Hasil untuk "Optics. Light"

E. Marcatili

Chunsheng Zhang, Tingnuo Pan, Xiao Zhang et al.

Coding metasurfaces (CMs) exhibit powerful capabilities in manipulating electromagnetic waves. Although conventional CMs are capable of manipulating both linearly polarized (LP) and circularly polarized (CP) waves, the Pancharatnam–Berry phase methods for controlling CP waves lead to inherent limitations, such as the inability to independently manipulate copolarized components and the functional locking between the two orthogonal CP waves. Herein, a tunable multifunctional terahertz (THz) metasurface integrated with vanadium dioxide (VO2) is demonstrated to manipulate LP waves by the propagation phase and CP waves by hybrid phase. The required phase profiles are obtained by changing the length of the VO2, the cross‐shaped ellipse, and its rotation angle separately. The proposed design strategy can overcome the above limitations at different frequencies. As a proof‐of‐concept demonstration, four metasurfaces are constructed to achieve dynamic switching between dual‐beam and single‐beam by the insulator–metal phase transition of VO2, as well as anomalous reflection, vortex beams, focused vortex beams, and absorber regardless of the insulating and metallic state of VO2. This multifunctional CM has great potential in THz wireless communications.

Li Zhang, Feiyue Lu, Zhiwen Liang et al.

Phonon polaritons (PhPs) in polar crystals have garnered extensive attention due to their excellent characteristics in light‐matter interaction. However, wavelength and frequency band of PhPs are currently quite narrow and heavily dependant on phonon reststrahlen bands of material chosen. In most cases, these reststrahlen bands cannot be fully occupied. Moreover, methods for tuning and manipulating PhPs are rather limited. Herein, an idea of curvature and dielectric is introduced to tune properties of surface phonon polaritons (SPhPs) in quasi‐1‐dimensional complementary nanostructures: nanowire (NW) and nanohole (NH). Numerical results of wurtzite AlN and cubic SiC show that dispersive spectrum of SPhPs can be effectively regulated by curvature and dielectric methods. NH complements frequency band range of SPhP modes of NW structures. NW together with NH accurately occupy the whole reststrahlen band of SPhPs of semiconductors. Furthermore, the frequency‐band subinterval of SPhP in NHs and NWs can be significantly tuned by dielectric. The SPhP dispersion spectrum and wavelength compression ratio in NW and NH structures are inherently self‐consistent. Moreover, calculated results are in good agreement with relevant experimental data. Herein, new ideas are provided for the regulation and manipulation of PhPs in nanostructures.

Samalla Krishna, Kumar P. Naveen, Subba Rao S.P.V. et al.

Free Space Optics is a form of Optical Wireless communication technique that uses free space as a medium between transmitter and receveur. It is especially useful for short range point-to-point communication links when a physical communication connections is not economical and feasible. In light of the benefits a FSO can offer, there has been a significant increase of interest in research community to develop efficient FSO transmitter and receveur system. This work is focused on the développent of efficient communication link for optical sources with very low Pulse- Répétition-Frequency. The main contribution of this work is the développent of simple yet efficient alternatives to the traditional topics of FSO design like PPM Modulation, Synchronisation etc.

Shun Hashiyada, An'an Wu, Yoshito Y. Tanaka

Chiral light-matter interactions have traditionally been understood in terms of electric-magnetic dipolar interference driven by light with spin angular momentum. Here, we show that optical chirality can also originate from the orbital angular momentum (OAM) of light, giving rise to higher-order multipolar chiral responses. Using a twisted gold nanorod dimer and tightly focused circularly polarized optical vortex beams carrying spin and orbital angular momenta of the same sign, we measure spectrally and spatially resolved chiral dichroism signals that persist even where spin optical chirality vanishes, revealing a quadrupole-mediated chiral interaction driven by OAM. The spectra reveal clear quadrupole resonances whose spectral profile is strongly modulated by the OAM sign, demonstrating an OAM-driven chiral interaction. Crucially, the signal satisfies optical reciprocity, ruling out artefacts from anisotropy or misalignment and confirming its nature as a true chiral response. Angular momentum dissipation analysis further shows that orbital contributions dominate over spin. These findings establish the existence of a distinct form of optical chirality, referred to as orbital optical chirality, which opens new avenues for probing and controlling multipolar chiral light-matter interactions beyond the dipolar paradigm.

Andrew T Meek, Franziska Busse, Nils M Kronenberg et al.

