Honghui Jia

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.

The nonlinear optical properties of coupling and decoupling graphene layers

Third-order optical nonlinearities of graphene from monolayer to multilayers were investigated in the femtosecond regime, and the contribution of interlayer coupling to the nonlinearities was studied. The nonlinear refractive index γ of the order of 10−9 cm2/W and the nonlinear absorption coefficient β of 10−6 cm/W were obtained. By systematically investigating the nonlinear optical properties with the number of layers and comparing the coupling graphene with the decoupling superimposed graphene, we found that the coupling of interlayers has large effect upon the nonlinear refraction. These results provide an effective approach for developing graphene-based nonlinear photonic devices.

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.

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.

Detection of TNT in acetone using Raman spectroscopic signature

The detection of explosive agents is becoming more important and receiving much greater emphasis for homeland defense. Raman spectroscopy is a well established tool for vibration spectroscopic analysis and can be applied to the field of explosives identification and detection. The major bands of the Raman spectroscopy of industrial TNT (Trinitrotoluene, CH3C6H2(NO2)3) are analyzed and seven prominent peaks, that is 1616.9cm-1 (C=C aromatic stretching vibration), 1533.9cm-1 (NO2 asymmetric stretching vibration), 1360.1cm-1 (NO2 symmetric stretching vibration ), 1210.5cm-1 (C6H2-C vibration), 822.9cm-1 (nitro-group scissoring mode), 792.3cm-1 (C-H out-of-plane bend), and 326.7cm-1 (framework distortion mode) are used to identify the TNT. The Raman spectroscopes of TNT solved in acetone at different mass ratios are studied, and the TNT in the solution can be detected correctly according the relative distance, intensity, and peak area of the seven peaks. The TNT prominent peaks appear clearly in high level solution (the mass ration of TNT and acetone is more than 1:10). With the decrease of TNT concentration in solution, the signature of TNT becomes more and more weak. The low detection limit of TNT is limited by the noise of the instrument (NXR FT-Raman accessory module with Nicolet 5700 FT-IR spectrometer is used for our experiments. The low detection limit in our experiments is mass ratio 1:200, which is about 4mg/mL). The prominent peak heights are discussed in consideration of the TNT concentration. Taking one of the acetones peaks (1716.9cm-1) as the internal standard line, the relative height of the prominent TNT peaks is almost proportional to the concentration of the TNT in the solution. A fitting curve for the relations of prominent peak height according to the concentration is proposed with multinomial fitting method, which can be used to analyze the concentration of TNT more accurately.

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.

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.

Compound parabolic concentrator applied as receiving antenna in scattering optical communication

The two-dimensional (2D) compound parabolic concentrators (CPC) characteristics are analyzed. It is shown that CPCs height is taller and its light collecting ability is stronger with the CPCs field of view decreasing when the bottom radius is unchanged. According to the ZEMAX analysis, CPC is good at collecting optical signal, and the antenna combining CPC with hemispherical lens can gather more optical signal than a single CPC or CPCs combined in series. The light propagation of scattering optical communication based on multiple scattering is simulated by Monte Carlo method, and the results show that using CPC as receiving antenna can strengthen communication systems signal collecting ability and increase its communication distance.

Study and design on high-data-rate UV communication system

Ultraviolet communication is a new means of free space optical communication links developed since 1990s. In the paper, we first point out the low data rate drawback of the UV communication system using mercury lamp, and find the limitation arises because of the self trapping of the mercury atomic resonance radiation. Then the working principle and the max modulation speed o f the high data rate UV communication system are explained, at last the high date rate UV communication system which based on the low pressure iodine lamp is described in details. The high UV communication system includes an emitter, a receiver and light propagation channel. The light propagation channel is in the low air. Finally, the system has accomplished good voice and high data rate communication in short distance and its maximal communication rate is 48Kbps which decuple the data rate of the UV communication system made by GTE in 2000. Because of shorter wavelength of the iodine UV source, the whole communication system is more suitable for the security communication usage.

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.