A satellite dedicated for quantum science experiments, has been developed and successfully launched from Jiuquan, China, on August 16, 2016. Two new optical ground stations (OGSs) were built to cooperate with the satellite to complete satellite-ground quantum experiments. OGS corrected its pointing direction by satellite trajectory error to coarse tracking system and uplink beacon sight, therefore fine tracking CCD and uplink beacon optical axis alignment accuracy was to ensure that beacon could cover the quantum satellite in all time when it passed the OGSs. Unfortunately, when we tested specifications of the OGSs, due to the coarse tracking optical system was commercial telescopes, the change of position of the target in the coarse CCD was up to 600μrad along with the change of elevation angle. In this paper, a method of reduce alignment error between beacon beam and fine tracking CCD is proposed. Firstly, OGS fitted the curve of target positions in coarse CCD along with the change of elevation angle. Secondly, OGS fitted the curve of hexapod secondary mirror positions along with the change of elevation angle. Thirdly, when tracking satellite, the fine tracking error unloaded on the real-time zero point position of coarse CCD which computed by the firstly calibration data. Simultaneously the positions of the hexapod secondary mirror were adjusted by the secondly calibration data. Finally the experiment result is proposed. Results show that the alignment error is less than 50μrad.
Infrared small target is easy submerged in the complex background, to improve the ability of detecting target, which by inhibiting the background to enhance the target signal. Focusing on the shortcomings of the isotropic background prediction method, a kind of improved anisotropic infrared background prediction method (IABP) is proposed. According to differences of local gradient character among target region, smooth background region and undulate background region, the edge stopping function of anisotropic partial differential equation is improved. Then the mean of the two least values of the edge as the prediction value of the background. Finally in order to extract the candidate target and reduce the false alarm rate of the real target, which the difference between the background image and the original image is processed. Experimental results show that: 1) improved anisotropy of background prediction for different scenes can obtain good background prediction effect; 2) improved anisotropic background predication for the signal-noise ratio (SNR) was lower than 2.3db could be loyal to the true background of the original image to the maximum extent, presenting a superior overall performance to other background prediction methods.
In this paper, a telescope control method to reject ground-based disturb is proposed to enhance the tracking precision of telescope systems. Telescope systems usually suffer some uncertainouter disturbances, some disturbance come from the torque disturb such as friction orwind loads, some of the others may come from the platform. For astronomical telescope, especially relative large volume telescope, disturb from ground istransferred to the telescope via the pier foundation. And the main mount of disturb is the resonance frequency of pier foundation. The frequency is about 10Hz.A complete vibration test was carried out on a quantum satellite-ground communicationground telescope. Some conclusion is achieved. And a control method based on data fusion to rejecting ground-based disturbance is proposed. The test showed that the method could reduce the track error from 1.5 angular second to 0.28 angular second.
In this paper, a method of acquisition between optical ground station and quantum communication satellite named Micius for establish optical links is proposed. The acquisition technological specification of the optical ground station system is analyzed. The acquisition strategy of optical ground station is designed. In order to point accurately to quantum satellite for optical ground station, system error modifying method is designed, using the telescope mount model to improve the absolute pointing precision. Finally the experiment result is proposed. Results show that the correction accuracy is better than 5μrad. The acquisition time is less than 5 seconds.
In this paper, a friction compensating method based on data fusion in telescope controller is proposed to enhance the tracking precision of telescope systems. Telescope systems usually suffer some uncertain disturbances, such as friction, wind loads and other unknown disturbances. Especially, when telescope change speed direction, the friction is the dominate track error. Thereby, to ensure the tracking precision, the friction compensating method which can attenuate the influence of friction is introduced. Besides, to improve the friction identify accuracy, a data fusion method which fuse accelerometer and encoder is adopted. Finally, a few comparative experimental results show that the proposed control method has excellent performance for reducing the tracking error of telescope system.
