Abstract:In this paper, an arrayed liquid prisms system based on electrowetting-on-dielectric (EWOD) is proposed to modulate the three-dimensional beam steering control. The relationships between beam steering control range, electrowetting contact angle, and liquid refractive index are derived. COMSOL is employed to demonstrate the beam steering control properties of the electrowetting-based arrayed liquid prisms when bias voltages are applied. The influence of contact angle, liquid refractive index, and interval between adjacent prisms are discussed. The results show that the beam steering control performance of the system will be greatly improved, and the range of beam steering angle is −20° to 20° by selecting optimum combinations of liquids and rational interval between adjacent prisms. The arrayed liquid prisms system can succeed to achieve continuous control of beam steering in a conical region with an apex angle of 40°, and the vertex of the circular cone is located at the 15.02 mm in the z-axis. The proposed system will promote the development of non-mechanical beam steering technology and have a wide range of applications.

Abstract:Accurate values of masked detector signal (MDS) is the key to the correction capability of wavefront sensorless (WFSless) model-based adaptive optics (AO) system. However, imaging detectors always carry different kinds of noises in real applications, which make MDS deviate from theoretical results. Calculation errors of MDS suffered from the noise were analyzed through theory and simulation. Additionally, considering the method of threshold is usually used to mitigate the noise, we also discussed the influence of threshold on MDS. Results showed that the simulation is consistent with the theory and there exists an optimal threshold to make the error minimum for different noise. A fitting formula, which can accurately calculate optimal thresholds, was proposed based on the simulated data. Above results can provide a plausible method and theoretical basis to mitigate imaging noise of detectors in real applications.

Abstract:In this paper, we report the design and simulation of a bias-selectable dual-band photodetector operating in the visible (VIS) and near infrared (NIR) regions. The photodetector consists of two back-to-back avalanche photodiodes (APDs) with InGaAs and Si absorption layers respectively. The structure and electrical and optical properties of the dual-color photodetector were designed and simulated by exploiting Silvaco software. The results obtained on the basis of numerical simulation include the current-voltage, capacitance-voltage, spectral response, etc. The optical simulation shows the detection capability in the VIS and NIR ranges, cut-off wavelengths of 1.0 µm and 1.8 µm depending on the applied bias polarity. Comparing with using the PIN structure as element device, the dual-band photodetector based on the APD configuration could detect the very weak signal, realizing few photons, even single photon detection.

Abstract:Electro-optic Pockels cell are important opto-electronic devices for conduction of optical switching, optical modulation, where an electrical biasing signal acts on a polarized light passing through the system. Since last few decades lots of works are reported in this area. Again, it is observed that a good switching or modulation becomes realized if the depth of modulation is increased by increasing more phase difference between two orthogonal polarized components of light passing through the material against a biasing signal. Here in this paper the authors propose a new scheme, where multi-passing technique is used to create a high degree of phase difference between those two orthogonal polarized components of light against the biasing signal. The multi-passing of light through the material enables more and more optical path length for the light. So, more and more phase difference between the components of light beams, one passing outside the material and other passing through the material multiple times is created. This method ultimately generates a high degree of depth of modulation in optical switching.

Abstract:1.194 2×1014 W/m2. This work is helpful to further analyze the applications of fs laser processing. It provides guidance and reference for different kinds of fs laser processing methods.

Abstract:Fano resonance is realized theoretically in a photonic crystal. The structure is composed of a cavity side coupled to a partially transmitting waveguide. By optimizing the structure parameters, asymmetric sharp Fano resonance transmittance spectrum is achieved with quality factor of 2 213, extinction ratio of 57 dB and peak loss of 0.2 dB. The sharp spectrum can be used in sensor applications. Such as pressure sensor, the pressure sensitivity is about 9.15 nm/GPa. and for refractive index sensing application, the sensitivity is about 800 nm/RIU, and the maximum of figure of merit can reach 1 000. Besides, this sharp Fano resonance based on photonic crystal has potential applications in optical switches, filters etc. And it can be integrated into optical communications and optical integration circuits.

Abstract:In this work, we studied the effect of different pH values on morphology, band gap and photoluminescence (PL) properties of Eu3+/Tb3+ co-doped ZnO prepared by coprecipitation method. Experimental results show that alkaline condition is more favorable for the doping of Eu3+ and Tb3+ ions which reduce the band gap and increases the PL intensity of UV emission (385 nm) and visible emission (400—600 nm) of ZnO. Gaussian deconvolution PL spectra show that the defects on the surface of ZnO are decreased when it is synthesized under alkaline conditions. Furthermore, both the intrinsic orange emission of Eu3+ ions (611 nm) and the intrinsic green emission of the Tb3+ ions (495 nm) of ZnO in this case are obtained at the same time. High intensity green and orange emission indicates that Eu3+/Tb3+ co-doped ZnO is a promising PL material and has potential in emission devices.

Abstract:The fluorochloride glasses samples with good luminescent properties in the infrared region were successfully prepared by melt quenching method. The introduction of Cl- effectively improved the mid-infrared (MIR) luminescence of erbium-doped fluoride glass at 2.7 μm nearby. According to Judd-Ofelt theory, the increase in Ω2 after the introduction of Cl- indicates an increase in the asymmetry and covalence of the sample. X-ray diffraction (XRD), absorption spectrum, Raman spectroscopy, infrared Fourier (FTIR) and infrared fluorescence spectroscopy were specifically conducted. The emission cross section (1.04×10-20 cm2) and the absorption cross section (9.68×10-21 cm2) of the sample at 2.7 μm nearby were calculated by measurement. Therefore, non-oxide erbium-doped fluorochloride glass is a good luminescent material in the MIR band.

