查看更多>>摘要：In order to study the transmission characteristics of polarized light in the atmosphere under the influence of multiple factors, the polarization Monte Carlo model is established based on Mie scattering theory and Stokes vector, and the scattering depolarization of photons in the atmosphere is calculated and analyzed. The effects of four typical aerosol particles with different optical depth on the forward scattering of 1064 nm narrow-pulse laser with different polarization states are systematically analyzed. The results show that with the increase of optical depth, the degree of polarization of several polarized light decreases to varying degrees. Among them, circularly polarized light has better polarization retention than linearly polarized light, and dust particles have the most significant depolarization characteristics than water soluble particles, sea salt particles and soot particles. Through the calculation and analysis of the variation of Stokes parameters of forward scattering light with the increase of optical depth, it is found that the polarization angle of circularly polarized light scattered by medium is not easy to change than that of linearly polarized light. At the same time, the model results also show that the scattering medium with larger particle size has more significant depolarization characteristics, and the circularly polarized light is insensitive to the change of particle size in the scattering process. The research results of this paper can provide reference for the application of narrow-pulse polarization laser in laser remote sensing, laser guidance, laser communication and laser radar, and provide data basis and theoretical guidance for the development of narrow-pulse polarization laser equipment.
查看更多>>摘要：A novel high-sensitive temperature sensor with parallel polydimethylsiloxane (PDMS)-filled Fabry-Perot interferometers (FPIs) based on dual Vernier effect was proposed and demonstrated. The sensor is composed of two parallel FPIs with similar free spectrum range fabricated by splicing a section of silica tube to single-mode fiber. One is partially filled with PDMS to form an air cavity, and the other is fully filled with PDMS to form a PDMS cavity. Owing to the difference structures of two FPIs and the excellent characteristics of PDMS, the reflective spectra of two FPIs shift to opposite directions with the changes of ambient temperature. Two FPIs serve as reference FPI for each other in temperature measurement, resulting in the dual Vernier effect to enhance Vernier effect. The experimental results show that the proposed sensor exhibits a high temperature sensitivity of 7.61 nm/degrees C with good linearity. This work provides a new strategy for the fiber-optic sensing field.
查看更多>>摘要：The modulation of degree of spatial coherence (DOSC) plays an optical gating which highly correlates with the coherence volume (CV) in the proposed DOSC laser scanning confocal fluorescence microscope (DOSC-LSCFM). The axial resolution at sub-diffraction-limit performance was demonstrated and discussed.
查看更多>>摘要：Micro/nanofibres have been emerging as an interdisciplinary platform for exploring novel sensing technology on the micro/nanoscale. This work proposes and demonstrates an ultrasensitive and stable pressure sensor based on the perturbation of adiabatic conditions during the optical mode evolving in the transition region. In our experiment, when attached to a glass slide, the sensor shows ultrahigh pressure sensitivity of 1.52 kPa-1 which is about three times the sensitivity of the waist region. Simultaneously, the sensing region of the fibre has a diameter of tens of microns to provide a better mechanical structure strength. These preliminary results demonstrate that the sensor has the advantages of stable structure, high sensitivity, and simple preparation process, which may have potential in practical applications.
Nie, LongzhiKong, LingranDong, NenghaoJiang, Kaijun...
7页
查看更多>>摘要：We experimentally and theoretically characterize the temporal rotation and radial twist of the interference pattern of a vortex beam with its conjugate copy. To quantitatively study the temporal rotation and radial twist, we controllably modify the conjugate beam to obtain a frequency or wavefront curvature difference using a movable Mach-Zehnder interferometer. The effects of the physical parameters (i.e., the topological charge, frequency difference and wavefront curvature difference of the vortex beams) on the temporal rotation as well as radial twist are systematically explored. We further measure two parameters, the rotation velocity SL and twist coefficient a, respectively, to characterize the degree of the temporal rotation and radial twist of the interference pattern. The theory of the interference model on vortex beams has good agreement with the experimental results. This work is helpful for study on the detailed structure of the interference pattern and manipulation of matter with superimposed vortex beams.
