We demonstrate femtosecond pulses evolution in silicon photonic nano-wire waveguides with generalized nonlinear
Schrödinger equation modeling along with auxiliary carrier dynamics. The temporal and spectral properties of the output
pulses are simulated with increasing input pulse energies, and high-order soliton pulse compression and splitting, along
with spectral broadening and red-shift are observed remarkably. The impacts of high-order nonlinear effects, including
the self-steepening and intrapulse Raman scattering on the pulse evolution are analyzed, and it indicates that the IRC
results in noticeable temporal tailing edge tilting and spectral red-shift, while the impact of the self-steeping can be
negligible. The contributions of the third order dispersion and various nonlinear effects on the pulse properties are
detailedly investigated to better understand the femtosecond pulses propagation, in support of further chip-scale optical
interconnects and signal processing.
Opto-electronic hybrid correlator can realize the combination of electronic flexibility and high speed of optical
computing, so it has widely potential applications in high speed optical information processing system, especially
recognition and tracking system. But the opto-electronic conversion speed and the positioning accuracy of correlation
peak constrains the performance of this system. This paper first proposes an idea that PSD(Position Sensitive Device)
can be applied in optical correlation peak detection instead of traditional CMOS/CCD sensor. It is displayed by
theoretical analysis that this system can attain a correlation calculation speed of 20,000 frames per second, which
indicates that the system can satisfy high speed demands of target recognition and tracking. Through optimal design of
Fourier lens, the size, shape and intensity of the correlation peak spot have been optimized to satisfy the positioning
accuracy requirement of PSD. The property of PSD can lead to nonlinear displacement error of the correlation peak and
this paper use a linear line to fit the experimental outcome. Besides, this paper introduce the definition positioning
accuracy, which is defined the maximum deviation apart from fitting linear outcome. The positioning accuracy of the
novel opto-electronic hybrid correlator is calculated approximate 10 pixels (0.04mm), which is small enough to satisfy
the demand of recognizing and tracking a target. In conclusion, a high speed and high accuracy recognition and tracking
system has been realized based on the opto-electronic hybrid correlator.
With both ultrafast optical properties of femtosecond pulse and cylindrically symmetric polarization properties of
radially polarized light, the radially polarized femtosecond pulse beam has significant applications in super-high density
optical storage and ultra-intense lasers. A scheme for generating radially polarized femtosecond pulse beam by a
polarization plates array is proposed, in which a phase-only liquid crystal spatial light modulator (LC-SLM) is used to
load different phase retardation distribution in transverse into linearly polarized femtosecond pulse beam. Associated
with a quarter wave plate, the input linearly polarized femtosecond pulse beam will be converted to radially polarized
femtosecond pulse beam at the back of the polarization plates array. The experimental results indicate that the scheme
can be well used to generate radially polarized light, and more effective results can be obtained with the increase of
sectored polarization plates.
Grid algorithm is a classical star identification algorithm based on star pattern. A three-dimensional grid algorithm for
all-sky autonomous star identification is proposed, which is associated with the information of star view magnitude. In
contrast with traditional grid algorithm that constructs the grid cells on two-dimensional plane (e.g. x-y coordinate plane),
the proposed approach makes use of the star view magnitudes of the neighboring stars as the third dimension (e.g. z-axis).
A pattern is generated for each of its three-dimensional grid cells that contain neighboring star are 1, and those without
are 0. The progress of star identification is to determine which pattern in the database is associated with the particular
sensor pattern. Simulation shows that this method can achieve identification rate of 98.0% while the standard deviation
of star position error and star view magnitudes are 1 pixel and 0.3Mv respectively. Compared with the traditional grid
algorithm, the identification rate is higher, and the average runtime is 50 percent shorter.
We have developed a calibration approach for a star tracker camera. A modified version of the least-squares iteration algorithm combining Kalman filter is put forward, which allows for autonomous on-orbit calibration of the star tracker camera even with nonlinear camera distortions. In the calibration approach, the optimal principal point and focal length are achieved at first via the modified algorithm, and then the high-order focal-plane distortions are estimated using the solution of the first step. To validate this proposed calibration approach, the real star catalog and synthetic attitude data are adopted to test its performance. The test results have demonstrated the proposed approach performs well in terms of accuracy, robustness, and performance. It can satisfy the autonomous on-orbit calibration of the star tracker camera.
We construct an all-optical nonlinear joint transform correlator utilizing the rewritable photochromic diarylethene film, which serves as a joint transform power spectrum recorder. The computer simulations indicate that, with the nonlinear response characteristic of the diarylethene film, the SNR and peak sharpness of the correlator can be improved. A compact correlator prototype with a 5-cm focal length is constructed and the experiment results verify that the physical length can be reduced remarkably owing to the high resolution of the diarylethene film.
