The simulation can evaluate the performance of the optical system and provide guidance for its improvement. At present, most of the research on imaging modeling of hyperspectral system is based on modulation transfer function method. However, this method has its limitations. Therefore, this paper proposes a reliable method for imaging modeling of hyperspectral optical system based on ray tracing: (1) In the spatial dimension, the vignetting coefficients corresponding to the image sampling points are obtained by ZEMAX, and the diffuse spots model of optical system is obtained by tracing the position of the light on the image plane which emitted by the object points after passing through the mesh points on the pupil surface. (2) In the spectral dimension, the spectral lines on the detector are obtained by non-sequential ray tracing, and separate the spectral lines of different wavelengths. The spectral bending coefficient and spectral distortion coefficient can be obtained by least square fitting. In this paper, high spatial and high spectral resolution images served as input sources for imaging simulation. By changing the grating constants, band range, defocusing quantity of the optical system and length of the slit, the changing trends of the output images in radiation intensity, spatial correlation, spectral characteristic curves and vignetting curves are analyzed, and the reliability of the model is verified.
Atmospheric radiation transmission is one of the most complex and variable parts of hyperspectral remote sensing systems. Aimed at the abstraction and complexity of the influence of atmospheric radiation on the quality of hyperspectral imaging, the design of simulation software for hyperspectral atmospheric radiation transmission imaging in visible light is proposed. Firstly,this paper analyzes the radiation transmission process including the surface reflectivity, the adjacent pixel reflectivity and the atmospheric transmission factor, and describes the calculation method of the radiance at-sensor for the hyperspectral image in the visible light bands. Then the multi-core CPU based on the .Net environment is constructed. The adjacent pixel point diffusion function parallel computing module and the GPU-based on-satellite reflectivity parallel computing module; the experimental part takes the hyperspectral surface reflectance image as input data, and degenerates the output into the hyperspectral radiance simulation data in different scenarios. At the same time, test of the time of individual modules and the overall algorithm in the simulation process is tested. The experimental results of real-time performance show that the parallel algorithm has significantly improved.
A prism compressor can compensate dispersion of femtosecond light pulses travelling in air for laser ranging. An
accurate expression of the group delay dispersion (GDD) of a prism compressor at arbitrary incident angle and at arbitrary
incident point is obtained, which is of benefit to finely compensating dispersion of femtosecond pulses. Influences of
several parameters on group delay dispersion are analyzed for the active compensation of dispersion of femtosecond
pulses. These expressions are convenient to applications of intra- and extra-cavity dispersion compensation of ultra-short
laser pulses, as well as fine compensation of satellite laser ranging and laser altimetry.
Optical receiving antenna is usually positioned before the detector of an indoor visible light communication (VLC) system in order to collect more optical energy into the detector. Besides optical gain of the antenna, the field of view (FOV) plays also an important role to the performance of a VLC system. In this paper, the signal noise ratio (SNR) and inter-symbol interference (ISI) versus FOV of the antenna are simulated via Line-of-Sight (LOS) and non-Line-of-Sight (NLOS) links within a room with a size of 5m × 5m × 3m. Results show that, the blind area appears while the FOV is less than 40 deg. and the SNR reduces as FOV increases and keeps small when FOV is more than 70 deg.. Furthermore, the average power of ISI rises with the increase of FOV, and the rising trend is relatively moderate when FOV is below 50 deg., while there is a rapid increase between 50 deg. and 70 deg. and finally tends to be stable after 70 deg. Therefore, it is practical to determine the FOV of the optical receiving antenna in the scope of 40 to 50 deg. based on the installment of LED lights on the ceiling here so as to avoid the blind area, attain high SNR, and reduce the influence of ISI. It is also worthwhile in practice to provide an identifiable evidence for the determination of FOV of the optical antenna.
