Juncai Yang

Non-line-of-sight multiscatter propagation model

A propagation model that describes the characteristics of multiscatter radiation in atmosphere is presented. The model is based on the Monte Carlo method; each scattering process is set as an event of probability. LOWTRAN7 is used to calculate the atmospheric coefficients, and Mie theory is used to calculate the scattering characteristics of the particles. It is shown that the multiscatter model matches the single-scatter model perfectly when the scattering count is 1, and the formula for the single-scatter approximation is modified for the non-line-of-sight (NLOS) problem. It is also shown that the duration of the impulse response is about 8 micros, the proportion of single-scatter irradiance is very small, and the average scattering count is 3.85 instead of 1 when the range is close to 1 km (weather conditions, field of view, and elevation angle are given). All these characteristics are presented for what is, to our knowledge, the first time. This model is wavelength-independent; 0.254 microm is chosen as the wavelength of simulation.

Study of effects of obstacle on non-line-of-sight ultraviolet communication links

This paper studies the effects of the obstacle on non-line-of-sight ultraviolet communication links using multiple-scatter model based on a Monte Carlo method. On the condition that transmitter beam and receiver FOV just pass the top of the obstacle, and ranges is fixed, the received energy density is at its maximum. The path loss increases when the transmitter or the receiver is much near to the obstacle, because the nearby common scattering volumes decrease intensively. The optimal received range decreases with the increasing of the distance between transmitter and obstacle. The predictions are validated with experimental measurements. This work can be used for the guidance of UV system design and network technology to apply in complex surroundings, such as mountain, buildings, etc.

Angular velocity estimation from measurement vectors of star tracker

In most spacecraft, there is a need to know the crafts angular rate. Approaches with least squares and an adaptive Kalman filter are proposed for estimating the angular rate directly from the star tracker measurements. In these approaches, only knowledge of the vector measurements and sampling interval is required. The designed adaptive Kalman filter can filter out noise without information of the dynamic model and inertia dyadic. To verify the proposed estimation approaches, simulations based on the orbit data of the challenging minisatellite payload (CHAMP) satellite and experimental tests with night-sky observation are performed. Both the simulations and experimental testing results have demonstrated that the proposed approach performs well in terms of accuracy, robustness, and performance.

Vectorized polarization-sensitive model of non-line-of-sight multiple-scatter propagation.

The existing Monte-Carlo-based non-line-of-sight (NLOS) multiple-scatter propagation model is extended to include polarization and also vectorized to improve the simulation speed by about 500 times. This model is validated by the noncoplanar single-scatter model; the results show a perfect match. Numerical examples for various polarization setups are obtained, and results show that the single-scatter and multiple-scatter signals are all polarization dependent. Therefore, NLOS polarized UV communication with a high data rate is achievable--the polarizing information is coded by a time-dependent polarizer, influenced by the atmospheric channel, and decoded according to the distribution characteristics of the scattered signals after the time-independent analyzers.

Theoretical evaluation of scattering effect on retroreflective free-space optical communication

Retroreflective free-space optical (RFSO) communication is a new concept of optical communication; it consists of an optical transceiver and a retromodulator and has advantages such as light weight, small volume, and low power consumption. The power captured by the receiver consists of two parts: retroreflective and scattering. The retroreflective characteristics are obtained using an analytical formula, the scattering characteristics using a Monte Carlo model. Results show that the scattering power plays an important role in a RFSO communication link, especially when the communication range is long or the meteorological range is short. Some rules are also obtained for the sake of system design, which include increasing the range from the transmitter and the receiver properly, increasing the area of the retromodulator, limiting the field of view of the receiver, and limiting the beam divergence of the transmitter.

Unexpected irreversible damage of an asymmetric bismuth silicate photorefractive spatial light modulator

Unexpected irreversible damage occurred repeatedly in the asymmetric bismuth silicate (BSO) photorefractive spatial light modulator under some operation modes, even though the power of the write-light beam does not exceed the optical damage threshold. According to the microscopic surface images and the Raman spectra of the BSO film, sudden rising of temperature in local areas caused by the drift of the photon-induced electrons is responsible for the damage; the damage exists not only on the surface but also inside the BSO crystal. The damage is relative to the structure of the spatial light modulator, the operation mode, and the growth of the BSO crystal. The information provided by the damage is useful for optimizing the structure, the operation modes, and the performance of the photorefractive spatial light modulators.

Characteristics of non-line-of-sight polarization ultraviolet communication channels

This paper investigates characteristics of polarization in non-line-of-sight (NLOS) ultraviolet (UV) communication channels based on a vectorized polarization-sensitive model of NLOS multiple-scatter propagation. The degree of polarization has been analyzed from the following factors: elevation angles, beam angle, field-of-view, off-axis angles, and baseline distance, etc. We draw conclusions that will guide the design of polarization multiplexing technology in NLOS UV communication systems. Outdoor experimentation has validated that this technology is useful to improve the data rate.

The experimental research of UV communication

Ultraviolet light communication is a new means of optical information transmission technology developed since 1990’s. In this paper, some key technologies developed from the experiment will be described in detail. These technologies include the design of high speed UV source frequency modulator, the design of high sensitive optical receiver system and the design of weak signal detect and process modular, etc. The UV communication system has accomplished good voice and high speed digital data bidirectional communication in semi-duplex way and its maximal communication baud rate is up to 9600 bps which is twice as the baud rate of the UV communication system made by GTE Company for navy USA navy in 2000. Furthermore, in some distance the system can achieves a non-line-sight communication.

Study on the heterodyning scattering of retroreflective free-space optical communication with optical heterodyning.

Retroreflective free-space optical communication is important because of advantages such as small volume, low weight, and low power consumption. Link failure caused by bad weather conditions will occur because of the attenuated retroreflective signal and the increased scattering of the transmitted light. The scattering effect can be reduced because the physical properties (including polarization, wavefront, and phase) of the scattering signal are different from those of the retroreflective signal. The physical properties of the scattering signal are obtained using a polarization-sensitive Monte Carlo model, and the heterodyning scattering signal is obtained using heterodyning theory. Results show that, with optical heterodyning, the scattering effect is efficiently reduced, and advantages such as better adaptability to bad weather conditions, longer communication range, more compact transceiver design, larger covering area of the optical receiver, and easier target acquisition for the retromodulator than before can also be obtained.

Design of MacNeille Polarizing Beam Splitter

MacNeille polarizing beam splitters(PBSs) has become important optical components in many optical systems. The principle of this type polarizing beam splitters was discussed in detail. It was found that the number of layers of a thin-film assembly, match of refractive index, and shift of reference wavelength are important parameters in designing MacNeille polarizing beam splitters. With the help of numerical simulation, the effect of these parameters on the properties of MacNeille polarizing beam splitters was estimated detailedly. The results show that the transmittance rises gradually for p-polarized light whereas decreases for s-polarized light with the modest increase of the number of layers, and consequently the bandwidth and extinction ratio improves. When the number of layers is fixed, the centre wavelength is shifted to a shorter wavelength as the reference wavelength decreases.