Hasil untuk "Optics. Light"

Ashleyj . Welch, M. Gemert

Xudong Zhang, Yilin Liu, Jiecai Han et al.

Ultracompact sources of circularly polarized light are important for classical and quantum optical information processing. Conventional approaches for generating chiral emission are restricted to excitation power ranges and fail to provide high-quality radiation with perfect polarization conversion. We used the physics of chiral quasi-bound states in the continuum to demonstrate the efficient and controllable emission of circularly polarized light from resonant metasurfaces. Exploiting intrinsic chirality and giant field enhancement, we revealed how to simultaneously modify and control spectra, radiation patterns, and spin angular momentum of photoluminescence and lasing without any spin injection. The superior characteristics of chiral emission and lasing promise multiple applications in nanophotonics and quantum optics. Description Another twist for metasurfaces Metasurfaces are specially designed arrays of dielectric components that transform the function of bulk optical components into thin films. Exploiting the physics of bulk states in the continuum for the highly efficient trapping of light, Zhang et al. demonstrate metasurfaces that operate as a source of chiral light (see the Perspective by Forbes). Using a dielectric metasurface doped with light-emitting molecules, they were able to produce chiral photoluminescence and lasing. This approach will be useful for the development of integrated optical devices. —ISO Cobalt carbonyl catalysts prove stable at lower gas pressure than previously thought.

F. Monticone, N. Estakhri, A. Alú

Yang Chen, Huachun Deng, Xinbo Sha et al.

Photons with spin angular momentum possess intrinsic chirality, which underpins many phenomena including nonlinear optics^ 1 , quantum optics^ 2 , topological photonics^ 3 and chiroptics^ 4 . Intrinsic chirality is weak in natural materials, and recent theoretical proposals^ 5 – 7 aimed to enlarge circular dichroism by resonant metasurfaces supporting bound states in the continuum that enhance substantially chiral light–matter interactions. Those insightful works resort to three-dimensional sophisticated geometries, which are too challenging to be realized for optical frequencies^ 8 . Therefore, most of the experimental attempts^ 9 – 11 showing strong circular dichroism rely on false/extrinsic chirality by using either oblique incidence^ 9 , 10 or structural anisotropy^ 11 . Here we report on the experimental realization of true/intrinsic chiral response with resonant metasurfaces in which the engineered slant geometry breaks both in-plane and out-of-plane symmetries. Our result marks, to our knowledge, the first observation of intrinsic chiral bound states in the continuum with near-unity circular dichroism of 0.93 and a high quality factor exceeding 2,663 for visible frequencies. Our chiral metasurfaces may lead to a plethora of applications in chiral light sources and detectors, chiral sensing, valleytronics and asymmetric photocatalysis. Chiral metasurfaces have been produced, with experimental observation of intrinsic chiral bound states in the continuum, which may lead to applications in chiral light sources and detectors, chiral sensing, valleytronics and asymmetric photocatalysis.

Jie Bao, M. Bawendi

Zhuojun Liu, Yi Xu, Ye Lin et al.

Sharp electromagnetic resonances play an essential role in physics in general and optics in particular. The last decades have witnessed the successful developments of high-quality (Q) resonances in microcavities operating below the light line, which however is fundamentally challenging to access from free space. Alternatively, metasurface-based bound states in the continuum (BICs) offer a complementary solution of creating high-Q resonances in devices operating above the light line, yet the experimentally demonstrated Q factors under normal excitations are still limited. Here, we present the realizations of quasi-BIC under normal excitation with a record Q factor up to 18 511 by engineering the symmetry properties and the number of the unit cells in all-dielectric metasurface platforms. The high-Q quasi-BICs exhibit exceptionally high conversion efficiency for the third harmonic generation and even enable the second harmonic generation in Si metasurfaces. Such ultrasharp resonances achieved in this work may immediately boost the performances of BICs in a plethora of fundamental research and device applications, e.g., cavity QED, biosensing, nanolasing, and quantum light generations.

A. Larkum, R. Orth, C. Duarte

A. Aiello, P. Banzer, M. Neugebauer et al.

M. Soskin, M. Vasnetsov

Tianyu Zhao, Ming Lei

Abstract Parallel acquisition-readout structured-illumination microscopy (PAR-SIM) was designed for high-speed raw data acquisition. By utilizing an xy-scan galvo mirror set, the raw data is projected onto different areas of the camera, enabling a fundamentally stupendous information spatial-temporal flux.