Abstract:A facile citric acid assisted sol-gel combustion method was performed to synthesize cobalt chromite (CoCr2O4) ceramic pigment. The effect of the annealing temperature on structure, morphologies, and optical properties of the prepared CoCr2O4 pigments were systematically studied by thermogravimetry, differential thermal analysis, X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The results show that CoCr2O4 spinel crystal was achieved after heat treatment of the as-burnt powder at a relatively low temperature (400 °C) and the average crystallite size of the CoCr2O4 pigment increased with the annealing temperature. Furthermore, on the CIE parameters of CoCr2O4 pigment, a and b values became much more negative with the annealing temperature due to much more Co2+ ions located in tetrahedral sites and much more Cr3+ ions located in octahedral sites. Finally, the measured solar absorptance indicates that this ceramic pigment is expected to fabricate the color paint coating for solar absorber application.

Abstract:The chromium (Cr) films on silicon Si(100) substrate are prepared using DC magnetron sputtering technique at an argon gas pressure of 3 Torr for different applied powers (40—140 W). The chemical composition, the thicknesses and the structural characterization of the deposited Cr films are studied and analyzed using energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and X-ray diffraction (XRD), respectively. Furthermore, the generated plasma parameters, including floating potential, plasma potential, electron density, ion density and electron temperature, have been measured, and the automated Langmuir probe is used for the Cr films deposition. The ion and metal fluxes are also determined. The results show that the Cr film thickness enhances with the higher applied power. The Cr deposited films properties are characterized and correlated with the measured plasma parameters.

Abstract:A novel phase noise (PN) compensation algorithm based on the decision feedback (DF) algorithm and the linear combination self cancellation (LCSC) algorithm is proposed to improve the system performance degradation caused by laser linewidth in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. In this proposed LCSC-DF algorithm, the LCSC algorithm is used to precode the subcarrier information at the transmitter and decode the demodulation information and inter-carrier interference (ICI) related information at the receiver. And then the pilot information is used to obtain the final compensation signal by the improved DF algorithm. The simulation results show that the PN compensation performance of the proposed LCSC-DF algorithm is better than that of the DF algorithm. Furthermore, with the increase of the signal to noise ratio (SNR), its bit error rate (BER) performance approaches to that of the SC-DF algorithm at the larger PN linewidth. The subcarriers utilization ratio of the proposed algorithm is higher than that of the SC-DF algorithm. As a result, the proposed algorithm can effectively improve the performance of the system.

Abstract:Multimode fiber has a richer spatial dimension than single-mode fiber, and is an ideal platform for studying many novel nonlinear effects. We established a strong linear coupling and short-range fiber model to understand the interactive effects of linear coupling and nonlinear effects. We find that strong linear coupling can compensate for the group delay between eigenmodes and cause energy fluctuation between modes which weakens the nonlinear effects. In high energy pulses, the interaction of linear coupling and nonlinear effects can help producing weak dispersion waves when the spectrum is broadened. Since linear coupling in a mode group is common and unavoidable, these results may provide a certain theoretical explanation for multi-mode nonlinear phenomena.

Abstract:In this paper, a new two-dimensional variable weight optical orthogonal code (2D-VWOOC) for optical code division multiple access (OCDMA) system is constructed. It takes the C as the frequency hopping sequence and the strict variable weight optical orthogonal code (SVWOOC) as the time spreading sequence. The code can meet the different quality of service (QoS) requirements of different users. Under the same time spread sequence, the bit error rate (BER) of QCHC/SVWOOC is 3~9 orders of magnitude lower than that of other similar 2D-VWOOCs. In Optisystem simulation, when the transmission rate of the system is 14 Gbits/s, the BER of users with code weight 4 is 7 orders of magnitude lower than that of users with code weight 2, and a clear and correct eye diagram can be obtained.

Abstract:In order to avoid the effect of photon defect on the imaging during X-ray generation, an imaging integral filter based on quantum enhancement was proposed in this paper to effectively reduce the sensitivity of X-ray detection system for quantum noise. Firstly, the coupling constraint at the end of the image intensifier was analyzed by discussing the X-ray imaging mechanism. The effects of quantum thermal noise and defects on spectrum transfer were studied from the micro perspective. Then the effectiveness of the new integral filter method was verified from the view of the integral effect of fundamental space frequency transfer characteristics in Fourier spectrum. Finally, the superiority and real-time performance of the quantum enhancement filter method were verified by the comparison filter testing.

Abstract:This paper proposes an efficient method for defect detection of magnetic disk image based on improved convolutional neural network. We build a model named DiskNet on the basis of VGGNet-19, in which the optimal activation function is selected predictively through a weighted probability learning curve model (WP-Model). First, we use Markov Chain Monte Carlo (MCMC) to infer the predicted value and determine prediction probability. Then, the evaluation point (EP) is determined by the effective information of training curve. In the process of DiskNet training, when the prediction probability is higher than the threshold, the neural network will select the current activation function. If the training epochs exceed the EP and the threshold is not reached, the original activation function will be used. The experimental results show that the accuracy of the proposed method in detecting defects on the magnetic disk image data set is 96.9%.