Hasil untuk "Optics. Light"

Sheng Hsiung Chang

An ultra-broadband beam splitter is theoretically realized using a directional parallel-cascaded coupled-waveguide structure, which is designed and investigated with the effective medium method and finite-difference time-domain method. The 1 dB bandwidth is 285 nm which is ranging from 1418 nm to 1703 nm, thereby covering the optical window for long-haul communication. The electric field distributions show that there is a recoupling zone and thereby resulting in the ultra-broadband operation. The proposed beam splitter can be naturally integrated into the silicon photonic integrated circuits, thereby facilitating the applications of silicon-on-insulator waveguides.

Wen-Zhi Mao, Hong-Yi Luan, Ren-Min Ma

Abstract The diffraction limit, rooted in the wave nature of light and formalized by the Heisenberg uncertainty principle, imposes a fundamental constraint on optical resolution and device miniaturization. The recent discovery of the singular dispersion equation in dielectric media provides a rigorous, lossless framework for overcoming this barrier. Here, we demonstrate that achieving such confinement necessarily involves a new class of optical eigenmodes—narwhal-shaped wavefunctions—which emerge from the singular dispersion equation and uniquely combine global Gaussian decay with local power-law enhancement. These wavefunctions enable full-space field localization beyond conventional limits. Guided by this principle, we design and experimentally realize a three-dimensional sub-diffraction-limited cavity that supports narwhal-shaped wavefunctions, achieving an ultrasmall mode volume of 5 × 10−7 λ 3. We term this class of systems singulonic, and define the emerging field of singulonics as a new nanophotonic paradigm—establishing a platform for confining and manipulating light at deep-subwavelength scales without dissipation, enabled by the singular dispersion equation. Building on this extreme confinement, we introduce singular field microscopy: a near-field imaging technique that employs singulonic eigenmodes as intrinsically localized, background-free light sources. This enables optical imaging at a spatial resolution of λ/1000, making atomic-scale optical microscopy possible. Our findings open new frontiers for unprecedented control over light–matter interactions at the smallest possible scales.

Hamid Khan, Matiullah Khan, Yaseen Iqbal et al.

The theoretical calculations and hydrothermal techniques were adapted to explore the redshift of the TiO2 light absorption edge through Mo-doping. The band gap and reflectance curves were determined using the Kubelka-Munk transformation and the UV–Vis absorption spectra. DFT calculations revealed that doping of Mo narrowed the TiO2 band gap by creating impurity states (Mo 4d) below the conduction band. This is due to the closeness of orbital energies of Mo 4d and Ti 3d. Pinning of the Fermi level inside the conduction band verified doping of Mo in TiO2 (n-type) and boosted its absorbance within the visible light range. TiO2 nanoparticles, with and without Mo, were prepared by a hydrothermal route. Diffuse reflectance spectroscopy (DRS) data showed a systematic band gap decrease from the UV to the visible region (3.48 eV to 2.79 eV) by appropriate doping of Mo in TiO2. The experimental observations are verified by the theoretical predictions.

Sam Lin, Yixin Chen, Taeseung Hwang et al.

Active metasurfaces promise spatiotemporal control over optical wavefronts, but achieving high-speed modulation with pixel-level control has remained an unmet challenge. While local phase control can be achieved with nanoscale optical confinement, such as in plasmonic nanoparticles, the resulting electrode spacings lead to large capacitance, limiting speed. Here, we demonstrate the operation of a gigahertz-tunable metasurface for beam steering through local control of metasurface elements in a plasmonic-organic hybrid architecture. Our device comprises a corrugated metallic slot array engineered to support plasmonic quasi-bound states in the continuum (quasi-BICs). These plasmonic quasi-BICs provide ideal optical confinement and electrical characteristics for integrating organic electro-optic (OEO) materials like JRD1 and have not been previously utilized in optical metasurfaces. We obtain a quasi-static resonance tunability of 0.4 nm/V, which we leverage to steer light between three diffraction orders and achieve an electro-optic bandwidth of ~4 GHz, with the potential for further speed improvements through scaling rules. This work showcases on-chip spatiotemporal control of light at the sub-micrometer and gigahertz level, opening new possibilities for applications in 3D sensing and high-speed spatial light modulation.

