordan normal forms, exceptional points, biorthogonal eigenvectors, Bloch/non-Bloch band theories, topological invariants and topological classifications. We further review diverse non-Hermitian system branches ranging from classical optics, quantum photonics to disordered systems, nonlinear dynamics and optomechanics according to various physical equivalences and experimental implementations. In particular, we include cold atoms in optical lattices in quantum photonics due to their operability at quantum regimes. Finally, we summarize recent progress and limitations in this emerging field, giving an outlook on possible future research directions in theoretical frameworks and engineering aspects.

F. Schindler, S. Pari, S. Meissl et al.

Open Science is a catalyst for innovation. Across the Earth Observation value chain, from R&D to prototyping new products and development of commercial applications, openness can play an important role by promoting long-term sustainable, community-contributed science and technology. The FAIR principles provide essential support to implementing Open Science, by offering guidelines for how researchers can adapt their EO and Earth Science practice to enable that their work (taking place increasingly in the cloud) and results are discovered, accessed, used, and reproduced by others. The Open Science Data Catalogue (OSC) (https://opensciencedata.esa.int) is an ESA Open Science activity aiming to enhance the discoverability and use of the various scientific and value-added results (i.e. data, code, documentation) achieved in Earth System Science research activities funded by ESA EO. The OSC provides open access for the scientific community to geoscience products (based on EO data from ESA and non-ESA missions and other geospatial information and models) across the whole spectrum of Earth Science domains. The OSC adheres to FAIR principles and promotes reproducibility of scientific studies. The OSC makes use of various Open-Source geospatial technologies such as pycsw, PySTAC, and OpenLayers and tries to contribute back to these projects in terms of software and standardisation. This paper reviews the EO OSC architecture, technology stack, and illustrates how this tool can be used to discover and publish Earth System Science products from ESA activities. It also looks at future evolutions of the product and how it contributes to ESA’s EO Open Science and Innovation goals.

Zhifei Hu, Xiangchao Zhang, Wei Lang et al.

With the fast development in the fields of photovoltaics and integrated circuits, the measurement of surface topographies and micro-scaled defects has attracted intensive interests. However, existing measurement methods are time-consuming and unsuitable for in-situ detection. Therefore, a fast topographic measurement method is developed based on the deflectometric microscope system. Microscopic deflectometry is an attractive tool due to its high sensibility to surface slopes and large dynamic range of measurement. For the quantitative reconstruction of surface topographies from slopes, an integration method is developed based on the minimum spanning tree, and the integration path is designed based on a sparse representation and a curl map. The robustness and accuracy of the integration method are validated by numerical simulation and experiments. This method can achieve a high measurement accuracy with a high lateral resolution and a depth of field of 90 μm, hereby improving the manufacturing efficiency and quality of opto-electronics functional devices.

Serguei Smirnov, Aleksandra Przewłoka, Aleksandra Krajewska et al.

Materials with tunable dielectric properties are highly relevant for terahertz (THz) applications. Herein, the tuning of the dielectric response of single‐walled carbon nanotube layers by light illumination is studied for applications to THz phase shifters. The dependence of the length of individual nanotubes on the THz photoconductivity of the network is experimentally investigated in the frequency range of 0.2–1 THz by time‐domain spectroscopy (TDS). The effective conductivity of the networks is described by a theoretical model that fits the measured dielectric function. Terahertz phase shifters are realized with the carbon nanotube layers as the optically tunable element deposited on the wall of rectangular dielectric waveguides. The phase of the electromagnetic wave propagating in the waveguide is shown to be tunable by illuminating the nanotubes. A linear phase shift with the frequency is measured between 75 and 500 GHz with a low change in amplitude due to the illumination.

K. A. Adiputri

To allow a more comprehensive, adaptable, and accessible Historic Structure Report (HSR), an approach to transform HSR to Digital HSR (DHSR) utilizing Building Information Modelling (BIM) will be evaluated in this paper. HSR is the type of historic documentation ruled by the National Park Service (NPS), a U.S. Department of the Interior bureau. It is directed to owners of historic buildings to help with decisions on the structure and provide an information resource for future uses. BIM’s ability to enhance the current HSR process by closing the disconnection between visual and information could suggest its potential utility in complementing or even substituting physical HSR. This research will be conducted in two approaches to support the proposal for a standard application of DHSR. The first approach is by analyzing the current guideline of HSR, which will include the evaluation of the NPS’s “Preservation Brief.” The second approach is to evaluate the BIM features, potential, and challenges for Digital HSR by analyzing the software as a user. The result of this study would be a proposed protocol of the DHSR, as an application guideline.

