查看更多>>摘要：Extending the length of femtosecond laser filament has always been desired for related atmospheric applications. Here we demonstrated that significant extension of filament can be achieved in air by using phase-nested beam which integrates the arise of filamentation and longitudinally extended background reservior in one optical beam. The influences of beam parameters on the length and uniformity of filament and corresponding physical mechanism are revealed. The energy extraction process from the background reservoir to the filament is investigated based on the evolution of pulse profile during the regeneration of filament. A fiber-like model is proposed to explain the capture effect of filament to the background reservior. Our theoretical results will be helpful to understand the mechanism of background reservior in the extending of filament, and may further guide the experimental design of phase-nested beam to achieve long and homogeneous filament in air.
查看更多>>摘要：Three-color ultrabroadband coherent anti-Stokes Raman scattering (CARS) spectroscopy in the range of 400-3500 cm-1 based on a single fiber laser is demonstrated. A 400-fs supercontinuum (SC) with spectral bandwidth between 780 and 1240 nm was generated in a facile manner, by launching 280-fs pulses from the fiber laser into an all-normal-dispersion photonic crystal fiber (PCF) with subsequent compression using a grating pair. It implements a device that can capture the CARS signal of most of the fingerprint range in real time and has a high signal-to-noise ratio. Furthermore, thanks to the excellent temporal overlap of its broad spectrum, the SC was used as both pump and Stokes in three-color broadband CARS (BCARS) spectroscopy of benzonitrile. Nine Raman modes of benzonitrile in the 400-3500 cm-1 range were detected simultaneously.
查看更多>>摘要：Three-dimensional light field display has achieved an impressive result and is a great potential display method. To provide real-world dense views efficiently, many virtual view synthesis approaches have been proposed. However, previous methods are not robust enough when the input view poses with a wider baseline or large rotation. Here, a virtual view synthesis method based on feature reprojection and fusion is presented, which can robustly generate high-quality dense virtual views for 3D light-field display. The target view depth map is generated with our proposed unsupervised network, which provides the 3D scene distribution priori. Then input views' feature maps are reprojected to the target view position. To fuse these reprojected feature maps effectively, a feature fusion Transformer network is designed, which encodes all input views' information and generates a fused feature map to represent the target view implicitly. The target view color map can be synthesized by rendering the fused feature map. Experimental results demonstrate the effectiveness of the proposed method, which shows outstanding performances when the input view poses are arranged unregularly. We believe the proposed method relieves the requirements of input sparse views acquisition and contributes to the wide applications of 3D light-field display in the future.
查看更多>>摘要：The structure proposed in this paper is composed of an outer circular ring resonator (CRR) and four L-shaped resonators (LSRs) in the middle. The destructive interference between bright modes produces a broadband electromagnetically induced transparency (EIT) with a maximum transmission efficiency of 97.6% in both vertical polarization directions. The field distributions and the three-level lambda-type system clarify the physical mechanism of the coupling process between bright modes. The calculated transmission spectrum based on the two-particle model is consistent with the simulated transmission spectrum, which proves the correctness of the results. By introducing hybridization bandgap (HBG) to the structure, the bandwidth of EIT-like effect expands. This structure has a fourfold (C4) rotational symmetry; thus, it is insensitive to the polarization angle. In addition, the transparency window undergoes a redshift as the Fermi energy of Dirac semimetal decreases. Meanwhile, the group delay is also controlled. Due to the wide bandwidth, a large delay bandwidth product (DBP) is obtained. Our work provides a new method for the production of slow-light devices and broadband filters.
查看更多>>摘要：The propagation characteristics of elliptical Airy vortex beams (EAVB) with different elliptical parameter and topological charges are demonstrated experimentally and numerically. Besides, the relationship between elliptical parameter and detection probability of the orbital angular momentum(OAM) is analyzed numerically. The results show that elliptical parameter has a significant impact on the OAM spectral distribution and the propagation characteristics of the EAVB. The EAVB possess an elliptical shaped transverse pattern in the main lobe surrounded by a series of rings and has the line of intensity nulls in the focal plane. It also has two focal planes during the propagation, and the distance between the two focal plane becomes shorter with the increase of elliptical parameter. The long axis of the intensity ellipse of the EVAB rotates 90 between the second focal plane and the first focal plane. There is a linear relationship between OAM detection probability and the elliptical parameter. The experimental results are in good agreement with theory, which will be helpful for the application of EAVB in optical trapping and optical communication.
查看更多>>摘要：Plasmonic nanoparticles are emerging as the crucial components for photodetector, biosensor, solar cell, and laser, primarily by virtue of localized surface plasmon assisted Forster Resonance Energy Transfer (FRET) and the electric field amplification at nanoscale. The present work extends multipole spectral expansion approach to treat energy transfer interactions and the electric field in the presence of a metallic spheroidal nanoparticle. The energy transfer rate enhancement and the electric field enhancement are expressed in the form of closed form expressions. These expressions are used to identify and quantify the role of aspect ratio and embedding medium on these processes. The observed multiple resonance peaks in the spectra and also their spectral shift is explained on the basis of closed form expressions. The FRET based refractive-index sensor is reported to show sensitivity (S) ~511.8 nm/RIU. The approach and the closed form expressions developed in the present work can be used for designing plasmonic systems.