The free space optical (FSO) communication system has attracted many researchers from different countries, owning to its advantages such as high security, high speed and anti-interference. Among all kinds of the channels of the FSO communication system, the atmosphere channel is very difficult to deal with for two typical disadvantages at least. The one is the scintillation of the optical carrier intensity caused by the atmosphere turbulence and the other is the multipath effect by the optical scattering. A lot of studies have shown that the MIMO (Multiple Input Multiple Output) technology can overcome the scintillation of the optical carrier through the atmosphere effectively. So the background of this paper is a MIMO system which includes multiple optical transmitting antennas and multiple optical receiving antennas. A number of particles such as hazes, water droplets and aerosols exit in the atmosphere widely. When optical carrier meets these particles, the scattering phenomenon is inevitable, which leads to the multipath effect. As a result, a optical pulse transmitted by the optical transmitter becomes wider, to some extent, when it gets to the optical receiver due to the multipath effect. If the information transmission rate is quite low, there is less relationship between the multipath effect and the bit error rate (BER) of the communication system. Once the information transmission rate increases to a high level, the multipath effect will produce the problem called inter symbol inference (ISI) seriously and the bit error rate will increase severely. In order to take the advantage of the FSO communication system, the inter symbol inference problem must be solved. So it is necessary to use the channel equalization technology. This paper aims at deciding a equalizer and designing suitable equalization algorithm for a MIMO free space optical communication system to overcome the serious problem of bit error rate. The reliability and the efficiency of communication are two important indexes. For a MIMO communication system, there are two typical equalization methods. The first method, every receiving antenna has an independent equalizer without the information derived from the other receiving antennas. The second, the information derived from all of the receiving antennas mixes with each other, according to some definite rules, which is called space-time equalization. The former is discussed in this paper. The equalization algorithm concludes training mode and non training mode. The training mode needs training codes transmitted by the transmitter during the whole communication process and this mode reduces the communication efficiency more or less. In order to improve the communication efficiency, the blind equalization algorithm, a non training mode, is used to solve the parameter of the equalizer. In this paper, firstly, the atmosphere channel is described focusing on the scintillation and multipath effect of the optical carrier. Then, the structure of a equalizer of MIMO free space optical communication system is introduced. In the next part of this paper, the principle of the blind equalization algorithm is introduced. In addition, the simulation results are showed. In the end of this paper, the conclusions and the future work are discussed.
For large-aperture optical telescope, compared with the performance of azimuth in the control system, arc second-level
jitters exist in elevation under different speeds' working mode, especially low-speed working mode in the process of its
acquisition, tracking and pointing. The jitters are closely related to the working speed of the elevation, resulting in the
reduction of accuracy and low-speed stability of the telescope. By collecting a large number of measured data to the
elevation, we do analysis on jitters in the time domain, frequency domain and space domain respectively. And the
relation between jitter points and the leading speed of elevation and the corresponding space angle is concluded that the
jitters perform as periodic disturbance in space domain and the period of the corresponding space angle of the jitter
points is 79.1″ approximately. Then we did simulation, analysis and comparison to the influence of the
disturbance sources, like PWM power level output disturbance, torque (acceleration) disturbance, speed feedback
disturbance and position feedback disturbance on the elevation to find that the space periodic disturbance still exist in the
elevation performance. It leads us to infer that the problems maybe exist in angle measurement unit. The telescope
employs a 24-bit photoelectric encoder and we can calculate the encoder grating angular resolution as 79.1016'', which is
as the corresponding angle value in the whole encoder system of one period of the subdivision signal. The value is
approximately equal to the space frequency of the jitters. Therefore, the working elevation of the telescope is affected by
subdivision errors and the period of the subdivision error is identical to the period of encoder grating angular. Through
comprehensive consideration and mathematical analysis, that DC subdivision error of subdivision error sources causes
the jitters is determined, which is verified in the practical engineering. The method that analyze error sources from time
domain, frequency domain and space domain respectively has a very good role in guiding to find disturbance sources for
large-aperture optical telescope.
