Abstract:In order to meet the requirements of the high gain and wide field of view (FOV) for indoor visible light communication (VLC) system, a new optical receiving system is proposed, which integrates a Fresnel lens with a hemispherical lens. The effects of the two lenses’ spacing and the radius of the hemispherical lens on the optical gain at different FOV are investigated. As the FOV increases, the designed antenna displays enhanced reception performance compared with the traditional receiving optical antenna. The optical gain of the designed antenna is 6.88 in the condition of FOV of 40°. To further verify the rationality of the designed antenna, a model of VLC system is established based on the designed antenna in a room with a size of 5 m×5 m×3 m. The results show that the received average power using the designed antenna increases by 22.81 dBm, and the average signal to noise ratio (SNR) is 2.3 times of that without any optical antenna. The designed antenna is promising for the application in indoor VLC systems.

Abstract:Based on free space laser communication, this article describes the working principle of electro-optical frequency shifting, designs an optical adaptive filtering module, and builds the core module of the dynamic optical Doppler shifting simulator for laser channel. It is expected to be applied to the heaven-ground integrated communication link. In this article, we adopt the electro-optical frequency shifting technique combined with the microwave-light wave. In the 1 550 nm band, the negative feedback algorithm is used to complete the adaptive filtering, which realizes optical Doppler frequency shifting and high-precision locking. The frequency shift range reaches +5.5—+32 GHz, and the analog precision is better than 645 Hz. When the microwave frequency is greater than 13.5 GHz, the signal-to-noise ratio (SNR) of the output optical power reaches 20 dB, which lays the foundation for the next stage space laser communication.

Abstract: The transmission sinusoidal grating (TSG) shows a different diffraction pattern with conventional black-white transmission grating (BWTG), which can focus the diffraction energy on a higher order and has been widely used in the spectrum instruments. According to the description of the scalar diffraction theory, the numerical simulation for diffraction properties of the TSG has been studied for years. However, the fabrication of the TSG is difficult and seldom reported. In this article, a TSG is designed and an approach of the X-ray LIGA process is used to fabricate the TSG and the device can obtain the brightest diffraction peaks at the ±1 order with the zero-order diffraction peak unobvious on the background for a certain wavelength of the incident light.

Abstract:An automated flow-batch analyzer (FBA) based on spectrophotometry was developed for the determination of nitrite (NO2−) in environmental waters. The FBA consists of a homemade flow cell, light source, detector and a mini-syringe pump, which was controlled by self-designed software written in LabVIEW. Two LEDs and a light-to-voltage converter were used as the light source and detector respectively. The chemical detection method was based on spectrophotometry and modified Griess reaction. With the optimized conditions, the limit of detection (LOD) was 0.018 µmol∙L-1 and the relative standard deviations (RSDs) at different concentrations (0—12 µmol∙L-1) were 0.54%—3.63% (n=3). Measurements of different aqueous samples (n=21) showed no significant difference between results obtained by developed FBA and a commercial spectrophotometer.

Abstract:In this study, the conversion efficiency (CE) of a core/shell quantum dot (QD) with type-II structure is studied by the detailed balance model. In particular, a size dependent strain effect caused by the lattice mismatch is considered since the CE under the detailed balance model is strongly dependent on the band gap of materials. The results show that the strain effect has a very important influence on the CE, and the multiple exction generation (MEG) can significantly increase the CE, so it must be considered in such a low-dimensional system.

Abstract:We fabricated phosphorescent organic light-emitting diodes (PhOLEDs) using thermally activated delayed fluorescence (TADF) material 10,10'-(4,4'-sulfonylbis(4,1-phenylene)) bis(9,9-dimethyl-9,10-dihydroacridine) (DMAC-DPS) with low concentration, which showed better performance compared with 1,3-bis(carbazole-9-yl) benzene (mCP) based devices. When the concentration of DMAC-DPS was 1wt%, the driving voltage of the device was only 3.3 V at 1 000 cd/m2, and the efficiency and lifetime of the device were effectively improved compared with those of mCP based devices. The result indicated that DMAC-DPS could effectively improve the performance of phosphorescent devices. We believe that the better device performance can be attributed to the optimization of the energy transfer process in the emitter layer and lifetime of triplet excitons by DMAC-DPS. The study may provide a simple and effective strategy to achieve high-performance OLEDs.

Abstract:In this paper, a transmissive terahertz (THz) quarter wave plate (QWP) has been proposed to realize the linear-to-circular polarization conversion in terahertz range. This quarter wave plate is composed of two dielectric layers and one metallic layer with asymmetric cross slots. In the range of 0.894—1.378 THz, the axis ratio of proposed device is less than 3 dB, and its polarization conversion efficiency is more than 45%. The distributions of surface currents and electromagnetic field density had been proposed to understand the physical mechanism of proposed device. The linear-to-circular polarization conversion can be attributed to the asymmetric transmission along slots. Finally, the simulation results are validated by experiments in terahertz region. The proposed device has simple geometry and good performance, which can be used as a key component in applications of terahertz communications, terahertz imaging and terahertz sensing.

Abstract:Indium tin oxide (ITO) thin film was deposited on glass substrate by means of vacuum evaporation technique and annealed at 200 °C, 300 °C and 400 °C in air for 1 h. The characterization and properties of the deposited film samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-VIS-NIR spectroscopy techniques. From the XRD patterns, it was found that the deposited thin film was of crystalline at an annealing temperature of 400 °C. The crystalline phase was indexed as cubic structure with lattice constant and crystallite size of 0.511 nm and 40 nm, respectively. The SEM images showed that the films exhibited uniform surface morphology with well-defined spherical grains. The optical transmittance of ITO thin film annealed at 400 °C was improved from 44% to 84% in the wavelength range from 250 nm to 2 100 nm and an optical band gap was measured as 3.86 eV. Hall effect measurement was used to measure the resistivity and conductivity of the prepared film.

