A V-Folded Digital Laser for On-Demand Vortex Beams by Astigmatic Transformation of Hermite–Gaussian Modes

A V-folded digital laser using a spatial light modulator(SLM)for intra-cavity loss shaping is exploited to generate Hermite-Gaussian modes with on-demand mode order.With aπ/2 astigmatic mode converter,vortex beams carrying on-demand orbital angular momentum(OAM)with a tunable range from-11h to 12 h are obtained.The mode order of the HG mode,hence the OAM of the vortex beam,is digitally switched by changing the phase pattern imposed on the SLM without requiring any mechanic alignment of the cavity.This work has great potential applications in various OAM-tunable vortex beams.

Boosting the Electrochemical Performance of Li-and Mn-Rich Cathodes by a Three-in-One Strategy

There are plenty of issues need to be solved before the practi-cal application of Li-and Mn-rich cathodes,including the detrimental voltage decay and mediocre rate capability,etc.Element doping can e ectively solve the above problems,but cause the loss of capacity.The introduction of appropriate defects can compensate the capacity loss;however,it will lead to structural mismatch and stress accumulation.Herein,a three-in-one method that combines cation–polyanion co-doping,defect construction,and stress engineering is pro-posed.The co-doped Na^(+)/SO_(4)^(2-)can stabilize the layer framework and enhance the capacity and voltage stability.The induced defects would activate more reac-tion sites and promote the electrochemical performance.Meanwhile,the unique alternately distributed defect bands and crystal bands structure can alleviate the stress accumulation caused by changes of cell parameters upon cycling.Consequently,the modified sample retains a capacity of 273 mAh g^(-1)with a high-capacity retention of 94.1%after 100 cycles at 0.2 C,and 152 mAh g^(-1)after 1000 cycles at 2 C,the corresponding voltage attenuation is less than 0.907 mV per cycle.

Experimental Measurement of the Generalized Stokes Parameters of a Radially Polarized Random Electromagnetic Beam

Utilizing the Young’s double slits and Mach-Zehnder interferometer, we proposed an experimental method to measure the generalized Stokes parameters of a radially polarized random electromagnetic beam. After the partially coherent beam propagating through the Young’s double slits, the interference fringe is obtained by the help of a Mach-Zehnder interferometer consisting of apertures, quarter-wave plates and polarizers. The electric cross-spectral density matrix is detected by the coherence degree of interference fringe and the density of each single slit. The generalized Stokes parameters can be obtained from the electric cross-spectral density matrix. This experiment measures the generalized Stokes parameters of the random electromagnetic beam successfully. The results show that the spectral degree of coherence for copolarized cases (xx and yy) is similar with that for cross-polaried cases (xy and yx) for the radially polarized random electromagnetic beam. This method will help us determine the change of the polarization and coherence of the light in propagation by detecting the change of the generalized Stokes parameters.

Light Focusing through Scattering Media by Particle Swarm Optimization

We demonstrate light focusing through scattering media by introducing particle swarm optimization for modulat- ing the phase wavefront. Light refocusing is simulated numerically based on the angular spectrum method and the circular Gaussian distribution model of the scattering media. Experimentally, a spatial light modulator is used to control the phase of incident light, so as to make the scattered light converge to a focus. The influence of divided segments of input light and the effect of the number of iterations on light intensity enhancement are investigated. Simulation results are found to be in good agreement with the theoretical analysis for light refocusing.

Propagation characteristics of a high-power broadband laser beam passing through a nonlinear optical medium with defects

The intensity distributions of a high-power broadband laser beam passing through a nonlinear optical medium with defects and then propagating in free space are investigated based on the general nonlinear Schr¨odinger equation and the split-step Fourier numerical method. The influences of the bandwidth of the laser beam, the thickness of the medium,and the defects on the light intensity distribution are revealed. We find that the nonlinear optical effect can be suppressed and that the uniformity of the beam can be improved for a high-power broadband laser beam with appropriate wide bandwidth. It is also found that, under the same incident light intensity, a thicker medium will lead to a stronger self-focusing intensity, and that the influence of defects in the optical elements on the intensity is stronger for a narrowband beam than for a broadband beam.