Prelat Leila, Dias Eduardo J. C., García de Abajo F. Javier

The ability of surface polaritons (SPs) to enhance and manipulate light fields down to deep-subwavelength length scales enables applications in optical sensing and nonlinear optics at the nanoscale. However, the wavelength mismatch between light and SPs prevents direct optical excitation of surface-bound modes, thereby limiting the widespread development of SP-based photonics. Free electrons are a natural choice to directly excite strongly confined SPs because they can supply field components of high momentum at designated positions with subnanometer precision. Here, we theoretically explore free-electron–SP coupling mediated by small scatterers and show that low-energy electrons can efficiently excite surface modes with a maximum probability reached at an optimum surface–scatterer distance. By aligning the electron beam with a periodic array of scatterers placed near a polariton-supporting interface, in-plane Smith–Purcell emission results in the excitation of surface modes along well-defined directions. Our results support using scattering elements to excite SPs with low-energy electrons.

Jintao Liu, Li Luo, Xiangyang Yu et al.

Spectral imaging is performed primarily using reflective devices, but for transparent objects, especially transparent liquids, a transmission-based device is required to obtain more effective spectral imaging data. For this purpose, a transmitted spectral imaging data acquisition device based on a miniature multispectral spectrometer was developed and demonstrated its capability in the analysis of transparent liquids. This device allows rapid and noncontact acquisition of spectral imaging signals from transparent liquid samples. The design of the device mainly includes two parts: a shooting system and a master computer, and the optical path is optimized by selecting the appropriate diffusion plate. As an application example, a concentration-absorbance model of liquid samples at characteristic wavelengths was established and used to predict the concentrations of different liquid samples. Experimental results showed that the relative error of the predicted concentration values was within 4%, indicating excellent detection performance. Therefore, the design of the device demonstrates favorable feasibility and wide applicability in liquid detection systems.

Yuhui Liu, Weihao Lin, Fang Zhao et al.

A flexible and stable optical fiber sensor based on the Sagnac loop is proposed and experimentally demonstrated for the measurement of salinity and temperature, simultaneously. The sensing unit consists of a tapered polarization maintaining fiber (tPMF) and a fiber Bragg grating (FBG) connected in series in the Sagnac loop. The temperature response comes from the high birefringence of PMF inside Sagnac loop, and the salinity response is enabled by the high-order modes excited in the tapered area of PMF. Besides, the FBG is for temperature compensation. We have succeeded in implementing dual-parameter measurements with the sensitivities of 0.356 nm/‰ for salinity and 0.616 nm/°C for temperature, respectively. The designed sensor has the potential for long-term monitoring of real ocean states.

Lee Seojoo, Kang Ji-Hun

Owning to their unusual optical properties, such as electrical tunability and strong spatial confinement, two-dimensional surface polaritons (2DSPs) hold great promise for deep sub-wavelength manipulation of light in a reduced low-dimensional space. Control of 2DSPs is possible by using their interaction with a boundary between two media, similar to how light behaves in three-dimensional (3D) space. The understanding of the interaction in the 2D case is still in its early stages, unlike the 3D case, as in-depth investigations are only available in a few cases including the interaction of 2DSPs with structured 2D crystals. Here, we extend the scope of our understanding to the interaction of 2DSPs with metallic nano-plates on 2D crystals, focusing on the reflection of 2DSPs. Through our rigorous model, we reveal that, for strongly confined 2DSPs having much larger momentum than free space photons, the interaction results in almost total internal reflection of 2DSPs as the radiative coupling of the 2DSPs to free space is negligible. We also find that the reflection involves an anomalous phase shift dependent on the thickness of the nano-plate, due to the temporary storing of electromagnetic energy in the evanescent waves induced near the edge of the nano-plate. Our theory predicts that the phase shift saturates to an anomalous value, 0.885π, as the nano-plate becomes thicker. Our work provides a detailed understanding of how to manipulate the 2DSPs by using one of the simplest nanostructures, essential for the further development of nanostructure-integrated low-dimensional devices for polariton optics.

Zhang Liang, Jinhua Wu, Ying Cui et al.

A self-optimized single-nanowire photoluminescence thermometer allows the construction of multiple criteria for temperature measurement and chooses the best one by an automated routine based on specified optimization targets like sensitivity.

Saba Shams Lahijani, Tobias Jenke, Christian Pruner et al.

During the last decade a number of volume holographic media have been investigated that could serve not only as diffractive optical elements (DOEs) for light but also for slow neutrons. In this contribution we discuss the light optical properties of a stack of two gratings separated by an optically inert slice recorded in a Bayfol HX photopolymer. While the refractive-index modulation of the gratings for light is remarkable, the corresponding neutron optical analogue is, so far, in the medium range of other materials investigated. We therefore aim at possible improvements which are discussed in this manuscript.

Zheng Li, Yi Cheng, Jin Liu et al.