B. Kress

When compared to other enabling technology fields such as Electronic Engineering or Computer Science, Optics and Photonics stands out to be by far the oldest field of research, and yet the one still standing today at the forefront of research, consumer electronics, transformation industry, communication, health, biotech and many more. From solving the mysteries of our universe to the development of the latest smart phones and the fastest internet lines, the field of Optics and Photonics has proven over and over to be at the cornerstone for everything we take for granted today. This field has been associated with many successive market booms, and sometimes also bubbles, but the underlying technology build by its exceptional engineers never gets wasted or lost, providing valuable key building blocks to fuel the “next big thing” Full Text: PDF References https://money.cnn.com/2001/12/18/technology/q_yearend_telecom DirecLink https://money.cnn.com/2010/11/09/technology/jdsu_qualcomm/index.htm DirectLink https://www.forbes.com/global/1999/1129/098_01.html?sh=290252831d0c DirectLink B. Kress, Applied Digital Optics: From Micro-optics to Nanophotonics (John Wiley 2007). DirectLink K. Curtis, D. Psaltis, "Cross talk in phase-coded holographic memories", J Opt Soc Am. 10(12), 2547 (1993). CrossRef W.S. Colburn, B.J. Chang, "Holographic combiners for head up displays", Tech Report No. AFAL-TR-77-110, (1977). DirectLink J. Kimmel, T. Levola, P. Saarikko, "A novel diffractive backlight concept for mobile displays", J Soc Inf Disp 16(2), (2008). CrossRef

K. Cho, K. Naoki

The latest IPCC report clearly stated that the human influence is the main reason of sea ice reduction in the Arctic. Importance of sea ice monitoring from space is increasing. In addition, the heat flux of ice in thin ice areas is strongly affected by the ice thickness difference. Therefore, ice thickness is one of the important parameters of sea ice. The authors have been studying on extracting thin ice areas using optical sensor such as MODIS for years. In this paper, the authors summarized the procedure of our study starting from comparing in-situ measurement of ice thickness with high resolution optical sensor RSI data, and finally developing the thin ice area extraction algorithm using MODIS. Estimating ice thickness from optical sensor data is not easy. However, through our study, the authors have verified the possibility of extracting thin ice areas using optical sensor data observed from satellites. In this study, the authors define “thin ice areas” as ice which thickness is less than about 30 cm with reflectance much lower than thick ice. The basic idea of the algorithm is to use the scatterplots of MODIS band 1 & 2 reflectance and extract thin ice areas using the distribution difference of thin ice against water, thick ice, clouds. Not all but most of the thin ice areas could be extracted using the algorithm.

Fa-tang CHEN, Feng WU

Although millimeter-wave communication technology can meet the design indicators of 5th Generation Mobile Networks (5G) communication, the path loss of millimeter-wave in the transmission process seriously affects its transmission performance. Therefore, waveform shaping technology is needed to concentrate the transmission energy to reduce the impact of path loss. However, the traditional Discontinuous Reception (DRX) mechanism will lead to beam misalignment in the beam shaping system, which is no longer applicable in 5G system. In order to solve the above problems, this research proposes a long-period Adjustable Orientation DRX (A-ODRX) mechanism. The beam search state is merged into the long period state to overcome beam misalignment, and a long period incremental coefficient is introduced to save power consumption. The semi-Markov chain and the European Telecommunications Standards Institute (ETSI) traffic model are used to simulate the A-ODRX mechanism. The average delay, energy saving effect and beam misalignment probability of A-ODRX mechanism are analyzed in simulation. The results show that the A-ODRX mechanism can significantly reduce the beam misalignment probability while effectively reducing the energy consumption of the terminal.

Jun Zheng Zhang, Ke Ke

Abstract For visible light communication (VLC), the light signals are transmitted without optical fibers or any sort of wave-guiding. Due to the inherent broadcast nature, physical-layer security emerges as a promising method to protect information delivery from eavesdropping. As for the secrecy capacity of VLC channel, there exist two features. In one way, the limited optical power makes the common capacity expressions in radio-frequency (RF) communication unapplicable for VLC. In another way, several correlated geometrical parameters directly alters the Lambertian model of indoor VLC channel, which gives the secrecy capacity more meanings. However, the issue considering both aspects has not been studied recently. In this paper, from the practical scenarios, we extract a typical geometrical model to reveal the mobility principles of the legitimate receiver and the eavesdroppers. Then, we character two typical distributions of the geometrical parameter. Correspondingly, we derive the upper and lower bounds on the average secrecy capacity, which have the closed forms. Finally, simulation results show that our upper and lower bounds are tight at high optical signal-to-noise rates (OSNRs). Moreover, the geometrical features of VLC systems and distribution parameters of the receiver mobility are effectively reveal by the bounds.