Abstract:An all-optical wavelength reuse technique employing cost effective power efficient vertical surface emitting laser (VCSEL) is proposed to address uplink data streaming from end-users by exploiting the same wavelength assigned to them. A saturated optical erbium-doped optical fiber amplifier (EDFA) is adopted to erase a directly modulated 10 Gbit/s data from an incoming downstream wavelength. We show that with EDFA saturation, the extinction ration of the incoming wavelength is reduced to less than 1 dBm, therefore allowing for wavelength re-modulation. A receiver sensitivity of −19.65 dBm and −17.86 dBm is attained for downstream and upstream data signals respectively. A total of 24.7 km single mode fibre transmission is attained experimentally. This technique opens new perspectives towards development of efficient spectrum utilization for application in wavelength flexible optical networks with non-static flex-spectrum grids.

Abstract:Although optical camera communication (OCC) is gaining increasing attention in research, developing a practical OCC system to increase data rate and transmission distance is still an issue. The rolling shutter can increase data rate, but it also limits the transmission distance at the same time. When the transmission distance is long, the thresholding method will become difficult and the block sequence number (BSN) is easy to be wrong due to bit errors, which will make it impossible to reorder the frame sequences. In this paper, in order to increase the transmission distance, we propose the efficient thresholding method which transforms partial mean gray values of per column nonlinearly to increase the contrast between light and dark bands. In addition, this method takes the frame image of the camera as the basic unit to adjust the threshold for the environment in which each frame of the image is located. Experimental results show that this method is better than the polynomial regression. Moreover, we perform the error correction of BSN by using its continuity to specify the legal BSNs and the illegal BSNs.

Abstract:The tracking performance of star sensor degrades seriously under dynamic conditions. To improve the tracking accuracy and efficiency, an attitude tracking method based on unscented Kalman filter (UKF) and singular value decomposition (SVD) is proposed in this paper. The star sensor is modeled as a nonlinear stochastic system, the state of which is attitude quaternion. The quaternion can be estimated by UKF, then the predicted attitude and corresponding star positions are obtained. To ensure the stability of attitude tracking, SVD is applied to obtain the sigma points in UKF continuously. The experimental results indicate that the proposed method yields high accuracy and efficiency in attitude tracking. This method provides a practical approach to ensure the tracking performance of star sensor under dynamic conditions.

Abstract:In this paper, a new algorithm is proposed to remove the effects of aerodynamic optical thermal radiation from a single infrared image. In this method, the joint probability model of gradient distribution is introduced by studying the "global smoothing and local fluctuation" characteristics of the bias field. A prior L0 norm of dark channel is introduced to constrain the latent clear image. Finally, the split Bregman method is used to solve the optimization problem. The effectiveness of the proposed method is verified by a series of experiments, and the results are compared with the results of the existing methods for the correction of thermal radiation effects.

Abstract:Glaucoma as an irreversible blinding opioid neuropathy disease, its blindness rate is the second only after cataract in the world. The optic cup-to-disc ratio (CDR) is generally considered to be an important clinical indicator for judging the severity of glaucoma by ophthalmologists from retinal fundus image. In this letter, we propose an automatic CDR measurement method that consists of a novel optic disc localization method and a simultaneous optic disc and cup segmentation network based on the improved U shape deep convolutional neural network. Experimental results demonstrate that the proposed method can achieve superior performance when compared with other existing methods. Thus, our method can be used as a powerful tool for glaucoma-assisted diagnosis.

Abstract:In this paper, a novel energy functional minimization model is proposed for ultrasound images denoising. A controllable regularized term and the variational method are employed in the process of speckle noise. This model not only improves the plasticity of the model, but also improves the effect and efficiency of noise removal. The new model has different diffusion performance in different regions. At the same time, the diffusion performance is related to the parameters introduced by the proposed model. Numerical simulation results show that different parameters have different denoising effects, and the proposed model for speckle noise removal is superior to traditional models.

Abstract:With the development of China's high-resolution special projects and the rapid development of commercial satellite, the resolution of the mainstream satellite remote sensing images has reached the sub-meter level. Ship target detection in high-resolution remote sensing images has always been the focus and hotspot in image understanding. Real-time and effective detection of ships play an extremely important role in marine transportation, military operations and so on. Firstly, the full-factor ship target sample library of high-resolution image is synthetically prepared. Then, based on the Faster R-CNN framework and Resnet model, optimize the parameters of the model to achieve accurate results. The simulation results show that the detection model trained in this paper has the highest recall rate of 98.01% and false alarm rate of 0.83%. It can be applied to the practical application of ship detection in remote sensing images.

Abstract:An abundance estimation algorithm based on orthogonal bases is proposed to address the problem of high computational complexity faced by most abundance estimation algorithms that are based on a linear spectral mixing model (LSMM) and need to perform determinant operations and matrix inversion operations. The proposed algorithm uses the Gram-Schmidt method to calculate the endmember vector set to obtain the corresponding orthogonal basis set and solve the unmixing equations to obtain the eigenvector of each endmember. The spectral vector to be decomposed is projected onto the eigenvector to obtain projection vector, and the ratio between the length of the projection vector and the length of the orthogonal basis corresponding endmember is calculated to obtain an abundance estimation of the endmember. After a comparative analysis of different algorithms, it is concluded that the proposed algorithm only needs to perform vector inner product operations, thereby significantly reducing the computational complexity. The effectiveness of the algorithm was verified by experiments using simulation data and actual image data.