Abstract:In order to meet the high-resolution and wide spectrum range of the backscattering Raman system, this paper designs and builds a Raman test system based on the echelle spectrometer. In the optical splitting system, compared with the ordinary planar grating spectrometer, the use of the echelle improves the resolution of the system without increasing the volume of the system. The use of intensified charge-coupled device (ICCD) in the detection system improves the signal-to-noise ratio (SNR) and the detection limit of weak spectrum. Finally, the Raman system was spectrally calibrated. The broadband backscattering Raman experimental results are given and discussed. The experimental results show that the system has an excellent application prospect for broadband and high-resolution Raman spectrum measurement.

Abstract:We proposed a graphene based active plasmonic device by the introduction of graphene-MoS2 heterostructures. The device was composed of a monolayer MoS2 layer between the silicon substrate and periodically arranged graphene nanoribbon arrays. The finite-difference time domain (FDTD) method was used to analyze and compare the changes of the surface plasmon resonant wavelength and modulation depth (MD) in the two cases with and without MoS2. It was found that all the parameters of the width, period and Fermi level of the graphene nanoribbons affect the surface plasmon resonant wavelength of the plasmonic device. The introduction of the monolayer MoS2 can produce a redshift about 3 μm of the surface plasmon resonant wavelength, while the MD is basically unchanged. The redshift of the graphene surface plasmon resonant wavelength will provide application prospects for new active graphene plasmonic devices.

Abstract:The performance of an optical time domain reflectometer (OTDR) is significantly improved using spread spectrum technology. The concept of spread spectrum OTDR (SSOTDR) is proposed, the theoretical basis and simulation results of the new method are given, and the problem of direct application of bipolar spread spectrum codes to OTDR and despreading in the optical domain are solved. The simulation results show the feasibility of the SSOTDR, which exhibits better dynamic range reported to date for a practical long-haul OTDR system without using conventional average technique.

Abstract:The poor film formation of CdSe/ZnS quantum dots (QDs) during spin-coating makes a substantial impact on the device performance of quantum dot light-emitting diodes (QLEDs). This work proposes a method to improve the morphology of the quantum dot light-emitting layer (EML) by adding small organic molecular 4,4'-Bis(9H-carbazol-9-yl) biphenyl (CBP) into the layer. Its surface roughness reduces from 6.21 nm to 2.71 nm, which guarantees a good contact between hole transport layer (HTL) and EML. Consequently, the CdSe/ZnS QDs:CBP based QLED achieves maximum external quantum efficiency (EQE) of 5.86%, and maximum brightness of 10 363 cd/m2. It is demonstrated that the additive of small organic molecules could be an effective way to improve the brightness and the efficiency of QLEDs.

Abstract:The cholesterol solution concentration sensing characteristics based on tilted fiber Bragg grating (TFBG) are investigated by means of theoretical analysis and experiments. We prepare two groups of cholesterol solutions with the same concentration range and different refractive index ranges. The sensitivity of the two groups of solutions was 11.83 pm∙mL/mg and 124.79 pm∙mL/mg, respectively. The results show that the sensitivity of cholesterol solution can be improved by adjusting the refractive index range. This conclusion is valuable for measuring the concentration of fat-soluble solution.

Abstract: In this paper, we present a phase multiplication algorithm (PMA) to obtain scalable fringe precision in laser self-mixing interferometer under a weak feedback regime. Merely by applying the double angle formula on the self-mixing signal multiple times, the continuously improved fringe precision will be obtained. Theoretical analysis shows that the precision of the fringe could be improved to λ/2n+1. The validity of the proposed method is demonstrated by means of simulated SMI signals and confirmed by experiments under different amplitudes. A fringe precision of λ/128 at a sampling rate of 500 kS/s has been achieved after doing 6th the PMA. Finally, an amplitude of 50 nm has been proved to be measurable and the absolute error is 3.07 nm, which is within the theoretical error range. The proposed method for vibration measurement has the advantage of high accuracy and reliable without adding any additional optical elements in the optical path, thus it will play an important role in nanoscale measurement field.

