For indoor visible light communication (VLC) systems aim to achieve communication and illumination simultaneously, the channel capacity are significantly affected by illumination demands in actual scenarios. To enhance the system performance, the wavelength division multiplex (WDM) technique can be introduced. In this letter, we analyzed the demands of illuminance and chromaticity’s influence on indoor WDM visible light communication system based on color light emitting diodes (LED). The spectra distribution, crosstalk and noise of WDM VLC system were analyzed and the relative optimal total channel capacity was obtained by optimizing the number of sub-channels and their intensity at standard illumination scenario. It’s shown that by applying WDM technique, the total channel capacity of LED based VLC system can be about 4 times than the situation of single sub-channel, even with indoor illumination constraints. What’s more, the system performance can be improved by adjusting appropriate number of sub-channels and their intensity accordingly.
Based on the complex movement of satellite platform, we take the impacts on spectral imaging by pitch, roll and yaw
into account. Then point spread matrix calculation principle is put forward, which takes transform the POS data into
point spread matrix. According to this theory, we proposed the concept of pseudo cross-correlation to set up the model of
spectral imaging degradation based on the pseudo cross-correlation, which combines the point spread matrix and original
spectral data by the concept of pseudo cross-correlation. And in this method, the process of spectral imaging degradation
is formed, which improve the existing problem of spectral imaging degradation based on the complex movement of
satellite platform. The simulation results show that this kind of degradation theory is suitable for solving the problem of
spectral imaging degradation based on the complex satellite platform movement completely.
Proc. SPIE. 9043, 2013 International Conference on Optical Instruments and Technology: Optoelectronic Devices and Optical Signal Processing
KEYWORDS: Signal to noise ratio, Detection and tracking algorithms, Scattering, Ultraviolet radiation, Computer simulations, Monte Carlo methods, Telecommunications, Antennas, Atmospheric turbulence, Non-line-of-sight propagation
Affected by atmospheric turbulence and multipath transmission, inter-symbol interference (ISI) is generated, and
communication speed is limited in the channel of non-line-of-sight ultraviolet (NLOS UV) communication. Thus, MIMO
space division multiplexing (MIMO-SDM) technology has a significant effect to reduce co-channel interference, fading
and improve the transmission rate. Combined with characteristics of UV channel and noise, model of UV
communication MIMO channel and channel capacity is developed, and the application of SDM technology based on
vertical bell laboratories layered space-time coding (V-BLAST) is investigated. Also bit error rate (BER) performances
with zero-forcing (ZF), minimum mean square error (MMSE) detection algorithm are obtained. Simulation results show
that the capacity of UV communication MIMO channel is related to the number of transmit and received antennas , and
channel SNR. And the BER performance with MMSE detection algorithm is better than ZF detection algorithm.
In this paper, the researches and experiments on the feasibility of a common aperture active imaging system using a
polarization beam splitter have been presented. The system includes a CCD imaging unit, a semiconductor laser unit, a
polarization beam splitter, a linear polarizer, a quarter-wave plate, a telescope objective, a designed laser collimating
lens and mechanical assembling structures. According to the analysis with Jones matrix, the system gains remarkably
high utilization ratio of luminous energy. Also, the system can reach an illuminating distance of 3km, a laser divergence
angle of 0.504° and a degree of uniformity of 83% theoretically. The experiments have been conducted to obtain images
of objects at 300m and 3km. From the results, clear illuminated objects can be identified and no impacts of back
scattering of atmosphere turbulence have been detected. However, to make this kind of systems more effective, higher
demands on the extinction ratio, reflectivity and transmissivity of the polarized components and the uniformity of the
illuminating spot should be met.
Since the absorption of ultraviolet radiation in the atmosphere is strong, it is difficult to image solar UV
radiation using ground-based telescopes. While, the moon which has no atmosphere and has stability
geological structure and low magnetic field, observing the sun on the moon is more suitable than observing
the sun on the earth. This paper describes the design of lunar-based solar telescope which can image the sun
in three wavelength: long-wave IR (8-12μm), visible (400-900nm) and UV(100-400nm). The telescope is
mainly composed of two parts: reflective telescope and splitting system. This design effectively avoids the
material restrictions of IR and UV imaging optical systems. The rationality of the optical system design of
the common aperture multi-wavelength telescope was proved by comparing the results with the images get
by single wavelength solar telescopes all over the world. Compared the images took under different weather,
the importance of the proposition of lunar-based devise is proved. Combined the splitters and the spectral
response range of detectors, the UV, visible and IR can be split and imaged by different detectors.
