Abstract:A time-differential imaging method using a dual-line-array time delayed and integration (TDI) CCD optical camera is proposed in this paper, precisely measuring the motion parameters of the dynamic aircraft. Firstly, based on the spatiotemporal information of the aircraft obtained by the optical satellites, the velocity on the image plane and the twice imaging time interval are calculated. The improved scale-invariant feature transform (SIFT) algorithm that integrates the aerodynamic configuration of the aircraft is proposed to extract the region of interest. After that, the geometric centers of the aircraft images are determined with the median method, and then the velocity vector of the aircraft can be obtained by synthesizing a variety of spatial parameters and mathematical techniques. Finally, using the snapshots of the dynamic aircraft in the area of Harbin captured by the commercial satellite JL-1, the calculated results are quite close to its actual motion characteristics, which verify our method. This paper plays a guiding role in the evaluation and surveillance of dynamic aircraft.

Abstract:This paper analyzes and demonstrates a simplified frequency quadrupling configuration for optical millimeter-wave (mm-wave) generation, in which the electrical phase shifter and optical filter are omitted. Theoretical analysis is given to reach the optimum operating conditions including direct current (DC) bias voltage, optical transmission point of the dual-parallel Mach-Zehnder modulator (MZM) bias voltage, optical transmission point of the dual-parallel Mach-Zehnder modulator (DP-MZM), amplitude of the radio frequency (RF) driving signal and the impact of the extinction ratio (EF) on the optical sideband suppression ratio (OSSR) and radio frequency spurious suppression ratio (RFSSR). Experiments prove an OSSR of 15 dB and an RFSSR of 26 dB for the new frequency quadrupling scheme at 6 GHz, 8GHz and 10 GHzof RF driving signal without any electrical phase shifter or optical filter. This system exhibits the advantage of low wavelength dependence and large frequency tunable range.

Abstract:Optical power cable (OPC) current sensing models and experiments based on the optical transmission properties of magnetic fluids are proposed. Firstly, the models of OPC, magnetic fluid current sensor and OPC current sensing are established. Secondly, the relationship between the magnetic field and the current of the OPC is demonstrated. Finally, the relationship between the optical transmission properties of magnetic fluids and the OPC current is studied. The results show that there is a good linear relationship between the transmitted power and the current of the OPC.

Abstract:The Stokes line of multi-mode Raman laser was limited by low conversion efficiency of higher-order Stokes and the competition between pure cascaded stimulated Raman scattering (SRS) and Four-wave-mixing (FWM) process which will deplete the pump of SRS process. Through developed pulse-train synchronously pumping technique and two-Raman-mode operating, the orders of output Stokes was improved. With average power of 220mW, the developed a Raman laser providing up to 5 orders Stokes output, containing up to 16 laser lines without tuning operating and four-wave-mixing process.

Abstract:To meet the needs of terahertz imaging and communication, a 420-GHz on-chip antenna (OCA) with high gain and high radiation efficiency is designed using a standard 55 nm CMOS technology. In the proposed OCA structure, the substrate integrated waveguide (SIW) antenna forms a back cavity to suppress the surface waves and separate the radiation aperture from the low-resistivity substrate. To increase the efficiency of OCA, a single-layer quartz superstrate is proposed. An analytical model to calculate the radiation efficiency is presented, and a detailed design approach is described. The proposed antenna is simulated using Ansoft HFSS. The simulated antenna has a maximum gain of 4.9 dBi and a radiation efficiency of 76.27%. The bandwidth of S11 below −10 dB is 44 GHz. The OCA has good performance and can be widely used in terahertz imaging and communication.

Abstract:Based on the density functional theory with hybrid functional approach, we calculated the structural, electronic, and the optical properties of Cu2MgSn(S1-xSex)4 (CMTSSe)，an potential photovoltaic material for thin film solar cells. The calculation reveals a phase transition from kesterite to stannite structure when Zn atoms are substituted by Mg atoms. In particular, the S-to-Se ratio can determine the energy splitting between the electronic states at the top of the valence band. The band gaps of CMTSSe can be tuned in the ranges of 1.01—1.58 eV. Calculated optical properties and tunable band gaps make them beneficial for achieving band-gap-graded solar cells.

Abstract:This paper proposes a novel photonic crystal optical fiber which can support 30 orbital angular momentum (OAM) modes transmission and possesses relatively flat and low dispersion. The OAM modes can be well-separated due to the large effective refractive index difference (above 10-4) between the eigenmodes. The only material of the designed fiber is silica. The dispersion of each OAM mode is controlled in the range of 50—100 ps.nm-1.km-1 and the total dispersion variation is below 10 ps.nm-1.km-1 from 1 500 nm to 1 600 nm. Moreover, the confinement loss of each OAM mode is below 8.17×10-10 dB/m at 1 550 nm, and the nonlinear coefficients is less than 0.71 W-1/km for all modes at 1 550 nm. With all these good features, this proposed optical fiber is promising to be applied in fiber-based OAM communication systems.