This article gives an overview of airborne LIDAR (laser light detection and ranging) system and its application. By
analyzing the transmission and reception process of laser signal, the article constructs a model of echo signal of the
LIDAR system, and gives some basic formulas which make up the relationship of signal-to-noise ratio, for example, the
received power, the dark noise power and so on. And this article carefully studies and analyzes the impact of some
important parameters in the equation on the signal-to-noise ratio, such as the atmospheric transmittance coefficient, the
work distance. And the matlab software is used to simulate the detection environment, and obtains a series values of
signal-to-noise (SNR) ratio under different circumstances such as sunny day, cloudy day, day, night. And the figures
which describe how the SNR of LIDAR system is influenced by the critical factors are shown in the article. Finally
according to the series values of signal-to-noise ratio and the figures, the SNR of LIDAR system decreases as the
distance increases, and the atmospheric transmittance coefficient caused by bad weather, and also high work temperature
drops the SNR. Depending on these conclusions, the LIDAR system will work even better.
After giving the detection principle and geometric model of airborne scanning lidar briefly, this paper analyzed the
existent error sources in detection process, and established the correction equation of position error. The simplified
models of the attitude changes and aircraft oscillation in frequency are developed. Based on computer simulation of their
simplified models, the outcome of simulation is analyzed. Finally a few elementary conclusions are obtained and some
suggestions are offered for improving detection accuracy and for error compensation of airborne scanning lidar data. The
results are of reference value in research on the improvement of detection accuracy of airborne scanning lidar.
A wedge-shaped probe is developed and applied for the detection of transient electrical signals in an ultrafast scanning
tunneling microscope measurement system. The probe is composed of a low- temperature grown GaAs photoconductive
switch and a metal tip with a diameter of 5 micrometers. The designed probe functions as a sampler of transient signals
generated by a sample of coplanar strip photoconductive switch with ultrafast optical pulses of 100 fs in the ultrafast
measurement system. The shape of the probe makes the approach of the probe to the sample in a way that is much easier
than the traditional rectangular one. The metal tip is attached to the coplanar strip transmission line integrated in the
photoconductive switch. The design of the probe is presented and its performances have been reported in this paper.
Photo of the wedge-shaped probe is given and transient signals in picoseconds were observed in contact mode with the
developed wedge-shaped probe.
Monte Carlo simulation method has been used to study the linear mode of photoconductive semiconductor switches
(PCSS). Its triggered source is a femtosecond laser pulse. The simulation results are well in agreement with experiment
data, so the model is accurate. Based on the model, some important factors which influence the response time of PCSS
have been analyzed by computer simulation. Then the sizes of these parameters that make an important contribution to
get better response time have been deduced. From this simulation analysis, it is sure that some experiment conditions can
be used more enough. In other words, the response time can be further shortened under the same experiment condition.
Moreover, the transition from linear mode to non-linear mode has been analyzed using this model.
This paper studies a distributed fiber optic perturbation locating sensor used for security system, which is based on dual
Mach-Zehnder interferometers. This system consists of two Mach-Zehnder interferometers with the common sensing arm,
reference arm, two couplers and one laser source. This kind of distributed fiber optic perturbation locating sensor is very
suitable for the measurement of the phase shift induced by some perturbation such as strain and vibration. When
perturbation exerts on the sensing arm, a time delay will generate between the two output signals of the dual Mach-Zehnder
interferometers. From the time delay, the location of the perturbation can be obtained. Experimenting on the type
disturbance's optic cable and forcing on the 18.46km long distance fiber, the system correctly shows the position for real
time and the average error is 390m. The experiment shows that the system can be applicable for locating on 40km distance
fiber cable when the power of the laser resource increases to 300μW.
