Conventional imaging systems for correction of geometric and chromatic aberrations often use two dozen individual optical elements. In recent years, researchers have introduced computational imaging to this situation. By relaxing constraints on the front-end optical system and using algorithms for restoration on the image side it can achieve high-quality imaging. In this paper,we used single DOE (diffractive optical element) and CIT (computational imaging technology) to achieve clear imaging in the visible-band from 400nm to 700nm. In optical design, PSF (point spread function) with wavelength consistency are obtained by coding the structure height of the DOE. In image recovery, the characteristics of a large diameter of PSF proposes a multi-scale deconvolution restoration algorithm. The deconvolution smooth noise is used to the low scale, and then recover the original size to achieve image restoration. The simulation shows that the frequency of the traditional phase Fresnel diffraction lens in this band when the MTF at 0.1 is only 2.58p/mm, while this method can achieve 110p/mm under the same condition. The results prove that DOE based on computational imaging can achieve visible-band achromatic and clear imaging effects maintaining a thin and light physical structure.
In our study, a communication experiment with a 13-km horizontal urban link was conducted based on space diversity technology to examine the communication performance and scintillation effect of this link. Four different distribution models, including the Gamma–Gamma distribution model, were selected. Although the scope of application of the other distribution models was smaller than that of the Gamma–Gamma distribution model, they had better fitting effects than the Gamma–Gamma distribution model did regarding the use of space diversity technology in extreme urban environments with strong or weak turbulence; the degree of fit could reach more than 0.9. We concluded that the space diversity technology had a certain influence on the probability density function of the light intensity fluctuation and a significant inhibitory effect on the scintillation light intensity, resulting in a gain of more than an order of magnitude for the bit error rate.
A non-mechanical photoelectric tracking technology based on liquid crystal phased array was proposed. A mathematical model of a liquid crystal phased array photoelectric tracking closed-loop system was established. The laser emits incident light of a specified wavelength. Incident light enters the liquid crystal phased array through polarizers, waveplates and other optical devices. The difference between the deflected beam and the incident light is received with the camera after the liquid crystal phased array. The liquid crystal phased array adopts voltage control to achieve the deflection of the incident beam and achieve the purpose of accurate tracking. The motion state of the simulated target is analyzed and a modern control algorithm is designed. Subsequent simulations and experiments were conducted. Simulation results show that the dynamic tracking error of the liquid crystal photoelectric tracking system is better than 18μrad. Its closed-loop bandwidth exceeds 2.3HZ. On the basis of the above work, a desktop demonstration experiment platform was built. Experimental results show that the dynamic tracking error of the liquid crystal tracking control system is better than 20μrad, which has good robustness.
High-precision, stable tracking technology on a mobile platform is a key technology for realizing the integration of airborne search and tracking. In this study, coarse-fine compound technology based on gyrostabilization and miss tracking is applied. First, the working principle of the coarse and fine composite system is analyzed, and then the coarse and fine composite algorithm is modeled. Thereafter, the error of the coarse and fine composite axis is analyzed, and the precision tracking servo control algorithm is designed. Finally, using the model and algorithm designed to control the single reflector and galvanometer, the coarse tracking of the space target and the fine tracking of the source are completed under the condition that the equivalent sine amplitude is 5 deg and the frequency is 0.2 Hz. At the same time, a test system was built for performance verification. The algorithm achieved a coarse-tracking azimuth-axis tracking accuracy [root mean square (RMS)] of 26.3 μrad and a pitch-axis tracking accuracy (RMS) of 28.9 μrad. After composite tracking was switched on, precision tracking azimuth-axis tracking accuracy (RMS) improved to 7.9 μrad and pitch-axis tracking accuracy (RMS) improved to 6.3 μrad, both better than 10 μrad. This study provides new insights into the stability and precision tracking of single cameras on airborne platforms. At the end of this work, the outdoor experiment to verify the influence of random interference on the system performance under given conditions and the subsequent optimization direction of the system are given.