Abstract:We experimentally demonstrate the all-optical efficient technique for dynamic full-duplex wavelength routing and reach extension through adoption of passive fibre Bragg grating (FBG), energy efficient vertical cavity surface emitting lasers (VCSELs) and high gain forward Raman pump. In this study, two VCSEL channels at 1 549.62 nm and 1 550.01 nm are directly modulated with a 8.5 Gbit/s data signal each, and transmitted over 25.5 km fibre to a passive single mode FBG-based wavelength routing node. The precise wavelength selectivity of the FBG is exploited to achieve all-optical real-time wavelength routing of the 1 549.62 nm VCSEL channel with a maximum insertion loss of 22.1 dB. The 1 550.01 nm channel is transmitted through the FBG with a maximum penalty of 1.03 dB. By utilizing the 7.2 dB flat gain of a forward Raman pump, the routed 1 549.62 nm VCSEL channel is transmitted over 76.7 km fibre with a maximum penalty of 3.84 dB at bit error rate (BER) of 5-5. Our technique is all-optical, power efficient as it employs passive FBG and circulators and has low cross talk allied to precise wavelength selectivity of the technique.

Abstract:In this paper, a visual focus of attention (VFOA) detection method based on the improved hybrid incremental dynamic Bayesian network (IHIDBN) constructed with the fusion of head, gaze and prediction sub-models is proposed aiming at solving the problem of the complexity and uncertainty in dynamic scenes. Firstly, gaze detection sub-model is improved based on the traditional human eye model to enhance the recognition rate and robustness for different subjects which are detected. Secondly, the related sub-models are described, and conditional probability is used to establish regression models respectively. Also an incremental learning method is used to dynamically update the parameters to improve adaptability of this model. The method has been evaluated on two public datasets and daily experiments. The results show that the method proposed in this paper can effectively estimate VFOA from user, and it is robust to the free deflection of the head and distance change.

Abstract:The difficulty of build-up area extraction is due to complexity of remote sensing data in terms of heterogeneous appearance with large intra-class variations and lower inter-class variations. In order to extract the built-up area from Landsat 8-OLI images provided by Google earth engine (GEE), we propose a convolutional neural networks (CNN) utilizing spatial and spectral information synchronously, which is built in Google drive using Colaboratory-Keras. To train a CNN model with good generalization ability, we choose Beijing, Lanzhou, Chongqing, Suzhou and Guangzhou of China as the training sites, which are very different in term of natural environments. The ArcGIS-Model Builder is employed to automatically select 99 332 samples from the 38-m global built-up production of the European Space Agency (ESA) in 2014. The validate accuracy of the five experimental sites is higher than 90%. We compare the results with other existing building data products. The classification results of CNN can be very good for the details of the built-up areas, and greatly reduce the classification error and leakage error. We applied the well-trained CNN model to extract built-up areas of Chengdu, Xi’an, Zhengzhou, Harbin, Hefei, Wuhan, Kunming and Fuzhou, for the sake of evaluating the generalization ability of the CNN. The fine classification results of the eight sites indicate that the generalization ability of the well-trained CNN is pretty good. However, the extraction results of Xi’an, Zhengzhou and Hefei are poor. As for the training data, only Lanzhou is located in the northwest region, so the trained CNN has poor image classification ability in the northwest region of China.

Abstract:For the ghost in visual background extractor (ViBe) algorithm and the influence of dynamic background, an improved ViBe algorithm is proposed to extract moving object in this paper. The way of background acquisition during modeling is improved to eliminate the ghost. Detect the saliency of the pre-M-frame, and synthetic relatively real background. Modeling with the background can avoid the generation of ghost. The selection of thresholds in the model is improved to reduce the impact of the dynamic background. Adjust the thresholds adaptively according to the background complexity. In addition, find the inner contour of extracted object to fill, which makes the detected targets more complete. Experimental results show that the presented algorithm effectively removes ghosts and enhances anti-interference ability. Compared with several existing methods, the presented algorithm has better performance.

Abstract:A high-speed fringe projection profilometry employing defocused binary fringe is presented to record the 3-D sign language, including gesture and mouth movement, to help people learn the sign language. It employs a number of advanced approaches, such as fringes binarization and defocus method, high precision phase calculation based on the phase-shifting method and the three pitches heterodyne unwrapping (TPHU) method, and how to combine multiple binary fringes into a 24-bit fringe. Experiments have shown that the proposed system can acquire and display high-quality 3D gesture and mouth movement at a speed of 500 frames per second.

Abstract:Optical interferometry can be applied to obtain the wavefront phase and reconstruct the three-dimensional wavefront by analyzing interference fringes. Single interferogram analysis based on two-dimensional Fourier transform is proposed. This method just needs to acquire and analyze single interferogram to solve the wavefront phase. Compared with phase-shift method, Single interferogram analysis can reduce experiment cost and the limitation of measuring environment like vibration, airflow and noise, and meet the requirement of real-time and dynamic interferometry. Because the wavefront phase information is included in the carrier frequency components of single interferogram, an image edge detection method is used to automatically extract the center and boundary of the first-order carrier component of the spatial spectrum of the interferogram in the frequency domain.