Mechanical forces and stiffness play key roles in the health and development of cells and tissue, but despite the physical connection between these quantities, they cannot be monitored in parallel in most cases. Here, we introduce a fully integrated microscope that combines a method for high-resolution cell force imaging (elastic resonator interference stress microscopy, ERISM) with non-contact mapping of the elastic properties of cells (via Brillouin microscopy). In order to integrate both techniques, we had to account for the strong back reflection on the surface of the microcavity used for ERISM measurements as well as the local destruction of the cavity under illumination for Brillouin microscopy measurements. Therefore, we developed an elastic optical microcavity with minimal absorption that can perform ERISM measurements without sustaining laser damage during Brillouin microscopy. Furthermore, an unequal-arm Michelson interferometer was designed to suppress the back reflection of the laser on the ERISM microcavity surface using division by amplitude interference to reduce the reflected light and enhance the Brillouin signal. We show the utility of our integrated microscope by simultaneously mapping cellular forces and Brillouin shifts in cultures of fibroblast cells.

Hanojhan Rajahrajasingh, Dushantha Nalin K. Jayakody

This paper investigates the performance of dual-hop unmanned aerial vehicle (UAV)-assisted communication channels, employing a decode-and-forward (DF) relay architecture. The system leverages terahertz (THz) communication for the primary hop and visible light communication (VLC) for the secondary hop. We conduct an in-depth analysis by deriving closed-form expressions for the end-to-end (E2E) bit error rate (BER). Additionally, we use a Monte Carlo simulation approach to generate best-fitting curves, validating our analytical expressions. A performance evaluation through BER and outage probability metrics demonstrates the effectiveness of the proposed system. Specifically, our results indicate that the proposed system outperforms Free-Space Optics (FSO)-VLC and Radio-Frequency (RF)-VLC at a higher signal-to-noise ratio (SNR). The results of this study provide valuable insights into the feasibility and limitations of UAV-assisted THz-VLC communication systems.

Neptune Baro, Partha Pratim Mondal

We report the realization of the first planar optical tweezer trap system by a sheet of light. To visualize the trapping of the target object (dielectric bead or live cell) in a plane, an orthogonal widefield detection is employed. The planar / two-dimensional lightsheet optical tweezer (2D-LOT) sub-system is realized in an inverted microscopy mode with illumination from the bottom. A 1064 nm laser (power $\sim 500 mW$) is expanded and directed to a combination of cylindrical lens and high NA objective lens to generate a tightly-focused diffraction-limited light sheet. The object to be trapped is injected in the specimen chamber (consists of two coverslips placed at a distance of $\approx 1~mm$) using a syringe. The illumination of trap-laser light is along Z-direction (with coverslip along XZ-plane) whereas, the detection is achieved perpendicular to the coverslip (along Y-axis). The orthogonal detection is employed to directly visualize the trapping in a plane. The characterization of system PSF estimates the size of light sheet trap PSF to be, $2073.84 ~μm^2$ which defines the active trap region / area. Beads are tracked on their way to the trap region for determining the trap stiffness along Z and X i.e, $k_z = 1.13 \pm 0.034 ~pN/μm$ and $k_x = 0.74 \pm 0.021 ~pN/ μm$. Results (image and video) show real-time trapping of dielectric beads in the trap zone (2D plane) generated by the light sheet. The beads can be seen getting trapped from all directions in the XZ-plane. Prolonged exposure to the light sheet builds up a 2D array of beads in the trap zone. Similar experiments on live NIH3T3 cells show cells trapped in the 2D trap. The potential of the planar trap lies in its ability to confine objects in two dimensions, thereby opening new kinds of experiments in biophysics, atomic physics, and optical physics.

Hongwei Jia, Mudi Wang, Shaojie Ma et al.

Abstract Chiral zeroth Landau levels are topologically protected bulk states. In particle physics and condensed matter physics, the chiral zeroth Landau level plays a significant role in breaking chiral symmetry and gives rise to the chiral anomaly. Previous experimental works on such chiral Landau levels are mainly based on three-dimensional Weyl degeneracies coupled with axial magnetic fields. Their realizations using two-dimensional Dirac point systems, being more promising for future applications, were never experimentally realized before. Here we propose an experimental scheme for realizing chiral Landau levels in a two-dimensional photonic system. By introducing an inhomogeneous effective mass through breaking local parity-inversion symmetries, a synthetic in-plane magnetic field is generated and coupled with the Dirac quasi-particles. Consequently, the zeroth-order chiral Landau levels can be induced, and the one-way propagation characteristics are experimentally observed. In addition, the robust transport of the chiral zeroth mode against defects in the system is also experimentally tested. Our system provides a new pathway for the realization of chiral Landau levels in two-dimensional Dirac cone systems, and may potentially be applied in device designs utilizing the chiral response and transport robustness.