It is the astigmatism that leads the traditional imaging spectrometer based on Czerny-Turner to have low spatial
resolution. And it is discovered that when the distance between concave mirror and grating, x, is equal to the twice of
focal length, , of the mirror, SII = SIII = 0 and the aberration is the least as well as the astigmatism is eliminated greatly.
Meanwhile the toroidal mirror is presented to correct the astigmatism, and as well the aberration caused by the large
FOV is corrected by optimizing the surface tilt. Then both of the spatial and spectral resolutions are improved. Finally a
Czerny-Turner imaging spectrometer working in FUV (120 nm ~ 180 nm) with 2.5° FOV is designed, and its focal
length is 147.61 mm, its F number is 3.93. MTF of this imaging spectrometer is more than 0.39 at 20 lp/mm in the total
wavelength band of FOV, which satisfied the requirements of imaging spectrometer working on satellite in FUV.
The far ultraviolet scanning imaging spectrometer (FUSIS) is used to measure the composition and distribution of the
main molecules and atoms in the Earth's upper atmosphere. It is an important instrument in investigation of the physical
and chemical processes in the Earth's upper atmosphere. FUSIS works between 120nm to 180nm, its spectral resolution
is better than 1.0nm and its spatial resolution is 8 pixels. This paper describes a kind of ground calibration method and
facility of FUSIS. The FUV light is invisible, so all works must be done in high vacuum. The calibration facility includes
the FUV light source, collimator, and the vacuum chamber. The pumps of vacuum system can debase the pressure down
to 5×10-5Pa. Calibration experiments are accomplished in the vacuum chamber. The spectral calibration of FUSIS is
achieved with the linear interpolation method. The radiation transfer function is deduced. But some factors in the
function such as reflection components' reflectivity and detector's quantum efficiency are hard to test accurately. So we
use a radiation correction matrix instead of the transfer function in practice. Assuming the FUSIS instrument is a blackbox,
the matrix can be tested by experiments. FUSIS can get the absolute radiation intensity of target by calling the
Solar storms in the ionosphere have a great impact on human's life. It's of great significance to find an effective way for
an accurate prediction of solar storms. In this paper, we present a method based on GUVI FUV day-glow imaging data to
derive O/N2, an environmental parameter used to forecast Space Weather. In the retrieval, we selected two channels of
the FUV wavelengths, OI135.6nm and LBH2. In accordance with the linear relationship between O/N2 and 135.6/LBH,
we proposed 135.6/LBH to describe O/N2. With the method described in this paper, the data of a 4-day solar storm,
October 1 to 4, 2002, have been processed. Subsequently, the obtained O/N2 maps were in good agreement with previous
results. It demonstrated the retrieval process we put up is efficient.
In this paper, a new method is proposed for road extraction in complex environments. The algorithm takes full
advantages of the road image characteristics. Firstly, the image is preprocessed and the object edges are extracted. Then,
by dividing the image into many blocks (such as m×m), an improved Radon transform (RT) is performed to extract the
line segments in images. We do Radon transformation for each block. To reduce the computing time, a threshold is set
and images are resumed along the ribbon region of transformation domain. Experiments show that the presented method
can extract roads even in complex environments, and moreover, it can provide a complete description of the road.
When roads appear as irregular linear targets, most of traditional methods which use local information often give a false
alarm of linear feature. In order to overcome this disadvantage, we present an approach to extract main roads in aerial
images with oriented filters. Firstly, the leading gradient direction of the local areas is estimated. Then the image is
filtered along this direction. We use steerable filters to control the output and get the maximum output response along the
road direction. Based on the steps above, we make much improvement in details such as the determination for the size of
the sub-block image, the processing of image edge pixels and the processing of orientation angel areas and so on.
Experiments on remote sensing images of different environmental settings show that our proposed scheme achieves high
accuracy in the road extraction.
This article describes the characteristics of the far ultraviolet (FUV) radiation and its applications in the space weather's
research and prediction. The FUV imaging spectrometer is irreplaceable to get the FUV radiation data of the earth's
upper atmosphere. Some key technologies of FUV spectrometer are analyzed respectively, including window materials,
FUV light source, FUV detectors and FUV coating, which offer theoretical foundation for FUV imaging spectrometer.
The paper presents a FUV band imaging spectrometer's optical system which is based on crossed Czerny-Turner
structure with all reflective components in it. The wavelength range of the FUV spectrometer optical system is from
100nm to 200nm and the initial structure is simulated and optimized by Zemax in order to improve the spectral
resolution. The theoretical spectral resolution of the system is better than 1nm, and it has a certain imaging capacity.