An autonomous star tracker is an opto-electronic instrument used to provide the absolute three-axis attitude of a spacecraft utilizing star observations. The precise calibration of the measurement model is crucial, as the performance of the star tracker is highly dependent on the star camera parameters. We focus on proposing a simple and available calibration approach for a star tracker with wide field of view. The star tracker measurement model is described, and a novel approach for laboratory calibration is put forward. This approach is based on a collimator, a two-dimensional adjustable plane mirror, and other ordinary instruments. The calibration procedure consists of two steps: (1) the principal point is estimated using autocollimation adjustment; and (2) the other camera parameters, mainly the principal distance and distortions, are estimated via least-squares iteration, taking into account the extrinsic parameters. To validate this proposed calibration method, simulations with synthetic data are used to quantify its performance considering the errors of the distortion model and calibration data. The theoretical analysis and simulation results indicate that the uncertainties of the measured star direction vectors are less than 4.0×10−5 rad after calibration, and this can be further improved.
With excellent physical properties the photorefractive crystals, such as BSO (Bi12SiO20), BaTiO3 and GaAs materials, have, can be widely used in optical correlator to implement auto pattern recognition. As the basic devices in optical
correlator, the properties of optically-addressed spatial light modulator are very important. By analyzing the dynamic
process of the BSO spatial light modulator, especially the changes of the read-out light while in writing under various
operation modes, the distinctness between various operation modes is summarize. Furthermore, considered with the
photo-induced current pulses, the method to optimize the BSO spatial light modulator is proposed. The BSO spatial light
modulator working in optimum operation mode is used to design a optical correlator to implement auto pattern
recognition.
KEYWORDS: Gyroscopes, Space operations, Navigation systems, System integration, Sensors, Space telescopes, Star sensors, Optical testing, Reliability, Stars
In order to achieve continuous attitude information of the spacecrafts or the telescopes, the star-sensors and the gyros
are usually integrated to form navigation systems, which measure and determine the attitude-angles synthetically. The
space combinations of the measure-vectors of the star-sensors and the gyros are analyzed to find out the influences of the
combination modes on the determination precision of the attitude-angles, and the influence trends are summarized.
Furthermore, the optimum space combinations of the measure-vectors are proposed for improvement the determination
precision of the attitude-angles and the redundancy/complement of star-sensors and gyros. The optimum space
combinations of the measure-vectors are benefit for designing optimum integrated star/gyro systems to achieve high
determination precision of the attitude-angles, even any of the star-sensors or the gyros works with poor measurement
precision, so as to improve the reliability of the navigation systems.
Optical correlation manipulation presents great potential in future machine vision systems, which
can be used in a large variety of application fields. Nevertheless, how to extract the tracking signal
effectively and fast for the feedback system is still an open question. In the present paper, we present
novel target recognition and tracking approach in optical correlator system. The tracking signal is
extracted by using genetic algorithm. In this way, a photoelectric detector with short response time
can be employed in the system instead of digital camera, the tracking signal can be extracted by
iteratively evaluating the signal detected by the photoelectric detector until converge. Numerical
simulations were performed to validate the validity of the approach presented in the manuscript.
Along with the development of parallel optical computing, more and more two-dimensional optical modulating and
transforming devices with high response speed are needed. As the response times of most of the photorefractive crystals
are very short, optically addressed photorefractive BSO spatial light modulators are the most important devices which
have been successfully used in many two-dimensional optical information processing systems. However, the response
time is still too large for optical computing applications. In order to achieve adequate contrast ratio, a majority of the
operation process of the photorefractive spatial light modulators have to account for the accumulating of the
photoinduced charges so as to build up a strong internal electric field. The experiment results show that, the
photoinduced currents through the external circuits which provide the applied voltage behave with the characteristics of
pulses. The properties of the current pulses vary with the wavelength of the write-light, the direction of the external field,
the value of the applied voltage, the thickness of the BSO films and the properties of the external circuits. The analysis of
the photoinduced current pulses is useful for optimizing the structure, the operation modes and the performance of the
photorefractive spatial light modulators. Furthermore, the analysis can provide some useful information for choosing
appropriate materials and devices for optical computing applications, and building up efficient all-optical architecture for
the future parallel optical computers.
The applications of the joint transform correlator are partly limited by the information loss of the power spectra while
being detected and transmitted by conventional detectors and electrically addressed spatial light modulators. The
re-writable diarylethene films, which used to be mainly used in optical storage, are successfully tried to detect and
transmit the power spectra of the joint transform correlator instead of the CCDs and the electrically addressed spatial
light modulators. According to the experiment results and the corresponding comparisons and discussions, the
re-writable diarylethene films can be used to detect and transmit the power spectra of the joint transform correlator
better than the CCDs and the electrically addressed spatial light modulators in the case of decreasing the information
loss. With high resolution and large dynamic range, besides optical storage, the re-writable diarylethene films will be
widely used in optically addressed spatial light modulators if the operation period can be shortened remarkably.
Optical digital processor is the core of some future optical parallel computing systems. A novel optical discrete
correlation processor using a high-speed digital micromirror device is proposed, which mainly consists of a VanderLugt
correlator. In the processor, the computer generated hologram filters which are inputted by the digital micromirror device
will determine the specific logical operations. With properties of high reflectivity, high resolution and short response
time, the digital micromirror device can control the wave-front of the light beams with high optical efficiency, large
contrast ratio and high rate. An experimental prototype is constructed to demonstrate some specific logical operations.
The experiment results indicate that, the novel optical digital processor based on digital micromirror device can perform
some specific logical operations properly, and the digital micromirror device can remarkably improve the performance of
the optical digital processor.
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