An eye-safe, coherent Doppler Light Detection and Ranging (CDL) system for speed measurement under development at
BUAA's School of Instrument Science and Opto-electronics Engineering is introduced in this paper. It consists of a
1.55-μm Er-doped fiber laser transmitter, a monostatic optical antenna, a single-mode fiber (SMF) interferometer, an
InGaAs photodiode detector, and signal processing equipments. All devices of optical circuit are connected by SMFs
making the system reliable and setup arrangement flexible. The goal is to give the evaluations of the Doppler frequency
shift and platform speed. Since the speed accuracy is time-independent, the CDL system can be used for integrated
navigation system. The quality of Doppler-shift estimation by a spectrum analysis technique, fast Fourier transform (FFT)
algorithms, ameliorates as the signal-to-noise ratio (SNR) increases. For the developed CDL system incorporating with
SMF interferometer, only the light beam of mode LP01 is permitted to propagate, therefore the SNR is improved greatly.
Experiments were performed on a moving hard target with the CDL system and the results were presented.
The design and field test of a perimeter security system based on fiber optic disturbance sensor was described. The
system consisted of fiber optic disturbance sensor and control computer. The fiber optic disturbance sensor was in Mach-Zehnder interferometer configuration using single mode fiber cable, which made the system relatively low cost. A digital
Phase Generated Carrier (PGC) demodulation technique was used to eliminate phase drifts in the interferometric sensor.
The demodulator was based on Field Programmable Gate Array(FPGA) and Digital Signal Processor(DSP). A prototype
system with 1Km sensing cable was constructed and tested. The sensing cable was bound on the fence to detect
disturbance generated by intruder. The test result verified that this sensor was sensitive to intrusion behavior. Typical
disturbance signal was recorded when intrusion behavior was going on. There was obvious characteristic in the recorded
signal. Intrusion behavior generated non-stable random signal, which had many amplitude peaks. And the frequency was
below 500Hz. This was helpful for recognition algorithms development. Wind in the test field also generated low
frequency background noise and increased recognizing difficulties.
Ultrafast measurement system for transient electrical signals using a scanning tunneling microscope has been developed. The key of the system is a probe integrated with a low-temperature grown GaAs photoconductive switch that is used as a sampler of transient signals generated by ultrashort laser pulses with another photoconductive switch. The tunneling tip is attached to a coplanar strip transmission line with an integrated photoconductive switch. The probe fabrication process and tip characteristics have been reported here. A topographic STM image scanned with such a probe on a gold sample on Si substrate is given. A transient signal with 1.2 ps pulse width in tunneling mode and 2.0 ps in contact mode were observed with the probe.
We present experimental results of time-resolved signals of photoconductive (PC) switches with an ultrafast scanning tunneling microscope, which combines ultrashort laser techniques with scanning tunneling microscope (STM) to obtain simultaneous high temporal and spatial resolution. The picosecond electrical transients were generated by optically exciting the photoconductive switch between a high-speed coplanar strip transmission lines. The measured PC switch demonstrated a linear relation between the amplitudes of the time-resolved pulse signals and the photoconductive currents as well as a linear relation between the amplitudes ofthe signals and the bias voltage applied to the PC switch. The resolved transient signal in contact mode showed a FWHM of 3.2 ps, and the transient signals in non-contact mode were from the capacitive coupling between the tip and the coplanar transmission line.
In this paper we introduce an ultrafast photoconductive (PC) switch made from low-temperature-grown GaAs, which was fabricated for the generation and detection of electric transients in an ultrafast scanning tunneling microscope (USTM) system. The PC switch was manufactured on a quartz glass substrate. This transparent substrate allows illumination ranging from the front side to the backside. The use of quartz glass as the substrate enables also the low loss of the transmission of frequencies up to the THz regime. A coplanar strip line (CPS) was integrated on the PC switch, in order to propagate THz pulse on the transmission line. For a CPS with width and spacing of 10 micrometer and the PC switch with width of 50 micrometer, the dark current between the two electrodes is about 0.1 pA with a switch voltage at 10 V. The obtained PC switch showed linear I-P, I-V characteristics, low noise, high sensitivity, low dark current, and low background current. The USTM measurements show also a full width at half maximum (FWHM) pulse width of 1.3 ps.