Proc. SPIE. 9233, International Symposium on Photonics and Optoelectronics 2014
KEYWORDS: Polarization, Modulators, Free space optical communications, Optical communications, Data communications, Transmitters, Telecommunications, Defense technologies, Free space optics, Refractive index
Retroreflective free-space optical communication is a new method of optical communication, it is achieved by using a multiple-quantum-well (MQW) modulator as a passive data transmitter. This work analyzes the polarization propagation of light in the MQW modulator, and the corresponding influence to a retroreflective link. Results show that, on the condition that the intensity and incident angle of the incident light remains to be constant, the polarization and intensity of the transmitted light varies markedly; if the polarization of the incident light is carefully considered for a specific MQW modulator, the retroreflective signals can be improved for a retroreflective free-space optical communication link.
With low radiation background of solar-blind UV and strong scattering of UV photons by atmospheric particles, UV
communication can be made use of to set up a non-line-of-sight (NLOS) free-space optical communication link. Polarization modulation, besides the traditional intensity modulation, is presented to enhance the data rate of the UV
communication system. The configuration and the working process of the dually modulated UV communication system
with intensity modulation and polarization, the theoretical evaluation of polarization modulation, and a numerical of the scattering matrix are presented, with the conclusion that polarization modulation is achievable. By adding the polarizing devices and changing the coding procedures, the existing singly-modulated UV communication systems with intensity modulation are easily modified to be dually-modulated ones with polarization modulation and intensity modulation. Ideally speaking, the data rate of the dually-modulated UV communication system is the product of the data rate of the singly modulated system and the number of polarization modulation.
The UV radiance of the missile plume is considered as gray body radiance, and transmission efficiency and backgroud
radiation of UV in atmosphere are obtained by Lowtran 7. The signal-to-noise ratios of missile plume UV radiation at
different altitudes are estimated seperately for the ground-based, air-based and space-based systems of missile precaution, results show that, the SNR of the ground-based system decreases, the SNR of the air-based system firstly increases and then decreases, and the SNR of the space-based system increases with the growth of the altitude of missile; The SNRs of the ground-based and air-based systems are both relatively large aroud 300nm while the SNR of the space-based system is relatively large at the band from 250nm to 290nm; The SNR of the ground-based reaches the maximum when the altitude of missile is below 5km , the SNR of the air-based system is at the maximum between 10km and 20km, and the SNR of the space–based system is at the maximum above 40km. The results can be applied to designing the integrated system of missile precaution from air to space.
Rugate coatings are usually defined as optical coatings that present a continuous variation of refractive index in the
direction perpendicular to the film plane. Such kind of optical coating has optical and mechanical properties that differ
from those of conventional high-low-index stacks. Especially, the broad angle range and the low optical scatter level
make them superior to traditional stacks. Antireflective (AR) coatings have found increasing applications. In this paper,
the principal aspects of rugate coatings theory are discussed and the emphasis is focused on polarization effect of the
incident light. The reason accounting for difference of the transmissivity was analyzed in the case of polarization and
board angle incidence. To eliminate polarization effect, a method of designing antireflection coatings using rugate
coatings was demonstrated. Antireflection coatings for the ultraviolet spectral region in the wavelength range 300-400
nm and incidence angle from 0 to 80 degree were designed. Then the implementation of optimization recurred to optimac
and conjugate gradient. It shows that the result of optimization is ideal. For AR coatings, this design method can enhance
the ratio of utilization of optical energy.
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, CH<sub>3</sub>C<sub>6</sub>H<sub>2</sub>(NO<sub>2</sub>)<sub>3</sub>) are analyzed and seven prominent peaks, that is 1616.9cm<sup>-1</sup> (C=C aromatic
stretching vibration), 1533.9cm<sup>-1</sup> (NO<sub>2</sub> asymmetric stretching vibration), 1360.1cm<sup>-1</sup> (NO<sub>2</sub> symmetric stretching
vibration ), 1210.5cm<sup>-1</sup> (C<sub>6</sub>H<sub>2</sub>-C vibration), 822.9cm<sup>-1</sup> (nitro-group scissoring mode), 792.3cm<sup>-1</sup> (C-H out-of-plane bend),
and 326.7cm<sup>-1</sup> (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 acetone's peaks (1716.9cm<sup>-1</sup>) 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.
In the paper, The importance of research in non-line-of sight(NLOS) ultraviolet(UV) propagation channel is first pointed
out, and then an experimental system based on Lock-In-Amplifier (LIA) technology is set up to explore the NLOS UV
propagation channel characteristics in the atmosphere, and the related experimental results are good helpful to design and
evaluate the NLOS UV communication system. The research results show that: firstly, the received energy decreases
much quickly with the distance enlarged, and it is also influenced by the emitting elevation angle and emitting field of
view angle; secondly, the visibility, wind force, rain rate and fog has little influence on the received power in the short
working distance, but with the propagation distance is getting longer, the fog play an very important role on the received
signal; finally, some effective methods to enlarge UV communication system distance are discussed, such as UV source
power, received antenna diameter and UV detector quality, and experimental data show that the best way to improve
UV communication system is to improve the detector sensitivity.
Model of non-line-of-sight (NLOS) UV transmission was introduced, NLOS UV transmission was simulated using
Monte-Carlo method. Impact of visibility, rainfall, wind speed, light source radiation power, detector sensitivity on
transmission range was debated. Results showed that visibility and rainfall had relative impact on transmission range,
while wind speed hardly had any influence, it was a main way to improve range by enhancing detector sensitivity, and it
weren't very effective to increase source radiation power.
Ultraviolet communication is a new means of free space optical communication links developed since 1990's. 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.