Y. Inouye, S. Kawata

C. Ahrens, Henson Robert

Yadgar Hussein Shwan

The current work includes measurements of the resonance angle and reflectance for p-polarization of the electric field by using the Fresnel equation at a given length. Gold's surface plasmon wave can be seen at the metal-to-air boundary. We try to determine the greatest (SPR) angle for a metal thin layer that is most suitable for the surface plasmon excitation while stimulated by a  laser. SPR was performed of a  single film of gold placed on a glass prism; there are SPR modes in this structure, which match the surface plasmon. We also suggest that the SPR mode associated with the Au surface, which is extremely sensitive to changes in the surrounding environment, particularly (dielectric). A few considerations to be taken into account to attain the SPR, like the incident angle of light rays addressed and analyzed for the purpose of finding the essential value for the plasmon to be emerge; the gold/air resonance angle. Furthermore, we can compare our result with other work, which was performed by using the Finite-Element-Method (FEM), the simulation is done by FDTD (Finite Difference Time Domain) software. SPR was applied in a variety of domains, containing biomedicine science, optics, biomedicine, photo-thermal plasmon, and health.

Federico Tommasi, Lorenzo Fini, Stefano Focardi et al.

Abstract Random walks are common in nature and are at the basis of many different phenomena that span from neutrons and light scattering to the behaviour of animals. Despite the evident differences among all these phenomena, theory predicts that they all share a common fascinating feature known as Invariance Property (IP). In a nutshell, IP means that the mean length of the total path of a random walker inside a closed domain is fixed by the geometry and size of the medium. Such a property has been demonstrated to hold not only in optics, but recently also in the field of biology, by studying the movement of bacteria. However, the range of validity of such a universal property, strictly linked to the fulfilment of equilibrium conditions and to the statistical distributions of the steps of the random walkers, is not trivial and needs to be studied in different contexts, such as in the case of biological entities occupied in random foraging in an open environment. Hence, in this paper the IP in a virtual medium inside an open environment has been studied by using actual movements of animals recorded in nature. In particular, we analysed the behaviour of a grazer mollusc, the chiton Acanthopleura granulata. The results depart from those predicted by the IP when the dimension of the medium increases. Such findings are framed in both the condition of nonequilibrium of the walkers, which is typical of animals in nature, and the characteristics of actual animal movements.

Wen Lei, Zhe Chen, Yongzhe Xu et al.

Charging batteries in underwater scenarios is generally very expensive and impractical, and solar cell (SC)-based underwater simultaneous lightwave information and power transfer (SLIPT) systems are a powerful solution. However, silicon SC receiver devices have limited bandwidth and are prone to deep signal-to-noise (SNR) degradation during underwater light fading effects. For these problems, this manuscript proposes a negative-biased SC optical receiver scheme to increase the <inline-formula><tex-math notation="LaTeX">$-3$</tex-math></inline-formula> dB bandwidth of silicon SC from 440 kHz to 780 kHz. For the deep fading of SNR caused by various degradation effects in the water environment, a low peak average power ratio (PAPR) discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) modulation scheme is employed to counteract the deep fading phenomenon in the system. Achieved a communication rate of 15.2 Mbps in a 60 cm underwater environment with a fading factor of 0.403 and a bit error rate (BER) of <inline-formula><tex-math notation="LaTeX">$1.59\times 10^{-3}$</tex-math></inline-formula> under perturbation. Also, the performance of DFT-S-OFDM and orthogonal frequency division multiplexing (OFDM) modulation systems in water environments with different turbidity (absorption characteristics and scattering) and presence of disturbances are compared separately, and the DFT-S-OFDM system is more robust. Finally, we complete the energy harvesting during the communication process, and the experiments show that the total battery power efficiency of the energy harvesting system can be increased by 1.87 times under the white light-emitting diode (LED) continuous irradiation for three hours.

Ali Golestani, Alex O. C. Davis, Filip Sośnicki et al.

The power spectrum of an optical field can be acquired without a spectrally resolving detector by means of Fourier-transform spectrometry, based on measuring the temporal autocorrelation of the optical field. Analogously, we here perform temporal envelope measurements of ultrashort optical pulses without time resolved detection. We introduce the technique of Fourier transform chronometry, where the temporal envelope is acquired by measuring the frequency autocorrelation of the optical field in a linear interferometer. We apply our technique, which is the time-frequency conjugate measurement to Fourier-transform spectrometry, to experimentally measure the pulse envelope of classical and single photon light pulses.