A. Greentree, C. Tahan, J. Cole et al.

The ability to conduct experiments at length scales and temperatures at which interesting and potentially useful quantum-mechanical phenomena emerge in condensed-matter or atomic systems is now commonplace. In optics, though, the weakness with which photons interact with each other makes exploring such behaviour more difficult. Here we describe an optical system that exhibits strongly correlated dynamics on a mesoscopic scale. By adding photons to a two-dimensional array of coupled optical cavities each containing a single two-level atom in the photon-blockade regime, we form dressed states, or polaritons, that are both long-lived and strongly interacting. Our results predict that at zero temperature the system will undergo a characteristic Mott insulator (excitations localized on each site) to superfluid (excitations delocalized across the lattice) quantum phase transition. Moreover, the ability to couple light to and from individual cavities of this system could be useful in the realization of tuneable quantum simulators and other quantum-mechanical devices.

W. Arnott, K. Hamasha, H. Moosmüller et al.

Soumyabrata Paul, S. Lakshmibala, V. Balakrishnan et al.

Entropic uncertainty relations (EURs) have been examined in various contexts, primarily in qubit systems, including their links with entanglement, as they subsume the Heisenberg uncertainty principle. With their genesis in the Shannon entropy, EURs find applications in quantum information and quantum optics. EURs are state-dependent, and the state has to be reconstructed from tomograms (which are histograms readily available from experiments). This is a challenge when the Hilbert space is large, as in continuous variable (CV) systems and certain hybrid quantum (HQ) systems. A viable alternative approach therefore is to extract as much information as possible about the unknown quantum state directly from appropriate tomograms. Many variants of EURs can be extracted from tomograms, even for CV systems. In earlier work we have defined many tomographic entanglement indicators (TEIs) that can be readily calculated from tomograms without knowledge of the density matrix, and have reported on their efficacy as entanglement indicators in various contexts in both CV and HQ systems. The specific objectives of the present work are as follows: (i) To use the tomographic approach to investigate the links between EURs and TEIs in CV and HQ systems as they evolve in time. (ii) To identify the TEI that most closely tracks the temporal evolution of EURs. We consider two generic systems. The first is a multilevel atom modeled as a nonlinear oscillator interacting with a quantized radiation field. The second is the Λ-atom interacting with two radiation fields. The former model accomodates investigations on the role of the initial state of the field and the ratio of the strengths of interaction and nonlinearity in the connection between TEIs and EURs. The second model opens up the possibility of examining the connection between mixed state bipartite entanglement and EURs, when the number of atomic levels is finite. Since the tomogram respects the requirements of classical probability theory, this effort also sheds light on the extent to which TEIs reflect the temporal behaviour of those EURs which are rooted in the Shannon entropy.

Brando Adranno, Olivier Renier, Guillaume Bousrez et al.

Albeit tris(8‐hydroxyquinolinato) aluminum (Alq3) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand‐centered states, the use of metal‐free 8‐hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8‐hydroxyquinolinium cations into a solid rigid network with appropriate counter‐anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as π‐stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue‐green (488 nm). Time‐dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long‐lived S1 level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq3 and related materials, both as solids and thin films with quantum yields (QYs) up to 40–50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 °C.

Martin Skenderas, Pablo Marin-Palomo, Spencer W. Jolly et al.

Asymmetric Mach-Zehnder interferometers (AMZIs) can, in principle, enable continuous wavelength tuning of a laser when used as intra-cavity filters. Their simplicity and good compatibility with generic foundry platforms are major advantages. However, the difficulty to develop a well-defined and robust control strategy is an important drawback which restricts the use-cases of these tunable lasers. Here, we make an in-depth investigation of the tunability properties of a laser including a single-stage AMZI in its cavity. We find that due to imperfections of Electro-Optic Phase Modulators (EOPMs), the dependence of the phase variation with the applied voltage is not linear. Because integrated EOPMs cannot be individually calibrated, these nonlinearities prevent a precise and independent tuning of the phase and amplitude of the AMZI transfer function, and thus continuous tuning cannot be reliably achieved. To overcome this issue, we propose a refined control strategy which allows for semi-continuous tuning. With this approach, we demonstrate a piece-wise continuous tuning of the emission wavelength by taking advantage of the coupling between amplitude and phase in the AMZI response. With our refined control strategy, we achieve tuning of the emission wavelength over the full free spectral range (FSR) of the AMZI.

Khosro Zangeneh Kamali, Lei Xu, Nikita Gagrani et al.

A rapid and programmable amplitude modulator based on the thermo-optical effect has been demonstrated by integrating transparent microheaters with metasurfaces.

Xianzhong Chen, Yu Luo, Jingjing Zhang et al.