This paper describes a design of sun-tracking warning demonstration system in solar blind UV. After analyzing of the
system structure and guide line of the sun-tracking warning system in solar blind UV, the key techniques of the
sun-tracking UV warning system are discussed and designed, including the optical system, UV filter module, optical
modulation system, UV detectors and its sun-tracking servo. A total reflect Cassegrain UV optical system with simple
structure, reliable performance and high-quality imaging ability is designed and manufactured. In order to enhance the
received SNR and process the signal easily, an optical UV filter and an optical modulation reticle are used to filter and
modulate the target's direct signals to alternating signal. Functional experiments show that sun-tracking warning system
needs better UV filter module whose total stopband rejection should be higher than 10-10.
A 2-D model is developed for the simulation. Calculations take into account the chemiluminence reaction of CO-O,
which is the dominant sources of radiation in the UV wavelength band considered, and particle emission/scattering
effects produced by alumina particles. The alumina particle is considered as a discrete phase through the continuous
flow, assumed to be in solid state with diameters ranging from 5 micron to 17 micron. The atmospheric effects, pressure
and temperature, are included in the boundary condition. Four cases, altitudes at 0km, 4km, 15km and 30km are
calculated separately, and comparisons are made with each other .Finally, the analysis of affecting factors is presented.
A practical single-scattering model of solar blind UV communication channel, which is suitable for NLOS digital
communication is presented in the paper. NLOS transmission loss of UV channel is deduced by Lambert law .
Calculation method of scattering phase function and integral of intersection volume between transmitting beam and
receiving beam are described detailed in prolate spheriodal coordinate. Base on them, a practicable calculation method
about signal to noise ratio (SNR) and bit error rate (BER) of UV communication systems is presented, which construct a
bridge between system parameters and digital system performances in simulation of UV communication channel and
systems .Under certain BER and typical modulations in UV communication , relationship between system parameters and
system performances are discussed.
The definition and classifications of the UV communication are described in the paper. The UV channel
consists of three sections: propagation loss section, scattering section and background-noise section. The
principle of selecting the wave band of UV communication is analyzed. The LOS and NLOS (a) transmission
models are presented, and the two configurations are well proved by outdoor experiments. The experiment
results also show that the communication distance of LOS can go up to 5kms, and NLOS(a) can reach 2kms
with the UV detectors at present.
A LOS solar blind UV communication channel model is presented in the paper, which consists of three sections: propagation loss section, scattering transmission section and background noise section. LOS transmission loss model of UV channel is deduced by Lambert law and noise power calculation is also analyzed. Base on them, a practicable calculation method of signal to noise ratio (SNR) is presented, which is a bridge between system parameters and system performances such as BER and limit communication distance in analysis of UV communication. Transmission loss and SNR of LOS are measured in outdoor experiments. The experiment shows that SNR calculation data agree with the experimental results quite well. The calculation also shows that the limit communication distance of LOS can achieve 7kms with the UV sensor at present.
2.1μm solid state laser operating at room temperature is a very useful laser source for optical communication, medical care, air pollution monitoring and Lidar, etc. It is eye-safe. It is also a very ideal pump source for optic parametric oscillator to get 3μm -5μm radiation. In order to further explore its potential applications, higher peak power and shorter pulse width are very desirable. Q-switching the laser is a most practical way to realize those goals. Among the most common used Q-switching techniques, mechanical Q-switching is not preferred due to that it involves use of a rotating motor, which has lower life time and causes undesirable vibration. E-O Q-switch material in this wavelength range is very expensive and quite susceptible to optical damage. On the other hand, low OH concentration quartz material exhibits very low absorption at the 2.1μm. The Cr:Tm:Ho:YAG 2.1μm laser has undesirable lower gain from the laser efficiency point of view, but offers a feasibility of using the A-O device for the Q-switching even the laser is pulse pumped. The Cr:Tm:Ho:YAG 2.1μm laser is a so called quasi-three level laser, which is characterized as having a higher threshold and lower gain. This study is focused on the optimization of the laser resonator design and the A-O Q-switch design for a higher laser peak power and shorter pulse width. Factors considered in the study include AO Q-switch’s RF frequency, modulation depth, active aperture, resonator length, resonator loss and pumping design, etc. Experiment results are compared with the Q-switched quasi-three level laser model. Final result of the Q-switched 2.1μm laser after preliminary optimization will be presented.