Stimulated Brillouin scattering phase conjugation of light beams carrying orbit angular momentum(Invited Paper)

We investigate the stimulated Brillouin scattering （SBS） properties of light beams carrying orbit angular momentum （OAM）. The phase conjugation of light beams carrying OAM is experimentally achieved in an SBS mirror with a random phase plate. The spectrum and the pulse width compression of SBS light are measured. It is shown that the phenomena of pulse compression is observed and OAM conservation is confirmed in the SBS process. The OAM transfer from photons to phonons may find potential applications in photon-phonon conversion-based signal-processing schemes by using OAM multiplexing.

Depolarization field in relaxor-based ferroelectric single crystals under one-cycle bipolar pulse drive

The [001]c-polarized(1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3(PMN-PT) single crystals are widely used in ultrasonic detection transducers and underwater acoustic sensors. However, the relatively small coercive field( 2 kV/cm) of such crystals restricts their application at high frequencies because the driving field will exceed the coercive field. The depolarization field can be considerably larger in an antiparallel direction than in a parallel direction with respect to polarization when the bipolar driving cycle starts. Thus, if the direction of the sine wave signal in the first half cycle is opposite to the polarization direction, then the depolarized domains can be repolarized in the second half of the sine cycle. However, if the direction of the sine wave signal in the first half of the cycle is along the polarization direction, then the change is negligible,and the domains switched in the second half of the sine cycle cannot be recovered. The design of electric driving method needs to allow the use of a large applied field to emit strong enough signals and produce good images. This phenomenon combined with the coercive field increases with the driving frequency, thereby making the PMN-PT single crystals usable for high-frequency applications. As such, the applied field can be considerably larger than the conventionally defined coercive field.

Towards integrated mode-division demultiplexing spectrometer by deep learning

Miniaturized spectrometers have been widely researched in recent years,but few studies are conducted with on-chip multimode schemes for mode-division multiplexing(MDM)systems.Here we propose an ultracompact mode-division demultiplexing spectrometer that includes branched waveguide structures and graphene-based photodetectors,which realizes simultaneously spectral dispersing and light fields detecting.In the bandwidth of 1500-1600 nm,the designed spectrometer achieves the single-mode spectral resolution of 7 nm for each mode of TE_(1)-TE_(4) by Tikhonov regularization optimization.Empowered by deep learning algorithms,the 15-nm resolution of parallel reconstruction for TE_(1)-TE_(4) is achieved by a single-shot measurement.Moreover,by stacking the multimode response in TE_(1)-TE_(4) to the single spectra,the 3-nm spectral resolution is realized.This design reveals an effective solution for on-chip MDM spectroscopy,and may find applications in multimode sensing,interconnecting and processing.

Output Prediction of Helical Microfiber Temperature Sensors in Cycling Measurement by Deep Learning

The inconsistent response curve of delicate micro/nanofiber(MNF)sensors during cycling measurement is one of the main factors which greatly limit their practical application.In this paper,we proposed a temperature sensor based on the copper rod-supported helical microfiber(HMF).The HMF sensors exhibited different light intensity-temperature response relationships in single-cycle measurements.Two neural networks,the deep belief network(DBN)and the backpropagation neural network(BPNN),were employed respectively to predict the temperature of the HMF sensor in different sensing processes.The input variables of the network were the sensor geometric parameters(the microfiber diameter,wrapped length,coiled turns,and helical angle)and the output optical intensity under different working processes.The root mean square error(RMSE)and Pearson correlation coefficient(R)were used to evaluate the predictive ability of the networks.The DBN with two restricted Boltzmann machines(RBMs)provided the best temperature prediction results(RMSE and R of the heating process are 0.9705℃and 0.9969,while the values of RMSE and R of the cooling process are 0.7866℃and 0.9977,respectively).The prediction results obtained by the optimal BPNN(five hidden layers,10 neurons in each layer,RMSE=1.1266℃,R=0.9957)were slightly inferior to those obtained by the DBN.The neural network could accurately and reliably predict the response of the HMF sensor in cycling operation,which provided the possibility for the flexible application of the complex MNF sensor in a wide sensing range.

