查看更多>>摘要：Due to the uncertainty that may occur during one experiment, the repetition of the same sample experiment is particularly important. Here we propose a novel eccentric-rotation-scanned ptychography (eRSP), eccentric rotation scanning is used to collect diffraction patterns instead of traditional mesh scanning. In the process of collecting diffraction patterns, only the single variable of rotation angle needs to be controlled. The position error is reduced from two-dimensional to one-dimensional, and the difficulty of experimental operation is greatly reduced. The repeatability of the experiment has been significantly improved. Rotating scanning can also avoid the raster grid pathology. In this paper, the theory of eRSP is introduced, and the feasibility of this method has been analyzed by simulation and optical experiment. A multi-spectral information hiding system based on eRSP was proposed. The double random-phase encoding system with a color random phase mask is embedded into a retractable cylinder. A super-continuum white laser source is used as the incident beam, records the ciphertext diffraction pattern by rotating the cylinder and embedded them into the host image. Additional eccentric distance key, rotation angle key, spectrum key and telescopic distance key are introduced, which greatly enhance the system security. Numerical simulations are implemented to demonstrate the feasibility, security and robustness of the proposed scheme.
查看更多>>摘要：As for the 3D imaging of seabed topography, seabed sunken ships and large underwater buildings, the field of view is a significant technical index of the 3D imaging system. In this paper, a binocular vision imaging system based on fisheye lens is applied to satisfy the requirements for 3D imaging of large underwater scenes. Considering the severe image distortion caused by the large wide-angle of fisheye lens and the failure of pinhole imaging model underwater, the imaging process of underwater fisheye camera is re-described through the parametric representation of four-dimensional light field, and the multi-layer refraction imaging model of underwater binocular stereo vision is established based on fisheye camera. A conversion imaging model is constructed to convert the corrected underwater fisheye image into the equivalent image taken in the air. Combined with the existing stereo matching methods, the converted images realize the 3D reconstruction of a large-scale underwater scene. Experimental results show that the corrected underwater fisheye images have a small average reprojection error, which evidences the effectiveness of the proposed calibration method. In the experiment of 3D reconstruction for the large scene composed of multiple underwater ceramic discs, the reconstructed targets have good 3D imaging shapes, which indicates the developed underwater binocular fisheye camera imaging system has the ability to perform 3D imaging and make observations of large underwater scenes.
查看更多>>摘要：Polarisation-spatial entanglement in coherent reflected paraxial vector light fields across an infinite dielectric interface, for polarised incidence, is studied. Closed form expressions for the polarisation-spatial entanglement is obtained explicitly in the case of Hermite Gaussian and Laguerre Gaussian modes up to first order approximation, assuming arbitrary state of incident polarisation, angle of incidence, waist width, and mode indices. General observations regarding the polarisation-spatial entanglement which hold true irrespective of the aforementioned parameters are arrived at. It is observed that close to 1 ebit of polarisation-spatial entanglement can be obtained for angles near Brewster's incidence. The feasibility of possible experimental measurement of the entanglement obtained in reflected light fields is discussed through the Laguerre Gaussian mode as an example.
查看更多>>摘要：Surface plasmon polariton excitation was demonstrated by fluorescent light from organic para-hexaphenylene (p-6P) nanofibers grown directly on a silver thin film surface. We show results of both photoluminescence lifetime measurements and angle-resolved leakage radiation spectroscopy in the excitation range 420-620 nm, which corresponds to the material photoluminescence band. The optical characteristics of randomly oriented p-6P nanofibers assembled directly on the metal surface are remarkably comparable to those of fibers grown on crystalline substrate surfaces. In addition, compared to mica-transferred fibers, the photoluminescence lifetime is longer. More importantly, they show polarization-insensitive plasmonic activity and are entirely consistent with theoretical predictions. Both analytical and numerical finite-difference time-domain simulations support the experimental data. Our findings open a new avenue for incorporating organic nanofibers into optoelectronic applications by directly depositing the p-6P material onto selected substrates. This direct deposition significantly reduces the deformation of the fiber structure and the impurity introduction, usually implied by the transfer process.