查看更多>>摘要：To suppress the dark current and improve the detection sensitivity of the Germanium-on-silicon (Ge-on-Si) avalanche photodiode (APD), we report an integrated waveguide-based Ge-on-Si APD with a lateral separate absorption charge multiplication (SACM) structure, which works at low bias voltage. The breakdown voltage (V-br) of the lateral SACM APD in linear mode is about 5.81 V, and the device demonstrates very low dark current of 0.157 nA and 40.7 nA at unity gain voltage (V-Gain=1 = 3.5 V) and 0.95V(br) (~5.5 V), at room temperature. We also study the single photon detection performance of the device in Geiger mode. The practical dark count rate (DCR) at 300 K is with the same order of magnitude as the vertical SACM Ge-on-Si APD operating at 200 K. With the wavelength and average photon number of weak coherent pulse are 1550 nm and 0.1, respectively, the theoretical single photon detection efficiency (SPDE) of the device can achieve 0.4% at 300 K, which will reduce the dependence of the weak light detection system on the low-temperature working environment.
查看更多>>摘要：This paper proposes the design of a silicon photonic crystal waveguide with a hexagonal lattice structure. In the proposed structure, the effect of temperature variation on the photonic band edges has been studied. Structural design parameters have been optimized for TM and TE modes to obtain bandgap in the optical communication window of 1550 nm at room temperature. The variation in the refractive index of the silicon slab with temperature ranging from 300 K-400 K has been considered and the tuning of photonic band-edge wavelength with thermo-optic effect is presented. The band edges are found to shift linearly with changes in temperature for both TE and TM modes. A sensitivity of 0.0595 nm/K for TM mode and 0.0587 nm/K for TE mode has been observed and thus the proposed structure can be used as a temperature sensor. This paper also presents the tuning of the bandgap and band-edges by changing the refractive index of the holes in the proposed structure. The wavelength of the band-edges is found to increase whereas the bandgap is found to decrease on increasing the refractive index of the holes for both TM and TE modes. It is observed that the proposed structure offers a refractive index sensitivity of 10.105 nm/RIU for TM mode and 34.953 nm/RIU for TE mode and thus can be used as a refractive index sensor.
查看更多>>摘要：Synthetic fractals have a large potential to achieve tunability and broadband serviceability for multimodal microwave devices owing to their scale-invariant property that generate strongly enhanced local fields with multiscale spatial distributions over multi-spectral ranges. Herein, we demonstrate a microwave metasurface absorber consist of periodic supercells of Fibonacci spiral capable of achieving highly efficient absorptions in a certain bandwidth and several discrete frequencies. Multiple absorption modes are achieved through the synergistic effect of multiple LC-resonances and cross-coupling of the patterned elements, and a broadband operation is completed by adjusting the thickness of dielectric layer based on interface interference theory. Experimental microwave average absorptivity over 82.9% (reflection loss, RL <= -7 dB) covering the 10.82-14.18 GHz region is obtained and the maximum absorptivity exceeds 99.8% with sub-wavelength thickness (0.039 lambda(0)). These results demonstrate that the synthetic fractal metasurface can be a good candidate absorber for microwave applications like sensing, multiband detecting and filtering.
查看更多>>摘要：In this letter, we have experimentally observed the spatiotemporal mode-locking (STML) in an all-fiber multimode laser with different chromatic dispersions at 1.5 mu m. In the anomalous dispersion regime, not only the stable multimode conventional solitons (CSs), but also the loosely bound solitons (BSs) are achieved, with specific set of polarization controller (PC) and the state of multimode fiber (MMF) segment. Similarly, in the normal dispersion regime, the oscillator generates the MM dissipative solitons (DSs) or the BSs. Moreover, the operation wavelength of these two types of solitons in normal dispersion regime can be converted between ~1530 nm and ~1550 nm due to the birefringence filter effect. The evolution of the beam profiles is investigated, and we found that the state of the MMF plays a key role in energy distribution of the MM solitons. We believe that our results contribute to the further understanding and exploring of nonlinear characteristics in the STML fiber laser systems.
查看更多>>摘要：Differential absorption LIDAR (DIAL) is an effective way to remotely detect air pollutants and hazardous chemicals in the atmosphere. Based on the traditional dual-wavelength DIAL theory and previous studies, simultaneous measurement of multiple pollutant gases in the atmosphere using a multi-wavelength differential absorption LIDAR (MW-DIAL) is reported. It can measure a variety of harmful chemicals in the environment and improve the precision of the technology. A prototype was demonstrated using a tunable Transversely Excited Atmospheric (TEA) CO2 laser working in the 9-11 mu m band. The prototype could accurately detect NH3, CH3OH, and O-3 simultaneously in a detection and measurement, with correlation coefficients of 0.967, 0.981, and 0.949, respectively. Simulations and the evaluation experiment proved the feasibility of the MW DIAL detection method for multiple pollutant gases in the atmosphere. The field test showed that the MW-DIAL can be utilized to identify and detect the target gas at a 5-km-distance.
NSTL
Elsevier