Dynamical approach to quantum optomechanics:Motivation,method,and applications

We present an overall summary on a method to deal with quantum dynamics of optomechanical systems.The method is based on the dynamical evolution processes instead of the finally evolved steady states,which are a prerequisite to the standard approach,and well captures the features in optomechanical cooling,entanglement and other scenarios.

Facile fabrication of core-shell Ni3Se2/Ni nanofoams composites for lithium ion battery anodes

Due to the highly porous structure,large specific surface area,and 3 D interconnected metal conductive network,nanoporous metal foams have attracted a lot of attention in the field of energy conversion and storage,especially lithium-ion batteries,which are ideal for current collectors.In this work,we develop a facile approach to fabricate core-shell Ni3Se2/Ni nanofoams composites.The Ni3Se2/Ni composites make full use of both the advantages of metal conductive network and core-shell structure,resulting in a high capacity and superior rate performance.In addition,the composites can be directly converted into electrode by a simple mechanical compression,which is more convenient than traditional casting method.What’s more,this material and its structure can be extended to other devices in the field of energy conversion and storage.

Bilayer carbon-based structure with the promotion of homogenous nucleation for lithium metal anodes

Lithium metal anodes (LMAs) are considered as the promising alternatives for next-generation high energy density batteries,but are still hampered by the severe growth of uncontrollable lithium dendrites.The growth of lithium dendrites induces poor cycling lifespan and serious safety concerns,dragging lithium metal batteries out of practical applications.We designed a bilayer carbonbased structure covered with Co/C nanosheets and vertical graphene sheets (VGS).The enormous specific surface area and uniformly distributed Co nanoparticles of the CC@Co/C-VGS host are derived from its unique design,which can reduce local current density and nucleation overpotential,resulting in a dendrite-free morphology and exceptional cycling stability.Symmetric cells exhibit over 400 cycles (800 h) at a high current density/capacity of 10 mA cm^(-2)/10 mA h cm^(-2).Full cells using LiFePO_(4)as the cathode have an enhanced rate capability and a prolonged lifespan,reaching 90 mA h g^(-1)after 1000 cycles at 2 C with 73.5% capacity retention.This unique design sheds light on developing high-performance LMAs.

Estimating topological charge of propagating vortex from single-shot non-imaged speckle

Encoding information using the topological charge of vortex beams has been proposed for optical communications. The conservation of the topological charge on propagation and the detection of the topological charge by a receiver are significant in these applications and have been well established in free-space. However, when vortex beams enter a diffuser,the wavefront is distorted, leading to a challenge in the conservation and detection of the topological charge. Here, we present a technique to measure the value of the topological charge of a vortex beam obscured in the randomly scattered light. The results of the numerical simulations and experiments are presented and are in good agreement. In particular, only a single-shot measurement is required to detect the topological charge of vortex beams, indicating that the method is applicable to a dynamic diffuser.

Experimental measurement of scintillation index of vortex beams propagating in turbulent atmosphere

The scintillation indices(SIs)of Gaussian beams and vortex beams propagating in turbulent atmosphere are investigated experimentally.It is shown that with the increase of propagation distance,the SI of Gaussian beam around optical axis increases gradually,but the SI of vortex beam with topological charge of 4 increases,achieves the maximum value at a fixed distance,and then decreases as the continued increase of propagation distance.The SI of vortex beam can be smaller than that of Gaussian beam under certain conditions.

