XUE LinlinBras Samuel Malumba TimoteoQIU WeiweiWANG Zhongpeng...
577-582页
查看更多>>摘要：An ultra-broadband optical filter was proposed and demonstrated based on leaky mode coupling in a coated chirped long-period fiber grating(CLPFG).The CLPFG was coated with a material whose refractive index(RI)was higher than that of the fiber cladding,enabling the coupling of the core mode to leaky modes,to achieve a desired coupling efficiency.Complex coupled-mode theory was used to investigate the power evolution of the core mode that resulted from the coupling.From this,the conditions in which the core mode power attenuates the most rapidly were identified.In addition,phase matching turning point(PMTP)was used in the design,to overcome the conflict between the range of grating period change and the grating length in the CLPFG.Finally,an optimized CLPFG-based filter with a length of 3.5 cm was obtained,which has a symmetrical attenuation band with an operating bandwidth over 300 nm.Within the operating bandwidth,the flatness is less than 2.5 dB and the transmittance is lower than 0.1％.
查看更多>>摘要：Electro-optic(EO)modulator plays a very critical role in the optical communication systems.Here,we report a stimu-lated thin-film lithium niobate(LN)modulator with a half-wave voltage-length product of 1.8 V·cm,which can suc-cessfully achieve modulation and demodulation of a 1 GHz sinusoidal signal with an amplitude of 5 V in experiment.The optical loss caused by metal electrodes is reduced by optimizing the waveguide structure and depositing silica onto the waveguide,and group-velocity matching and characteristic impedance matching are achieved by optimizing the buffer silica layer and the electrode structure for larger bandwidth,which simultaneously improves the modulation efficiency and bandwidth performance.Our work demonstrated here paves a foundation for integrated photonics.
PANG ChengkaiZHANG QiongqiongZHANG HongqiaoHUANG Haiyan...
588-594页
查看更多>>摘要：A multi-channel laser interferometer(MCLI)is proposed to improve the coordinate measurement accuracy.A 780 nm external cavity laser is locked on the D2 line of 87Rb atom by polarization spectroscopy,and a high frequency stabi-lized laser source is obtained with a linewidth of 385.8 kHz at root mean square(RMS).The interferometers share the stabilized source and individually install on 4 axes of a coordinate measuring system.As a result,the measurement uncertainty is reduced from 1.2 pm to 0.2 pm within the dynamic measurement range of 1.0 m.The MCLI is adept at integrate and flexible installation,which caters to various applications on precision measurement.
查看更多>>摘要：Near infrared-Ⅱ(NIR-Ⅱ,1 000-1 700 nm)imaging with high penetration tissue depth and signal-noise ratio has at-tracted wide interest in biomedicine.As a two-dimensional(2D)material with narrow band gap,the band structure of layered black phosphorus,as an important characteristic of electronic structure,determines the electronic transport and infrared optical properties,which show great potential in NIIR-Ⅱ imaging.Here,the electronic structure and NIR-Ⅱoptical properties of black phosphorus have been investigated in detail by employing the generalized gradient ap-proximation+U(GGA+U)correction based on density functional theory(DFT).First,we performed the band struc-ture and density of states for different layers of black phosphorus.From the electronic structures,the location of va-lence band maximum didn't shift obviously,and the position of conduction band minimum shifted downward gradu-ally,inducing the band gaps decreased gradually with the increasing layer number.While the layer number increased to 5,the behaviour of electronic structure was very similar to that of the bulk black phosphorus.Then,we calculated the NIR-Ⅱ optical properties,and found the optical band gap of black phosphorus also showed layer dependent proper-ties.From a single layer to 5 layers,the optical band gap changed from 1.71 eV to 0.92 eV.It is noting that black phosphorus also showed the significant optical absorption in NIR-Ⅱa(1 300-1 400 nm)and NIR-Ⅱb(1 500-1 700 nm)windows.Especially,the NIR-Ⅱ optical absorption can be enhanced with increasing the layer number to 5,indicating promising photoresponse materials in NIR-Ⅱ imaging.