Stable gaze scanning control technology is the key to realize the integration of stable imaging, search, and tracking on airborne platforms. We investigate the control technology of stable gaze scanning on an airborne platform. The working principle of a stable staring scanning system is analyzed, and a servo system control algorithm is modeled. The position loop, velocity loop, and acceleration loop are designed. A stability model of the space with inclination angle is established. The coordinate transformation relationship between inertial coordinate system and airborne axis coordinate system is obtained. The designed control model and algorithm are used to control the single-lens reflex mirror mounted at an angle of 15 deg for spatial gaze pointing and step scanning. A test system is built for performance verification. Results show that the root-mean-square accuracy of the proposed algorithm is higher than 10 μrad in a dynamic staring step scan with ±30 deg and a step length of 2.16 deg. The single-step time is <52 ms, the stabilization time is >53 ms, and the servo system overshoot is small. The system step accuracy root mean square is better than 52 μrad. These findings confirm the effectiveness of the integrated search and follow technology under an airborne platform.
We discuss the design of a digital laser communication receiver and its sensitivity test process. Laser communication is especially suitable for long-distance low-power micro–nano satellite links due to its narrow beam width, but the electro-optical noise situation of the micro–nano satellite platform is complicated and bad. Hence, it is necessary to introduce a digital laser communication receiver to flexibly suppress interference and noise to improve communication sensitivity. A digital laser communication receiver based on the avalanche photodiode (APD) is designed. Based on the principle of digital communication error probability, a high-sensitivity APD device is selected, and a digital receiving channel based on field programmable gate array is designed. The finite impulse response, the dynamic threshold, the baseband median, and other filtering algorithms are used to optimize the signal-to-noise ratio and enhance the detection sensitivity. At the same time, an 800-nm laser communication receiver sensitivity test experimental architecture is designed and the detection sensitivity experiment is carried out. The experiment indicates that the APD receiver achieves detection sensitivity at an Mbps rate better than −60 dBm. The digital filtering algorithm provides a filtering signal-to-noise ratio improvement of about 15 dB, which supplies a reference for the receiver design of micro–nano satellite laser communication.
The size of the field of uncertainty (FOU) is an important performance indicator of spatial optical communication systems and is closely related to the line-of-sight (LOS) pointing accuracy. Considering the aircraft-ground laser communication as the research background, the initial pointing angle of the LOS of communication is obtained using the coordinate transformation matrix, and the factors that affect the LOS pointing accuracy error are analyzed. The Kalman filtering technique is introduced into the LOS pointing system to complete system modeling and simulation analysis. The simulation results show that the position, attitude angle, and other data fluctuations of global positioning system/inertial navigation system composite systems can be smoothed effectively by adding a Kalman filter to the LOS pointing system, and the prediction function of the filter can reduce the influence of dynamic lag. The proposed approach improves the accuracy of the LOS pointing, reduces the size of the FOU, and provides reference and guidance for the design of space optical communication systems.
Demanding for the closed communication among urban buildings, a solution for close range laser communication is proposed. The functional composition of the system is demonstrated and analyzed and the parameters of the system are reasonably allocated. The system design is used with independent optical aperture. The energy model under the inherent error of transceiver is analyzed and calculated. On the basis, the actual communication test was carried out, the specific test operation process is given and the measured data are obtained. The deviation between the average data and the theory is not more than 0.58dB. The correctness of the theoretical energy model is verified. The energy model can be used to guide the design of remote distance communication terminal. At the same time, the successfully development and communication test can be effectively accelerated the application of civil communication for urban buildings.
In space optical communications, it is important to obtain the most efficient performance of line of sight (LOS) pointing system. The errors of position (latitude, longitude, and altitude), attitude angles (pitch, yaw, and roll), and installation angle among a different coordinates system are usually ineluctable when assembling and running an aircraft optical communication terminal. These errors would lead to pointing errors and make it difficult for the LOS system to point to its terminal to establish a communication link. The LOS pointing technology of an aircraft optical communication system has been researched using a transformation matrix between the coordinate systems of two aircraft terminals. A method of LOS calibration has been proposed to reduce the pointing error. In a flight test, a successful 144-km link was established between two aircrafts. The position and attitude angles of the aircraft have been obtained to calculate the pointing angle in azimuth and elevation provided by using a double-antenna GPS/INS system. The size of the field of uncertainty (FOU) and the pointing accuracy are analyzed based on error theory, and it has been also measured using an observation camera installed next to the optical LOS. Our results show that the FOU of aircraft optical communications is 10 mrad without a filter, which is the foundation to acquisition strategy and scanning time.
