查看更多>>摘要：Based on the geometric phase theory, a broadband terahertz wave vortex beam generator based on a transmissive plasmonic metasurface is proposed. The metasurface is composed of rectangular holes on a gold film. By deriving the relationship between the unit rotation angle and azimuth angle, arranging the rectangular holes can generate vortex beams with different topological charges. In this paper, three vortex phase plates with different topological charges are designed. The performance of metasurface vortex beam generators under normal incidence of circularly polarized beams is analyzed and discussed. In the bandwidth range of 2 THz- 3 THz, the transmission efficiency can reach about 24%. The designed device is close to the transmission limit of a single-layer transmissive metasurface.
查看更多>>摘要：In this work, the theoretical relationship model between the incident polarization phase and transverse spin splitting (TSS) shifts of photonic spin Hall effect (PSHE) is established. Based on the established model, the effect of the incident polarization phase on the TSS is systematically studied, and several characteristic laws are summarized. These findings can help people better understand PSHE. In addition, it is found that, no matter what the incident angle and polarization angle are, the TSS shift at polarization phase equal to +/- 90 degrees is larger than that at other polarization phases. It can even reach several microns under certain incident angle and polarization angle, and is almost an order of magnitude larger than the usual TSS shift, which is generally tens to hundreds of nanometers. This provides a new way for enhancing PSHE. Furthermore, when the polarization phase is 90 degrees or -90 degrees, under a certain polarization angle, slightly adjust the polarization angle, the TSS shift will change sharply and its direction will be reversed. This interesting finding has great application value in the field of photon manipulation.
查看更多>>摘要：We propose a spatial division multiplexing scheme based on the Bessel-Gaussian Schell-mode beam. Such a communication scheme can enhance the capacity of free-space optical communication (FSO) in turbulence. This multiplexing utilizes the relationship between the characteristics of coherence degree distribution and the distant facula, realizing the separation of several BGSM beams with different Bessel parameter from each other, which makes the multiplexing technique deploying coherence modulation possible. The advantage of this scheme is its resistance to the atmospheric influence which exists widely in the optical wireless communication's application environment. According to the simulation, for the transmission length of about 1300 m, under the weak turbulence environment (C-n(2) = 10(-16) m(2/3)), the BGSM-SDM scheme can support about 5 times more capacity compared with the traditional optical wireless communication scheme with Gaussian beam, and while the turbulence becomes strong (C-n(2) = 10(-13) m(2/3)), the SDM scheme degenerates to single channel because of the beam expansion, but it can still support more than 2 times more capacity. The scheme is proved work stable for each channel, and applicable in strong turbulent environment by measuring the signal and noise in the experiment. I believe it provides a promising choice for the future 6G ultrahigh-speed wireless communication.
查看更多>>摘要：Laser reflective tomography imaging (LRTI) is unique in the remote sensing of space targets because the resolution is independent of the distance. As it is usually difficult to obtain the 360-degree of reflectance projections, the estimation of the proper sampling interval and sampling angle becomes a key problem. In this paper, we conducted an LRTI experiment with a distance of 0.98-km and a wavelength of 1064 nm, and constructed three targets with typical shapes, namely, planar target, plane combination target, and closed surface target. By comparing the evaluation indexes of retrieved images, the following was found: (1) When the sampling interval exceeds the maximum sampling interval derived by the Nyquist sampling law, the quality of reconstructed images deteriorates rapidly; (2) When the sampling angle is greater than 70 degrees and 90 degrees, the image of planar and plane combination target can be reconstructed excellently, respectively. However, contour image reconstruction requires full angle projection for closed-surface target; (3) When the sampling angle is fixed, the quality of reconstructed image is best for the vertical detection. This paper determines the limiting conditions of the sampling interval and sampling angle, which are of great practical significance in guiding the space-borne LRTI in sensing the space target with a long distance.
查看更多>>摘要：The sensitivity of Fabry-Perot (FP) sensor is determined by the change of cavity length. To achieve high sensitivity, we employ supercontraction property of spider dragline silk (SDS) to fabricate a FP cavity, and the length of the cavity can change up to 99.9% of the initial cavity length. The cavity consists of two reflecting surfaces which are the fiber end and the glass plane coated with gold. These two reflecting surfaces are connected by 1 cm long SDS, and the initial length of the FP cavity is 2 mm. Supercontraction property enables SDS shrink axially in length under high relative humidity (RH) environment, shrinking SDS pulls two reflecting surfaces closer to each other, so that the cavity length decreases and the free spectral range (FSR) of interference spectrum increases when environmental RH is more than 68%. Thus the proposed FP cavity length is adjustable with the change of RH, and it can change dramatically in the high humidity. FSR of the obtained spectrum can change from 0.600 nm to 466.538 nm when the RH increases from 68%RH to 95%RH. The experimental results indicate that the average sensitivity of the proposed SDS-based sensor is 27.355 nm/%RH in the range of 78%RH-95%RH, and the maximum sensitivity is 266.825 nm/%RH when RH increases from 94%RH to 95%RH. Supercontraction property makes SDS have the potential for RH sensing in high humidity range with high sensitivity. The proposed humidity sensor works only when the environmental RH increases to more than 68%RH, and its sensitivity increases with the increase of RH, thus it can work as a humidity alarm to protect storage from wetting.