Invisibility cloaks, which used to be confined to the realm of fiction, have now been turned into a scientific reality thanks to the enabling theoretical tools of transformation optics and conformal mapping. Inspired by those theoretical works, the experimental realization of electromagnetic invisibility cloaks has been reported at various electromagnetic frequencies. All the invisibility cloaks demonstrated thus far, however, have relied on nano- or micro-fabricated artificial composite materials with spatially varying electromagnetic properties, which limit the size of the cloaked region to a few wavelengths. Here, we report the first realization of a macroscopic volumetric invisibility cloak constructed from natural birefringent crystals. The cloak operates at visible frequencies and is capable of hiding, for a specific light polarization, three-dimensional objects of the scale of centimetres and millimetres. Our work opens avenues for future applications with macroscopic cloaking devices.

Khosravi Khorashad Larousse, Argyropoulos Christos

Localized plasmons formed in ultrathin metallic nanogaps can lead to robust absorption of incident light. Plasmonic metasurfaces based on this effect can efficiently generate energetic charge carriers, also known as hot electrons, owing to their ability to squeeze and enhance electromagnetic fields in confined subwavelength spaces. However, it is very challenging to accurately identify and quantify the dynamics of hot carriers, mainly due to their ultrafast time decay. Their nonequilibrium temperature response is one of the key factors missing to understand the short time decay and overall transient tunable absorption performance of gap-plasmon metasurfaces. Here, we systematically study the temperature dynamics of hot electrons and their transition into thermal carriers at various timescales from femto to nanoseconds by using the two-temperature model. Additionally, the hot electron temperature and generation rate threshold values are investigated by using a hydrodynamic nonlocal model approach that is more accurate when ultrathin gaps are considered. The derived temperature dependent material properties are used to study the ultrafast transient nonlinear modification in the absorption spectrum before plasmon-induced lattice heating is established leading to efficient tunable nanophotonic absorber designs. We also examine the damage threshold of these plasmonic absorbers under various pulsed laser illuminations, an important quantity to derive the ultimate input intensity limits that can be used in various emerging nonlinear optics and other tunable nanophotonic applications. The presented results elucidate the role of hot electrons in the response of gap-plasmon metasurface absorbers which can be used to design more efficient photocatalysis, photovoltaics, and photodetection devices.

Subhradeep Pal, Sumanta Gupta

In this paper, we propose a highly linear electrostatic doping (ED) assisted dual series Mach-Zehnder modulator (MZM) suitable for photonic integrated circuits (PICs). A complete simulation study on the performance of the proposed dual series MZM is incorporated in this paper. We have analytically formulated the steady-state and the nonlinear performance of the proposed modulator and the simulation results using commercial grade photonic circuit simulator are also incorporated in support of the analytical study. Simulation results show that the proposed modulator can offer <inline-formula><tex-math notation="LaTeX">$\sim\!\!16$</tex-math></inline-formula> dB of static extinction ratio (ER) with 3.2 dB of insertion loss (IL). The modulator offers approximately 10.2 dB of dynamic ER at 10 Gb/s data rate. The effect on the transfer function of the dual-series MZM due to the imbalance in the driving RF signals is also discussed supported with simulation results. The nonlinear performance of the proposed modulator is also estimated using analytical method and dual-tone test method. Results indicate that the spurious free dynamic range (SFDR) of the proposed dual series MZM for second and third order intermodulation distortions (IMD2 and IMD3) are 96.11 dB.Hz<inline-formula><tex-math notation="LaTeX">$^{1/2}$</tex-math></inline-formula>, and 132.4 dB.Hz<inline-formula><tex-math notation="LaTeX">$^{2/3}$</tex-math></inline-formula>, respectively. Study of the transient performance also reveals that the 3-dB electro-optic bandwidths are 11.39 GHz and 8.32 GHz for single and dual-series ED-assisted MZM, respectively.

Qiuqin Mao, Weiwei Zhao, Xiaoqin Qian et al.

To suppress the noise and sidelobe of photoacoustic images, a method is proposed combined with spatial coherence and polarity coherence. In this method, PA signals are delayed, multiplied, then performed polarity coherence, and finally summed. The polarity of delayed-and-multiplied signals rather than the amplitude is considered in polarity coherence operation. The polarity coherence factor is calculated based on the standard deviation of the polarity. Then, the factor as weights is applied to the coherent sum output after spatial autocorrelation to finally obtain the image. The simulated and experimental results prove that the noise level can be effectively suppressed due to its relatively low polarity coherence factor. Compared with the delay-and-sum method, the quantitative results in simulations show that the image contrast and full-width at half-maximum of the proposed method increase by about 227.0 % and 56.5 % when the signal-to-noise ratio of the raw signal is 0 dB, respectively. Besides achieving a better image contrast, this method obtains improvements in sidelobe attenuation and has a narrow main lobe.