查看更多>>摘要：An optimization method based on the mathematical theory of quadratic Bezier curves is proposed for the design of a free-form trough (FF) reflector in a solar concentrator system. Notably, the continuity (or discontinuity) of the surface generated by the proposed method is almost completely independent of the source-target mapping function. It is shown that the proposed method requires only a small number of structural points to approach the optimal design solution. The ZEMAX simulation results show that, compared with traditional cylindrical and parabolic trough concentrators, the FF concentrator yields an effective improvement in the irradiance uniformity on the heat pipe surface. Notably, the proposed method adopts a purely algebraic approach and is hence easily implemented in computer code.
查看更多>>摘要：The resonant high-order harmonic generation (HHG) from solid in the periodic potential is investigated by a chirped laser pulse. We show the dependence of the intensity of the resonance peak on the chirp parameters beta, and it is found that the increase of the resonant harmonic intensity with beta is significantly higher than that of the nonresonance ones. The frequency of the resonance peaks remains at 4.2 eV, which equals to the band gap energy between the valance band (VB) and the conduction band (CB1). By adjusting the chirp parameters, the electron will be injected into the conduction band which results in the band gap emission. Through the time-dependent population imaging (TDPI) and the time-frequency (TF) investigation, we demonstrate that the resonance peak originates from the transition of electrons from the VB toward CB1.
查看更多>>摘要：This note aims to report and correct a mistake in the mentioned paper by Sharifzadeh and Ahmadirad (2018). An error occurs in the derivation of the average bit error rate (BER) of underwater wireless optical communication (UWOC) systems with on-off keying (OOK) intensity modulation, due to choosing a non-optimal decision threshold. The revised derivation is provided and substantiated by numeric simulation results.
查看更多>>摘要：A new type of dye laser is proposed based on a guided-mode resonance (GMR) transmission structure using coupled gratings. By distributing the laser dye in the coupled gratings, controllable transmission lasing behavior was simulated. The structure excites the transmission GMR effect and causes a strong local electric field in the coupled gratings, inducing the slow light effect, which in turn enhances the interaction between light and matter. The proposed GMR structure guides laser emission in the transmission direction. Two structures with resonant wavelengths of 820 nm and 870 nm were designed and compared. A higher laser intensity can be obtained in the structure with resonance at 870 nm and a corresponding threshold and half-height width of 1.24 x 10(7) V/m and 0.8 nm, respectively. In addition, the lasing wavelength can be tuned by changing the relative position of the coupled gratings. The proposed structure is desirable for the construction of other light-emitting devices.
查看更多>>摘要：In this work, we investigate improving spectral efficiency with direct detection based partial-response square shaping, which generalizes partial-response pulse shaping and reduces width of power spectrum of signal under both linear and non-linear model assumption. For linear model, quadrature point bias of Mach-Zender modulator is used. For non-linear model, null point bias of Mach-Zender is used, however, non-linear pre coding and equalization are required. By comparing results obtained with linear model and non-linear model, we identify the factors influencing performance of short reach transmission. Results of experiment over a 25 km dispersion uncompensated link show following: Under non-linear model, performance issue is revealed with non-linear optical channel. Under linear model, for PAM4 modified-duo-binary with bias signal and PAM4 duo-binary, 2 b/s/Hz is achievable with 7% overhead hard decision decoding. Also, PAM4 modified-duo-binary with bias signal has 1 order lower bit error rate than PAM4 duo-binary, while theoretical analysis confirms the finding for short reach transmission, that non-linear equalization can recover information from coherent item and can suppress interference caused by self-beat item.
查看更多>>摘要：The phenomenon of light scattering has brought challenges to many fields. In recent years, a novel method based on speckle-correlation has been proposed to look through scattering medium. However, the field of view (FOV) of this method is limited by the angular range of the optical memory effect (OME). In this paper, a polarization modulation-based method is proposed to look through the scattering medium beyond the OME range. This method can achieve single-shot non-invasive looking through multilayer scattering medium by using a polarization camera. Targets beyond the 4 times OME range is recovered by a single shot and a larger one also can be restored by moving the camera to collect the light signal. Unlike other methods that aim at imaging beyond OME, this method can reconstruct targets without reference points. The proposed method has no restriction on the target distribution, and both a single target or two separate targets can be recovered. The effectiveness of the method is verified through experiments.
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Elsevier