Over the past few decades, optical manipulation has emerged as a highly successful tool in various fields, such as biology, micro/nanorobotics, and physics. Among the different techniques, the transverse slot optical waveguide has shown remarkable potential in enhancing the field and significantly improving optical trapping capabilities. Additionally, microring resonators have demonstrated the ability to enhance the field at specific resonance wavelengths, enabling the manipulation and capture of particles. In this study, we investigated the impact of the structure on nanoparticle capture by introducing a 50 nm transverse slot in a 5 μm microring resonator. Through the integration of a transverse slot in the microring resonator, we observed a substantial increase in the maximum bound optical power for a nanosphere with a refractive index of 1.6 and a diameter of 50 nm, reaching 3988.8 pN/W. This value is 2292 times higher than the maximum optical force in a straight waveguide and 2.266 times higher than the maximum optical force in a microring resonator. The proposed structure significantly enhances the optical trapping capabilities for nanoscale particles, thus paving the way for the development of advanced micro/nanomanipulation techniques.

A. Grigorenko, A.K. Geim, H. Gleeson et al.

A great deal of attention has recently been focused on a new class of smart materials—so-called left-handed media—that exhibit highly unusual electromagnetic properties and promise new device applications. Left-handed materials require negative permeability µ, an extreme condition that has so far been achieved only for frequencies in the microwave to terahertz range. Extension of the approach described in ref. 7 to achieve the necessary high-frequency magnetic response in visible optics presents a formidable challenge, as no material—natural or artificial—is known to exhibit any magnetism at these frequencies. Here we report a nanofabricated medium consisting of electromagnetically coupled pairs of gold dots with geometry carefully designed at a 10-nm level. The medium exhibits a strong magnetic response at visible-light frequencies, including a band with negative µ. The magnetism arises owing to the excitation of an antisymmetric plasmon resonance. The high-frequency permeability qualitatively reveals itself via optical impedance matching. Our results demonstrate the feasibility of engineering magnetism at visible frequencies and pave the way towards magnetic and left-handed components for visible optics.

Andrey V. Panov

Metasurfaces have attracted a great deal of attention from researchers due to their prominent optical properties. In particular, metasurfaces may consist of structures possessing optical anapole resonances with strong field confinement and substantially suppressed scattering. As a result, such nanostructures display enhanced nonlinear optical properties. In this paper by means of three-dimensional finite-difference time-domain simulations, the ability of anapole modes in high-index dielectric metasurfaces with circular nanopores is shown. In the vicinity of the anapole state, the effective optical Kerr nonlinearity increases by orders of magnitude. Simultaneously, the optical transmission of the metasurface can reach high values up to unity.

Ankit Kumar Singh, Jer-Shing Huang

Fano resonance observed in various classical and quantum systems features an asymmetric spectral line shape. For designing nanoresonators for monochromatic applications, it is beneficial to describe Fano resonance in non-spectral parametric domains of critical structural parameters. We develop the analytical model of the parametric Fano profile based on a coupled harmonic oscillator (CHO) model and theoretically demonstrate its application in describing the optical response of a chirped waveguided plasmonic crystal (CWPC). The developed parametric Fano model may find applications in the design of monochromatic and spectrometer-free nanodevices.

Fan Wu, Rongzhen Jiao, Li Yu

Exploitation of strong light-matter interactions in plasmonic systems is vital for both fundamental studies and the development of new applications, which enables exceptional physical phenomena and promotes potential applications in nanophotonics, information communication, and quantum information processing. Here, we present an analytic model of the interaction between localized surface plasmon resonances and excitons, where a semiclassical method is utilized. Two kinds of metal nanoparticles (nanosphere and nanoellipsoid) are considered in our study. We derive the relations between the plasmon-exciton coupling strength and the geometry and material parameters of the coupled systems when the nanoparticles are put in an excitonic medium, which give an important guide to achieve strong plasmon-exciton coupling. Rabi splittings and anticrossing behavior are also demonstrated in the calculated extinction spectra. Furthermore, we propose an analytic model to describe the strong coupling between excitons and plasmon in a core-shell nanorod structure which is widely used in experiments. Our study provides a simple yet rigorous prescription to both analyze and design plexcitonic systems aiming at strong light-matter interactions.

George Zograf, Kseniia Baryshnikova, Mihail Petrov et al.

Resonant all‐dielectric nanophotonic structures have recently demonstrated enhancement of light emission and localization of near‐fields outside and inside the nanoresonators of various functionality. However, probing of the near‐field is still a time‐consuming and challenging procedure, requiring near‐field optical microscopy or cathodoluminescence approaches. On the contrary, inherent light emission such as Raman scattering from all‐dielectric nanostructures can provide important information on their resonant properties. Herein, probing of near‐field spatial distribution around a silicon trimer qualitatively using far‐field excitation of Raman scattering is demonstrated. The geometry of a single excitation and collection objective with lateral scanning is implemented. With this technique, switching near‐field distribution in the silicon trimer by changing the polarization of the incident light is observed. The full‐wave numerical simulations support the observed experimental results. It is believed that such an approach will be useful for near‐field probing of various all‐dielectric resonant nanostructures with a simple far‐field optical scheme.