KEYWORDS: Telecommunications, Laser communications, Signal detection, Laser systems engineering, Satellites, Signal processing, Optical communications, Process modeling, Visualization, Optical simulations
For an optical satellite link, the error sources that influence the pointing accuracy of the terminals include the attitude estimation error, ephemeris accuracy, and the boresight alignment error. It means an uncertainty cone (UC) exists for the spatial acquisition process. The acquisition process is a continuous adjustment for the visual axis of the two communication terminals, to enable them to detect the light signal from the other end, and finally realize the light closed loop. Beaconless acquisition algorithm and the corresponding acquisition process, modeling for spiral scan pattern and the simulation results of staring-scanning mode are presented. The UC scan range is 5 mrad, through the overlap with a spot divergence angle of 80 μrad, the total acquisition time is 98 s.
The fine tracking unit of composite axis of acquisition, pointing and tracking(APT) is a key component of space laser communication system. In order to prevent the principal axis in open-loop without proper input of control after started the tracking of auxiliary axis, which led to the target out of field. In a single detector composite shaft structure, we need to provide the accurate position of PZT volume feedback for the principle axis to control. This article has made an galvanometer position detective method of the single detector composite shaft structure. It provided the theory of circuit design and optimization plan. Researchers conducted a multiple sets of experiments. The experimental result shows that the galvanometer 1 "per deflection Angle, the detection circuit can retrieve 13 mV voltage change. At the same time, compared with the traditional camera calibration, we put forward a new calibration method which using optical autocollimator that the maximum error control within 1 ". Finally, the control formula is given and the error should be within 0.01mrad. So that the calibration precision of the detecting plate is improved.
KEYWORDS: Avalanche photodetectors, Receivers, Telecommunications, Avalanche photodiode receivers, Laser communications, Microcontrollers, Signal to noise ratio, Analog electronics, Control systems, Clocks
An avalanche photodiode (APD) receiver for intersatellite laser communication links is proposed and its performance is experimentally demonstrated. In the proposed system, a series of analog circuits are used not only to adjust the temperature and control the bias voltage but also to monitor the current and recover the clock from the communication data. In addition, the temperature compensation and multiplication gain control algorithm are embedded in the microcontroller to improve the performance of the receiver. As shown in the experiment, with the change of communication rate from 10 to 2000 Mbps, the detection sensitivity of the APD receiver varies from −47 to −34 dBm. Moreover, due to the existence of the multiplication gain control algorithm, the dynamic range of the APD receiver is effectively improved, while the dynamic range at 10, 100, and 1000 Mbps is 38.7, 37.7, and 32.8 dB, respectively. As a result, the experimental results agree well with the theoretical predictions, and the receiver will improve the flexibility of the intersatellite links without increasing the cost.
The intelligent control of simulation target with infrared imaging target in the indoor and outdoor
environment can effectively and quantitatively evaluated the parameters such as the minimum resolution
temperature difference(MRTD)and spatial resolution of airborne forward looking infrared, infrared detection
and tracking, infrared alarm, and etc.
This paper focused on introducing the working principles of the intelligent control simulation target of
Infrared imaging target, studying the thermal radiation characteristics of the infrared target surface material,
analyzing the influences of the infrared radiation energy distribution, and developing the intelligent control
simulation target with IR imaging target for hardware-in-the-loop simulation test. The intelligent control
simulation target which area was 5 ㎡ and concluded 44 infrared targets including two kinds of infrared
targets ,0.25m×0.25m, and 0.25m×0.5m, achieved 1℃~10℃ temperature simulation of target and the
background, and temperature control precision better than 0.5℃. Field test requirements were achieved by
actual test.