查看更多>>摘要：Space division multiplexing (SDM) techniques based on few-mode or multicore fibers have attracted great interest to enhance the capacity of optical networks, for which laser direct writing (LDW) is a promising approach to realize compact spatial multiplexer/demultiplexer (MUX/DEMUX). However, the modal crosstalk induced by bending multimode waveguide in LDW spatial MUXs/DEMUXs may have significant influence on the overall performance of a weakly-coupled SDM system supporting independent spatial channels. In this paper, we firstly analyze the bend-induced mode coupling behaviors for linearly-polarized (LP) modes in circularly-symmetric-step-index weakly-guiding bending multimode waveguides (WGBMW) and show that LP01 and LP11 modes will have the strongest mode coupling. Then we propose an optimal design of 90-bend and S-bend using hybrid Euler-Circular (HEC) bend, where the length of Euler bend is optimized to be the beat length of LP(01 )and LP(11 )modes to suppress their mode coupling. Numerical simulations based on conformal mapping model and three-dimensional Beam Propagation Method are performed. The simulation results show that the optimal HEC bend can significantly suppress the mode crosstalk and loss. The crosstalk of LP01 and LP11 modes for the optimal HEC bend is below -60 dB, whereas the value for the circular bend is about -23 dB. This work provides a better understanding of bend-induced mode coupling in WGBMWs and is beneficial for the practical design of LDW devices.
查看更多>>摘要：Due to the anisotropic spatial polarization state and spiral phase distribution, the orbital angular momentum (OAM) of vector vortex beams (VVBs) has attracted increasingly attention in recent years. In this paper, the Hybrid-order Poincare sphere VVBs are constructed by orthogonal left-handed (L-H) and right-handed (R-H) circularly polarized vortexes. The vector vortex light fields of different orders at the focal plane are collected and analyzed experimentally. Based on the vector diffraction integral theory, the effects of the topological charge and polarization order for VVBs, as well as the initial phase difference for L-H and R-H components on the OAM properties of focused field for the longitudinal component are investigated numerically. It is found that the OAM density distribution of the longitudinal component shows inner and outer two layers on the whole, and the layers mainly concentrate the corresponding L-H and R-H components respectively. Meanwhile, the signs of the topological charges for L-H and R-H components determine the positive and negative distributions of the inner and outer OAM density respectively. When the initial phase difference of L-H and R-H components 00 changes in the range of 0-2x, the OAM density rotates the angle 00/2 along the clockwise. However, the OAM of the longitudinal component does not change with 00, and increases as the polarization order m increases when the topological charge of VVBs I > 2. The results could be helpful to further explore the applications of the OAM for VVBs in the fields of optical detection and communication.
查看更多>>摘要：We investigate the magnetic dipole spontaneous emission in the periodic all-dielectric subwavelength spheres array by the magnetic dyadic Green function, together with Cartesian multipole decomposition approach. We find that magnetic Purcell factor exhibits energies splitting (forming quasi-normal modes) due to strong coupling effect between different part of all-dielectric optical antennas. The period plays an important role in the magnetic Purcell effect, and there is an optimized period for the optical antenna to maximize the magnetic Purcell factor. In addition, the magnetic dipole along the spheres' dimer axis will significantly couple to the higher order multipolar Mie resonances with magnetic Purcell factor greater than 400. Our work will help to design all-dielectric nanoantennas to manipulate magnetic light emission originating from magnetic-dipole transitions and study the magnetic light-matter interactions in topological photonics.
Sagor, Rakibul HasanTathfif, InfiterHassan, Md. FarhadRashid, Kazi Sharmeen...
12页
查看更多>>摘要：A refractive index nanosensor with Metal-Insulator-Metal (MIM) waveguide setup, incorporating a concentric triple ring resonator (CTRR), is presented in this article. The proposed sensor identifies unknown materials by exploiting the linear interrelation between the refractive index and the corresponding shift of the resonant wavelength, aided by the Finite Element Method (FEM). Optimization of the initial structural parameters is performed one by one to increase the sensitivity of the designed sensor to the utmost. As a result, a maximum sensitivity of 3639.79 nm/RIU is obtained for gas sensing, with a FOM (Figure of Merit), FOM*, and Q-factor of 91.02, 0.26 x 10(6), and 99.75, respectively. Furthermore, the proposed optimized CTRR sensor displays a maximum sensitivity of 7530.49 nm/RIU for the biologically and chemically important refractive index range 1.30 to 1.40 and can also function as a plasmonic filter. Therefore, the numerous possible applications make the proposed sensor a promising contender in the field of refractive index sensing.
查看更多>>摘要：Coronagraphy is an efficient technique for identifying and characterizing extra-solar planets orbiting in the habitable zone of their parent star. An important family of coronagraphs is based on amplitude or phase filters placed at an intermediate image plane of the optical system, spreading starlight outside of the so-called "Lyot stop"located at the exit pupil plane of the instrument. This article explores the potential of circular amplitude and phase gratings employed as image plane coronagraph filters. It presents a theoretical analysis of the simplest case of an amplitude circular grating and introduces an inversion paradigm with respect to classical Lyot coronagraph, by exchanging its image and pupil masks. Various types of circular gratings are considered and their performance is evaluated with the help of numerical simulations. The most promising solutions are presented and discussed. The main conclusion is that high attenuation ratios of the parent star are feasible, provided that the system is properly optimized with a Lyot stop especially tailored to the grating filter.
NSTL
Elsevier