查看更多>>摘要：We theoretically investigate the evolution of dark screening spatial solitons originating from the quadratic electro-optic effect in biased centrosymmetric photorefractive(CP)crystal by using beam propagation method(BPM).The results indicate that the multiple dark solitons sequence can be obtained in the CP crystal with the odd or even initial condi-tions.If the initial width of the dark notch is smaller,only a fundamental soliton or a Y-junction soliton pair is gener-ated.When the initial width of the dark notch and the bias electric field are increased,the multiple dark spatial solitons sequence is formed,which realized a progressive transition from a low-order soliton to a higher-order solitons se-quence in both odd and even conditions.The solitons characteristic is similar to that of screening solitons in the non-centrosymmetric photorefractive(NCP)crystals.
查看更多>>摘要：In this work,the symbol error rate(SER)performance of a relay-assisted underwater wireless optical communication(UWOC)system has been investigated over the composite exponential-generalized gamma(EGG)distribution with the beam spread function(BSF)under two hard decision schemes of fixed decision threshold(FDT)and dynamic de-cision threshold(DDT).Specifically,the oceanic turbulence is assumed to follow the EGG distribution,and the im-pacts of absorption,scattering and misalignment loss are characterized by BSF.The cumulative distribution function(CDF)of this UWOC system is derived with the max-min criterion as the best path selection scheme.And with the help of Gauss-Laguerre quadrature function,the analytical SER expressions for these two threshold schemes are then achieved and validated by Monte Carlo(MC)simulation.Moreover,the SER performance is further studied under dif-ferent temperature gradients,bubble levels(BLs)and water salinity over three water types,as well as the system structure parameters.Results show that the UWOC system with DDT scheme can efficiently overcome the error floor induced by FDT scheme and demonstrates better SER performance.Furthermore,the SER performance would be im-proved with lower BL,temperature gradients and water salinity as well as the concentration of dissolved particles.This work will benefit the design and research of relay-assisted UWOC system.
查看更多>>摘要：For particle image velocimetry(PIV)technique,the two-dimensional(2D)PIV by one camera can only obtain 2D ve-locity field,while three-dimensional(3D)PIV based on tomography by three or four cameras is always complex and expensive.In this work,a binocular-PIV technology based on two cameras was proposed to reconstruct the 3D velocity field of gas-liquid two-phase flow,which is a combination of the binocular stereo vision and cross-correlation based on fast Fourier transform(CC-FFT).The depth of particle was calculated by binocular stereo vision on space scale,and the plane displacement of particles was acquired by CC-FFT on time scale.Experimental results have proved the effec-tiveness of the proposed method in 3D reconstruction of velocity field for gas-liquid two-phase flow.
查看更多>>摘要：Aiming at the noise disturbance of unwrapping phases of control points in the camera-projector calibration system,a random sample consensus(RANSAC)based plane fitting method is proposed to filter the phase noise in this paper.Different from the classical least squares method using all data,the points with noise will not be used to fit the plane in the proposed RANSAC method,which improves the accuracy of plane fitting.The proposed method suits for any two-dimensional(2D)calibration patterns,such as checkerboard or black dots with white background,which improves the flexibility of camera-projector system calibration.
查看更多>>摘要：Surface electromyography(EMG)is a bioelectrical signal that recognizes speech contents in a non-acoustic form.Ac-tivity detection is an important research direction in EMG research.However,in the low signal-to-noise ratio(SNR)environment,it is difficult for traditional methods to obtain accurate active signals.This paper proposes a new en-ergy-based spectral subtraction backtracking(E-SSB)method to segment EMG active signal in the low SNR environ-ment.Compared with traditional energy detection,the algorithm in this paper adds spectral subtraction(SS)to filter out the clutter,and raises a retrospective idea to improve the classification performance.The experiment results show the proposed activity detection method is more effective than other methods in the low SNR environment.
查看更多>>摘要：Recently,the generative adversarial network(GAN)has been extensively applied to the cross-modality conversion of medical images and has shown outstanding performance than other image conversion algorithms.Hence,we propose a novel GAN-based multi-domain registration method named multiscale diffeomorphic jointed network of registration and synthesis(MDJRS-Net).The deviation of the generator of the GAN-based approach affects the alignment phase,so a joint training strategy is introduced to improve the performance of the generator,which feedbacks the structural loss contained in the deformation field.Meanwhile,the nature of diffeomorphism can enable the network to generate deformation fields with more anatomical properties.The average dice score(Dice)is improved by 1.95％for the computer tomography venous(CTV)to magnetic resonance imaging(MRI)registration task and by 1.92％for the CTV to computer tomography plain(CTP)task compared with the other methods.
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维普