Light focusing through strongly scattering media by binary amplitude modulation

Based on the angular spectrum method and the circular Gaussian distribution(CGD) model of scattering media,we numerically simulate light focusing through strongly scattering media.A high contrast focus in the target area is produced by using feedback optimization algorithm with binary amplitude modulation.It is possible to form the focusing with one focus or multiple foci at arbitrary areas.The influence of the number of square segments of spatial light modulation on the enhancement factor of intensity is discussed.Simulation results are found to be in good agreement with theoretical analysis for light refocusing.

Multiple multicontrol unitary operations: Implementation and applications

The efficient implementation of computational tasks is critical to quantum computations. In quantum circuits, multicontrol unitary operations are important components. Here, we present an extremely efficient and direct approach to multiple multicontrol unitary operations without decomposition to CNOT and single-photon gates. With the proposed approach, the necessary twophoton operations could be reduced from O(n^3) with the traditional decomposition approach to O(n), which will greatly relax the requirements and make large-scale quantum computation feasible. Moreover, we propose the potential application to the(n-k)-uniform hypergraph state.

Recognizing the orbital angular momentum(OAM)of vortex beams from speckle patterns

The orbital angular momentum(OAM)of vortex beams offers a new degree for information encoding,which has been applied to optical communications.OAM measurement is essential for these applications,and has been realized in free space by several methods.However,these methods are inapplicable to estimate the OAM of vortex beams directly from the speckle patterns in the exit end of a multimode fiber(MMF).To tackle this issue,we design a convolutional neural network(CNN)to realize 100%accuracy recognition of two orthogonally polarized OAM modes from speckle patterns.Moreover,we demonstrate that even when the speckle patterns are cropped to only 1/64 of the original patterns,the recognition accuracy of the designed neural network is still higher than 98%.We also study the recognition accuracy of cropped speckles in different areas of speckle patterns to verify the feasibility of OAM recognition after cropping.The results demonstrate that recognizing the OAMs of two orthogonally polarized vortex beams from only a portion of speckle patterns in the exit end of an MMF is feasible,offering the potential to construct a 1×N data transmission scheme.

Compact auto-stereoscopic display based on directional backlight using side-glowing polymer optical fiber array

A compact directional backlight module of time-multiplexed auto-stereoscopic display based on side-glowing polymer optical fiber(SGPOF)is proposed.The optical system is mainly composed of SGPOF array and cylindrical lens array.Spatial crosstalk is reduced by inserting a grating film as multi-slit diaphragm between the SGPOF array and the cylindrical lens array.A theoretical model is constructed based on the imaging optics principle of the off-axis ray.In the experiments,the cylindrical lens array concentrates a small number of views on three different view zones,the display can provide high luminance.The measurement results show that the luminance uniformity of the backlight module is up to 89.6%,and in the viewing zone the crosstalk is lower than 10%.The backlight module is compacted that the thickness being only 7 mm.The full-resolution and low-crosstalk 3D images are realized by using SGPOF backlight.

Correlation Holography with A Single-Pixel Detector:A Review

Correlation holography uses incoherent light to reconstruct holograms.This technique reconstructs objects as distributions of two-point coherence function rather than using optical fields,as in conventional holography.The basic principle of correlation holography is derived from the van Cittert--Zernike theorem and relies on the similarity between the optical field and the coherence functions.Experimental implementation of the correlation holography techniques requires a field or intensity interferometer,and fringe analysis and crosscovariance measurement in these interferometers require a conventional camera with array detectors.With the availability of digitally controlled diffractive elements,it is possible to replace the incoherent light source,such as a rotating ground glass,with a digital source loaded with the random patterns in sequence.Such strategies ease the burden on the detector and allow for correlation holography with a single-pixel detector(SPD)to be used.This review paper discusses a close connection between digital holography and correlation holography.The principles of correlation holography with the SPD are reviewed in detail,and the advantages of using digital sources to mimic incoherent illumination in the correlation holography are examined in the context of three-dimensional and complex field imaging.