Xialin Liu, Boris Braverman, Robert W. Boyd

High-speed spatial light modulators (SLM) are crucial components for free-space communication and structured illumination imaging. Current approaches for dynamical spatial mode generation, such as liquid crystal SLMs or digital micromirror devices, are limited to a maximum pattern refresh rate of 10 kHz and have a low damage threshold. We demonstrate that arbitrary spatial profiles in a laser pulse can be generated by mapping the temporal radio-frequency (RF) waveform sent to an acousto-optic modulator (AOM) onto the optical field. We find that the fidelity of the SLM performance can be improved through numerical optimization of the RF waveform to overcome the nonlinear effect of AOM. An AOM can thus be used as a 1-dimensional SLM, a technique we call acousto-optic spatial light modulator (AO-SLM), which has 50 um pixel pitch, over 1 MHz update rate, and high damage threshold. We simulate the application of AO-SLM to single-pixel imaging, which can reconstruct a 32x32 pixel complex object at a rate of 11.6 kHz with 98% fidelity.

Yuanbin Jin, Jiangwei Yan, Shah Jee Rahman et al.

We experimentally study the interference of dipole scattered light from two optically levitated nanoparticles in vacuum, which present an environment free of particle-substrate interactions. We illuminate the two trapped nanoparticles with a linearly polarized probe beam orthogonal to the propagation of the trapping laser beams. The scattered light from the nanoparticles are collected by a high numerical aperture (NA) objective lens and imaged. The interference fringes from the scattered vector light for the different dipole orientations in image and Fourier space are observed. Especially, the interference fringes of two scattered light fields with polarization vortex show the π shift of the interference fringes between inside and outside the center region of the two nanoparticles in the image space. As far as we know, this is the first experimental observation of the interference of scattered vector light fields from two dipoles in free space. This work also provides a simple and direct method to determine the spatial scales between optically levitated nanoparticles by the interference fringes.

Liu Wenzhe, Liu Wei, Shi Lei et al.

Polarization singularities of vectorial electromagnetic fields locate at the positions where properties of polarization ellipses are not defined. First observed for conical diffraction in 1830s, polarization singularities have been studied systematically with the underlying concepts being reshaped and deepened by many pioneers of wave optics. Here we review the recent results on the generation and observation of polarization singularities in metaphotonics. We start with the discussion of polarization singularities in the Mie theory, where both electric and magnetic multipoles are explored from perspectives of local and global polarization properties. We then proceed with the discussion of various photonic-crystal structures, for which both near- and far-field patterns manifest diverse polarization singularities characterized by the integer Poincaré or more general half-integer Hopf indices (topological charges). Next, we review the most recent studies of conversions from polarization to phase singularities in scalar wave optics, demonstrating how bound states in the continuum can be exploited to generate directly optical vortices of various charges. Throughout our paper, we discuss and highlight several fundamental concepts and demonstrate their close connections and special links to metaphotonics. We believe polarization singularities can provide novel perspectives for light-matter manipulation for both fundamental studies and their practical applications.

Lina Fan, Yi Li, Wenqing Zhao et al.

Phase-change materials (PCMs) have become as promising elements in silicon photonic systems. We propose an optical buffer device based on vanadium dioxide (VO₂) embedded on silicon-on-insulator waveguides with a microring resonator. The upload straight waveguide is for coupling light signal from the input port into VO₂ embedded on microring resonator and the download straight waveguide with VO₂ films is for coupling the storage signal to the output port. The optical characteristics of optical buffer device under different structural parameters are analyzed by using finite difference mode simulation (MODE). By controlling the phase state of VO₂ in two coupling regions, the buffer speed of the device can be up to 0.5 ps and buffer time up to 78.28 ps. The optical buffer based on VO₂ is a new way for PCM optical buffer.

Tsendsuren Khurelbaatar, Je-Hoi Mun, Jaeuk Heo et al.

Energetic, few-fs pulses in the deep-UV region are highly desirable for exploring ultrafast processes on their natural time scales, especially in molecules. The deep-UV source can be generated from gas media irradiated with few-cycle near-infrared laser pulses via a third-order frequency conversion process, which is a perturbative mechanism in a relatively weak field regime. In this work, we demonstrate that the deep-UV generation process is significantly affected by also even higher nonlinear processes, such as the ionization depletion of gas and plasma-induced spatiotemporal distortion of propagating light. In the experiment, by optimizing the deep-UV (3.6–5.7 eV) generation efficiency, the highest deep-UV energy of 1 μJ was observed from a moderately ionized 0.8-bar Ar gas target. The observed UV spectra exhibited frequency shifts depending on the experimental conditions—gas type, gas pressure, and the gas cell location—supporting the importance of the highly nonlinear mechanisms. The experimental observations were well corroborated by numerical simulations.