Yury E. Geints, Igor V. Minin, Oleg V. Minin

Optical energy flow inside a dielectric microsphere is usually codirected with the optical wavevector. At the same time, if the optical field in a microsphere is in resonance with one of the high-quality spatial eigenmodes (whispering-gallery modes - WGMs), a region of reverse energy flow emerges in the shadow hemisphere. This area is of considerable practical interest due to increased optical trapping potential. In this Letter, we consider a perforated microsphere with an air-filled single pinhole fabricated along the particle diameter and numerically analyze the peculiarities of WGM excitation in a nanostructured microsphere. A pinhole isolates the energy backflow region of a resonant mode and changes a perforated microsphere into an efficient optical tweezer. For the first time to our knowledge, we reveal the multiple enhancement of backflow intensity in the pinhole at a WGM resonance and discuss the way for its manipulation.

Adam Lešundák, Tuan M. Pham, Martin Čížek et al.

We demonstrate an optical frequency analysis method using the Fourier transform of detection times of fluorescence photons emitted from a single trapped 40Ca+ ion. The response of the detected photon rate to the relative laser frequency deviations is recorded within the slope of a dark resonance formed in the lambda-type energy level scheme corresponding to two optical dipole transitions. This approach enhances the sensitivity to the small frequency deviations and does so with reciprocal dependence on the fluorescence rate. The employed lasers are phase locked to an optical frequency comb, which allows for precise calibration of optical frequency analysis by deterministic modulation of the analyzed laser beam with respect to the reference beam. The attainable high signal-to-noise ratios of up to a MHz range of modulation deviations and up to a hundred kHz modulation frequencies promise the applicability of the presented results in a broad range of optical spectroscopic applications.

Hui-Chao Zhou, Ningbo Chen, Huangxuan Zhao et al.

Monitoring the changes in tumor vascularity is important for anti-angiogenic therapy assessment with therapeutic implications. However, monitoring vascularity is quite challenging due to the lack of appropriate imaging techniques. Here, we describe a non-invasive imaging technique using optical-resolution photoacoustic microscopy (OR-PAM) to track vascular changes in prostate cancer treated with an anti-angiogenic agent, DC101, on a mouse ear xenograft model. Approximately 1–3 days after the initial therapy, OR-PAM imaging detected tumor vascular changes such as reduced vessel tortuosity, decreased vessel diameter and homogenized intratumoral vessel distribution. These observations indicated vessel normalization, which was pathologically validated as increased fractional pericyte coverage, functional perfusion and drug delivery of the vessels. After four DC101 interventions, OR-PAM imaging eventually revealed intratumoral vessel regression. Therefore, OR-PAM imaging of the vasculature offers a promising method to study anti-angiogenic drug mechanisms of action in vivo and holds potential in monitoring and guiding anti-angiogenic therapy. Keywords: Optical-resolution photoacoustic microscopy, Tumor, Anti-angiogenesis, Vasculature, Vascular normalization

Bihui Zhu, Jamir Marino, Norman Y Yao et al.

The Dicke model—a paradigmatic example of superradiance in quantum optics—describes an ensemble of atoms which are collectively coupled to a leaky cavity mode. As a result of the cooperative nature of these interactions, the system’s dynamics is captured by the behavior of a single mean-field, collective spin. In this mean-field limit, it has recently been shown that the interplay between photon losses and periodic driving of light–matter coupling can lead to time-crystalline-like behavior of the collective spin (Gong et al 2018 Phys. Rev. Lett. 120 040404). In this work, we investigate whether such a Dicke time crystal (TC) is stable to perturbations that explicitly break the mean-field solvability of the conventional Dicke model. In particular, we consider the addition of short-range interactions between the atoms which breaks the collective coupling and leads to complex many-body dynamics. In this context, the interplay between periodic driving, dissipation and interactions yields a rich set of dynamical responses, including long-lived and metastable Dicke-TCs, where losses can cool down the many-body heating resulting from the continuous pump of energy from the periodic drive. Specifically, when the additional short-range interactions are ferromagnetic, we observe time crystalline behavior at non-perturbative values of the coupling strength, suggesting the possible existence of stable dynamical order in a driven-dissipative quantum many-body system. These findings illustrate the rich nature of novel dynamical responses with many-body character in quantum optics platforms.