查看更多>>摘要：In free space optical (FSO) communication, atmospheric turbulence will introduce aberration to the laser wavefront, which will reduce the coupling efficiency of space light to optical fiber. The system based on blind optimization principle can realize wavefront aberration compensation by using actuators such as fast steering mirror (FSM) and deformable mirror (DM), combined with blind optimization control algorithms. Stochastic parallel gradient descent (SPGD) algorithm is widely used in this kind of system. The disadvantages of SPGD algorithm are possibly local convergence and slow convergence. In order to improve the convergence performance of the SPGD algorithm, we proposed improved SPGD algorithms called Adagrad & Staged SPGD algorithm (AS-SPGD). Specifically, to accelerate SPGD algorithm, the Adagrad SPGD algorithm (A-SPGD) integrated Adagrad's adaptive gain strategy is proposed firstly in wavefront tip-tilt aberration compensation using FSM. Then, we consider compensating the wavefront high-order aberration using DM. By adopting the strategy of using SPGD algorithm with different settings in different stages, the Staged SPGD algorithm (S-SPGD) is proposed to improve the local convergence of the traditional SPGD algorithm. The simulation results show that the Adagrad SPGD algorithm converges faster than the traditional SPGD algorithm in the compensation of tip-tilt aberrations of different amplitude; the Staged SPGD algorithm has better global convergence ability than the traditional SPGD algorithm in high-order aberration compensation.
Breiby, Dag WernerHussain, NazabatHasanzade, Mojde
10页
查看更多>>摘要：Microscopy is going through a digital renaissance and new schemes are developed where computer and algorithms constitute an integral part of the imaging process itself. Computational microscopy increases performance by offering better resolution, larger field of view, quantitative contrast and also reduced size, weight and economic cost. Fourier Ptychographic microscopy utilizes multiple images of a sample taken at lower resolution, each illuminated with a unique incidence angle coherent source, and synthesizes one high resolution complex valued image by iterative phase retrieval algorithms. The recorded images are often corrupted with background noise and pre-processing is needed to improve the quality of the FP recovered image. The pre-processing involves data denoising, thresholding and intensity balancing. We have investigated different wavelet families to test their performance in terms of having compact support and giving the desired level of decomposition for optimal intensity thresholding and denoising in Fourier Ptychography (FP). The wavelet families Daubechies, Biorthogonal, Reverse Biorthogonal, Coiflet, Fejer-Korovkin, Discrete Meyer and Symlet with different compact support have been studied. The obtained threshold was used with noisy synthetic and experimental images for a variety of objects to evaluate the performance of the described framework. In particular, Reverse Biorthogonal wavelets were found to preserve useful signal in corrupted images to a great extent (RMS error 0.39) with low computational cost. Consequently, quantitatively more correct amplitude and phase images with uniform and homogeneous background could be recovered.
查看更多>>摘要：In this paper, a high-efficient reflective polarization converter based on all-metal stereostructured anisotropic metamaterials (AMMs) in terahertz (THz) region was proposed and investigated numerically. The unit-cell structure of the converter is assembled by vertical metallic double L-shaped stereostructures (DLSSs) adhered on the ground plane. The simulated results show that the proposed stereostructured AMMs can convert the incident x/y-polarized (x/y-pol.) wave into the right/left-handed circular polarization (RCP/LCP) wave, y/x-polarized (y/x-pol.) wave, and left/right-handed circular polarization (LCP/RCP) wave at 1.37 THz, 1.45 THz and 1.54 THz, respectively. Furthermore, the high-efficient polarization conversion of the proposed AMMs can be sustained within a wide incident angle from 0 to 75 for both transverse electric (TE) and transverse magnetic (TM) modes. The physical mechanisms of the observed polarization conversion are elucidated by taking advantage of surface current distributions. The further simulation results indicate that the operation frequency can be adjusted by changing the geometric parameters of the DLSSs. The proposed stereostructured AMMs-based reflective polarization converter can find potential THz applications, such as remote sensors, imaging systems, and reflector antennas.
查看更多>>摘要：Visible light communication (VLC) allows low-cost, simple and flexible optical wireless communication (OWC) transmission. In this work, we put forward and demonstrate for the first time 100 m non-flickering image sensor based VLC using under-sampled phase shift on-off keying (UPSOOK) and 6-bit 4-light-emitting-diode (LED) spatial modulation. As each light emitting diode (LED) can provide three well distinguished intensity states, 6-bit data can be realized by using only 4 LEDs in the vehicle rear lamps. Bit-error-rate (BER) measurements at different camera ISO values are also studies. Experimental results show that 130 m long distance 120 bit/s image sensor based VLC system can be achieved using a single white-LED at ISO = 800. Results also show that 100 m long distance 720 bit/s image sensor based VLC system can be realized using 4 LEDs at ISO = 800. Both results satisfy the pre-forward error correction BER (pre-FEC, BER = 3.8 x 10(-3)).
NSTL
Elsevier