Abstract:In the practical application, a wide-angle absorption with simple structure is still crucial property of metamaterial absorbers (MAs). A single-band infrared MA is introduced to analyze the angle insensitive mechanism. Numerical simulation reveals that a perfect absorption peak with 99.9% (7.55 μm) is achieved at normal incidence, as well as the absorptivity is respectively 69.7% (7.46 μm) and 93.5% (7.46 μm) for transverse electric (TE) and transverse magnetic (TM) modes at 70° incidence. By changing substrate thickness, the absorption ratio at 70° is increased to 91% (7.46 μm) for TE mode. Our design can also keep the good absorption stability for the geometric parameters. The Ez-field distributions for different incident angles are given to investigate the physical mechanism. The designed MA can realize good wide-angle tolerance. This MA owns great applications, including infrared spectroscopy, solar harvester and plasmonic sensors.

Abstract:Theoretical analysis and experimental study on the thickness distribution of Ta2O5 film evaporated on the inner-face of a hemispherical substrate are demonstrated. It is derived that the value of n/R and L/R influence the film thickness distribution (where R is the radius of the hemisphere, n and L are the horizontal distance and vertical height between the evaporation source and the center of the hemisphere, respectively). The whole hemispherical substrate can be coated when n≤L+R, otherwise there is a “blind area” on the substrate when the substrate is self-rotating. A hemispherical composite substrate with a radius of 200 mm is coated with Ta2O5 protective film under a certain configuration, the thickness of Ta2O5 film at the edge is 0.372 times the film at the vertex which shows that the evaporation characteristics of Ta2O5 tend to be a point source.

Abstract:In this paper, an asymmetric array structure of space laser communication receiver is proposed. This structure can greatly reduce alignment requirement, and lighten the signal strength jitter caused by atmospheric turbulence. A prototype of the proposed structure is fabricated and a 2.5 Mbit/s on-off keying (OOK) modulated demonstration link over 40 m free space is built. This asymmetric array structure can effectively collect optical signal while rotating in a window angle of ±17°, and the bit error ratio (BER) keeps zero.

Abstract:In order to improve the spectrum efficiency of the high-order polar coded modulation systems, the polar code is used as the component code of the bit-interleave coded modulation (BICM) system, a novel bit mapping scheme is proposed considering of the channel polarization and successive cancellation (SC) decoding principle of polar codes as well as the unequal protection of equivalent channels by modulator. In this scheme, the frozen bits on the unreliable split channel are allocated to the equivalent channel with the low protection of the modulator, while the equivalent channels with the high protection are used to transmit the information bits. Thus, the error-correcting performance of polar codes is improved. Compared with some bit mapping schemes, the proposed bit mapping scheme only needs to divide and choose the parameters of the split channels reliability measurement, the complexity does not increase obviously, and simulation results show that the proposed scheme has the better performance under the quadrature amplitude modulation (QAM) modulation based on the Gray mapping.

Abstract:We propose a video image mosaic method based on multi-module cooperation. This method stitches the video into a panorama with a large field of view, divided into three modules:the key frame selection module, the image mosaic module, and the optimization module. The key frame selection module obtains key frames by comprehensively evaluating the overlap rate and image quality. The image mosaic module stitches the key frames into a panoramic image to generate an initial mosaic result. The optimization module makes the mosaic result more natural and eliminates ghosts by using object detection advantages. Our method is tested on videos taken in real scenes, and the results have a more comprehensive and natural description.

Abstract:Simultaneous localization and mapping (SLAM) technology is a research hotspot in the field of intelligent mobile robot, and many researchers have developed many classic systems in the past few decades. However, most of the existing SLAM methods assume that the environment of the robot is static, which results in the performance of the system being greatly reduced in the dynamic environment. To solve this problem, a new dynamic object detection method based on point cloud motion analysis is proposed and incorporated into ORB-SLAM2. First, the method is regarded as a preprocessing stage, detecting moving objects in the scene, and then removing the moving objects to enhance the performance of the SLAM system. Experiments performed on a public RGB-D dataset show that the motion cancellation method proposed in this paper can effectively improve the performance of ORB-SLAM2 in a highly dynamic environment.

Abstract:In this letter, we present a novel integrated feature that incorporates traditional parameters, and adopt a parallel cascading fashion network HazeNet for enhancing image quality. Our unified feature is a complete integration, and its role is to directly describe the effects of haze. In HazeNet, we design two separate structures including backbone and auxiliary networks to extract feature map. Backbone network is responsible for extracting high-level feature map, and low-level feature learned by the auxiliary network can be interpreted as fine-grained feature. After cascading two features with different accuracy, final performance can be effectively improved. Extensive experimental results on both synthetic datasets and real-world images prove the superiority of the proposed method, and demonstrate more favorable performance compared with the existing state-of-art methods.