In order to provide a set of field test equipment for the infrared system of modern weapon equipments and other optics instruments, a set of large-scale resistance-type infrared target system was designed. First, the large-scale infrared target was designed in modular construction. It was decomposed into several independent and controllable units. Then the working principle of the system was introduced. Three modes of thermal exchange (conduction, convection and radiation) and the computing methods for each mode were given under thermal equilibrium conditions through modeling and simulating. Periphery electro-circuit and control software were carried out as well. Finally, the performance of the system was tested. Meanwhile novel ways of temperature compensation to improve the uniformity of the surface temperature of the target was introduced. The experimental results show that the infrared target could meet test requirements for infrared imaging weaponry which wavelengths from 8 μm to 14 μm. The temperature control precision can reach 0.5ms. In conclusion, the infrared target system can satisfy requirements of reliability, high precision, as well as strong anti-jamming and stabilization.
With the urgent need for the development of high data rate transmission of information and
high-resolution observation techniques, research on high-speed laser communications networking
technologies is imminent. This article analyzes the basic requirements of space laser communication
links and the technical difficulties and achieve in the network need to be solved. The optical principle
of the networking were proposed, studied technical solutions of a laser can be used for communication
between multiple targets simultaneously, designed with the rotating parabolic antenna to the base of the
optical multi-mirror stitching structure, as well as transmitting and receiving relay optical system with
APT system, a new technical approach was provided for the space laser communication link
Networking.
According to the parabolic features, for the incident light firing at the direction of focus, the reflected
light is parallel to the optical axis. But the energy efficiency is low for this type of surfaces, only small
portion of the energy can be received. So it is designed to form the multi-mirror mosaic structure with
parabolic base. The normal of each mirror is perpendicular to the tangent of the paraboloid. The size,
shape, number and the combination way of mirrors are designed and optimized according to the orbit
position and number. Each mirror is controlled to perform the movement in the horizontal and azimuth
directions, in this way the antenna has certain stability and light deflection. With this antenna,
communication can be realized for objects in different orientations at the same time for 360° in
horizontal direction and big field of view in azimuth direction.Finally, it prospected the application
foreground.
The blood vessels only in Human eye retinal can be observed directly. Many diseases that are not obvious in their early
symptom can be diagnosed through observing the changes of distal micro blood vessel. In order to obtain the high
resolution human retinal images,an adaptive optical system for correcting the aberration of the human eye was designed
by using the Shack-Hartmann wavefront sensor and the Liquid Crystal Spatial Light Modulator(LCLSM) .For a subject
eye with 8m-1 (8D)myopia, the wavefront error is reduced to 0.084 λ PV and 0.12 λRMS after adaptive optics(AO)
correction ,which has reached diffraction limit.The results show that the LCLSM based AO system has the ability of
correcting the aberration of the human eye efficiently,and making the blurred photoreceptor cell to clearly image on a
CCD camera.
KEYWORDS: Infrared radiation, Sensors, Black bodies, Measurement devices, Signal detection, Digital signal processing, Distance measurement, Transmittance, Combustion, Analog electronics
In order to realize the non-connect measurement on the power and character of jamming bomb, we carried out the
research on power measurement device of jamming bomb based on Infrared Radiation. First, the power and infrared radiant band of
the jamming bomb was summarized and refined. Then, ensuring the feature and power of jamming bomb was characterized by the
magnitude of Infrared Radiation. Afterwards, based on the theory of the above, a power measurement device of Infrared Radiation was simulated and developed. Including the selection of detector and the detector application design, analog signal processing and digital signal processing, using correlation measurement method to detect and calculate the power of device. Finally, the specific method and advantage of the device was introduced. The results of the experiment show that: the response time of the device is less than 3ms; the detection sensitivity is better than 3 x 108cm √HZ / W . The device successfully accomplished the accuracy measurement of Infrared Radiation between 1 to 20um wavelength with higher detection sensitivity and lower response time.
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