International Journal of Optics

In the free-space optical (FSO) communication system, alignment and coupling are key issues. In this work, we adopt a PIN photodiode board as the new receiver to address this question. Firstly, with rapid thermochemical vapor deposition (RTCVD) and solar cell technology, the PIN photodiode board is manufactured. Then, using scanning electron microscope (SEM) and transmission electron microscope (TEM), the microphotographs of the PIN photodiode are taken. After that, the PIN board is arranged as a new receiver in the FSO system to do a bit error rate (BER) experiment. In total, we have carried out 4 groups of experiments. The BERs of the ordinary receiver are as follows: (10^−8.5, 10⁻⁸, 10⁻⁸, and 10^−7.9) and that of the new receiver is (10^−9.2, 10^−9.1, 10^−9.1, and 10⁻⁹), respectively. It means the BER of the new receiver is lower. In other words, the new receiver performs better.

High-visibility pseudothermal light source is required by the long-distance ghost imaging technology. In this article, the pulsed pseudothermal light based on a compact and Q-switched laser system with high peak power and intensity is reported. The passively Q-switched technique advances the performance of the pseudothermal light, where the second-order quantum correlation function value increased from 1.452 to 1.963.

For mobile robots and location-based services, precise and real-time positioning is one of the most basic capability, and low-cost positioning solutions are increasingly in demand and have broad market potential. In this paper, we innovatively design a high-accuracy and real-time indoor localization system based on visible light positioning (VLP) and mobile robot. First of all, we design smart LED lamps with VLC and Bluetooth control functions for positioning. The design of LED lamps includes hardware design and Bluetooth control. Furthermore, founded on the loose coupling characteristics of ROS (Robot Operator System), we design a VLP-based robot system with VLP information transmitted by designed LED, dynamic tracking algorithm of high robustness, LED-ID recognition algorithm, and triple-light positioning algorithm. We implemented the VLP-based robot positioning system on ROS in an office equipped with the designed LED lamps, which can realize cm-level positioning accuracy of 3.231 cm and support the moving speed up to 20 km/h approximately. This paper pushes forward the development of VLP application in indoor robots, showing the great potential of VLP for indoor robot positioning.

We present the results of the development of a representational model of the multispectral polarization state analyzer of the ScanPol scanning polarimeter for the space experiment Aerosol-UA. The aim of the Ukrainian space mission Aerosol-UA is to create a database based on continuous satellite measurements of the optical characteristics of aerosol and cloud particles in the Earth’s atmosphere over a long period of time. The ScanPol polarimeter is designed to acquire spatial, temporal, and spectral-polarimetric measurements simultaneously to minimize instrumental “parasitic” effects and effects of “false” polarizations due to scene movement. Simultaneity is provided by separation of the initial spatial field by a pair of conjugated telescopes and a pair of Wollaston prisms. ScanPol provides to measure the first three Stokes parameters I, Q, and U of the radiation reflected by atmospheric aerosols and the Earth’s surface for a six solar reflectance spectral bands in the near ultraviolet (NUV), visible (VIS), and near-infrared (NIR) spectral channels centered in the wavelengths 370 nm, 410 nm, 555 nm, 865 nm, 1378 nm, and 1620 nm. Stokes parameters I, Q, and U are used to determine a degree of linear polarization of radiation that will allow obtaining the phase function and polarization characteristics of aerosol particle scattering, estimate their size, and determine the aerosol type and optical thickness. The polarimeter optical layout is considered, and the spectral characteristics of the transmission of optical channels are given. Obtained signal-to-noise ratio exceeded 500 for wavelengths 370 nm and 410 nm and exceeded 1000 for other wavelengths. The design of the chosen photodetectors is based on surface mount type photodiodes: Si-photodiodes Hamamatsu S10356-01 for the optical range of 370–860 nm and InGaAs-photodiodes Hamamatsu G8941-011620 for wavelengths 1378 nm and 1620 nm. The effect of orientation of Wollaston prisms axes on polarization measurement error is considered. The errors of azimuth mount of Wollaston prisms ≤2 arcmin in ScanPol leads to error of degree of linear polarization ≤0.0012.

This study was conducted to verify how the illuminance and correlated color temperature of LED lighting affect working memory. For this study, an automatic LED lighting device based on a light sensor was developed and used, and the lighting conditions were treated with a total of six conditions (2 × 3): two illuminance conditions (dim: 400 lx, bright: 1,000 lx) and three correlated color temperature conditions (3,000 K, 5,000 K, and 7,000 K). There were 30 participants in the study, and the average age was 21.6 years (Standard deviation = 1.92). Participants were assigned to all six lighting conditions, and the placement order was randomized. For the measurement of working memory, 3-back task was used and the correct responses for 5 minutes were used as a dependent variable. As a result of repeated measures analysis of variance (ANOVA), both illuminance and correlated color temperature were found to be significant variables affecting working memory, and no interaction effect between illuminance and correlated color temperature was found. As a result of the post hoc verification conducted thereafter, the working memory performance in the bright light condition (1,000 lx) was 48.32 (Standard deviation = 15.63) on average, compared to 44.80 (Standard deviation = 15.29) in the relatively dim condition (400 lx). It was found that the condition of bright light was superior in performing working memory compared to relatively dim condition. The working memory performance in the correlated color temperature condition (5,000 K) was 48.32 (Standard deviation = 16.41) on average and higher than that of other color temperature conditions. As a result, working memory performance was the best in 1,000 lx, 5,000 K condition Mean = 53.43 (Standard deviation = 18.38), and 400 lx, 7,000 K condition Mean = 42.73 (Standard deviation = 17.68) showed the worst performance of working memory.

In this paper, an image encryption algorithm based on a hyperchaotic system and variable-step Josephus problem is proposed. Based on an in-depth analysis of the classic Josephus problem, a new variable-step Josephus problem that combines the pseudorandom sequence with the Josephus problem is proposed. Firstly, the hash value of the plaintext image is calculated, which is converted to the initial value of the chaotic system. Secondly, the chaotic system is iterated to generate four pseudorandom sequences X, Y, Z, and W. The sequences X, Y, and Z are input as parameters into the variable-step Josephus function to scramble the positions of the rows, pixel bits, and columns of the image, respectively. Finally, the elements of the sequence W and the image pixels are used to perform the addition operation. According to the experiments, the information entropy of the encrypted image with size 256256 reaches 7.997 and the adjacent correlations in three directions are within ±0.01. The experimental results show that image encryption algorithm proposed in this paper has plaintext sensitivity and can resist the common attacks.