The principles of coherent detection and balanced detectors are analyzed respectively in this article. It mainly talked about the balance detector applications in coherent detection. Obtained by the theoretical analysis that we can not only make full use of the local oscillator optical power but also eliminate the noise of the LO light more effectively by using the balanced detector. The most important is that it can improve the SNR of the system. This paper also makes a research on the factors that affect the performance of the balanced detector. The simulation results show that the response of the photo-diode consistency should be gain at least 90% in order to improve the SNR effectively. It further validates that the laser intensity noise indeed declined by using the balanced detector.
A feedforward control based on data fusion is proposed to enhance closed-loop performance. The target trajectory as the observed value of a Kalman filter is recovered by synthesizing line-of-sight error and angular position from the encoder. A Kalman filter based on a Singer acceleration model is employed to estimate the target velocity. In this control scheme, the control stability is influenced by the bandwidth of the Kalman filter and time misalignment. The transfer function of the Kalman filter in the frequency domain is built for analyzing the closed loop stability, which shows that the Kalman filter is the major factor that affects the control stability. The feedforward control proposed here is verified through simulations and experiments.
Proc. SPIE. 9677, AOPC 2015: Optical Test, Measurement, and Equipment
KEYWORDS: Detection and tracking algorithms, Error analysis, Control systems, Computer programming, Optical testing, Signal processing, Servomechanisms, Control systems design, Performance modeling, Systems modeling
According to the larger error when reversing in photoelectric tracking control system, the improved cascade Active Disturbance Rejection Controller (ADRC) is put forward to improve the system position tracking performance and tracking precision. First of all, this essay analyses the controlled object model and system control strategy; Then, it gives design method of the improved cascade ADRC; Finally, in order to analyses the improved cascade’s better control performance, in the condition of the same input signal ,the improved cascade ADRC, conventional ADRC-ADRC and traditional PI-PI controller are used in photoelectric tracking control system to do comparative experiment. The experiment results show that the improved cascade ADRC's performance is better than other two algorithms, the tracking error and the steady state mean square error are significantly reduced, tracking accuracy is significantly improved. The improved cascade ADRC is an appealing solution in dealing with industrial control system problems where uncertainties and interference abound.
In this paper, an improved Active Disturbance Rejection control (ADRC) method is proposed to enhance the tracking precision of telescope if the telescope runs in a low velocity. Low velocity telescope system usually suffers some obvious nonlinear disturbances, such as nonlinear friction and unknown external disturbance. Thereby, to ensure the tracking precision, multiple loops control structure is a common control method in telescope system, which includes current loop, velocity loop and position loop. The proposed control method is used in the velocity loop which consists of a PD controller and an Extend State Observer (ESO). The ESO is designed to estimate the disturbance involved in the telescope system. Besides, the PD controller is designed to stabilize the closed-loop system. Furthermore, this control method theoretically guarantees a prescribed tracking performance and final tracking accuracy. Finally, the experiment results show that the proposed control method has excellent performance for reducing the tracking error of low velocity.
There are several advantages offered by free space optic systems compared with conventional radio frequency systems. As a consequence of shorter wavelengths, the high directivity of the transmitted beam makes acquisition and pointing difficult, thus an imaging system is set up for acquisition and pointing. Optical wave front distortions induced by atmospheric turbulence result in a spreading of the beam leads to image jitter take place in the focal plane, where the image sensor is. The behavior of the image jitter can be described in a statistical manner. Consequently, the size, which is a very important parameter to an image sensor, can be determined by the statistical quantity of image jitter, which customarily is the root mean square (RMS) image displacement. The quantity of the RMS image displacement is as a function of several measurable parameters. In this paper, variations of the estimated RMS image displacement were calculate and discussed in detail. The calculation showed good agreement with the experimental results conducted with a propagation path length of 96 km. The optimal sizes of image sensors that are used for some specific circumstances were analyzed and proposed based on the RMS image displacement.
Free-Space Quantum Communication(FSQC) based on the BB84(Bennett-Brassard 1984) protocol makes use of two groups of conjugate basis polarized photon as the carriers of information to realize the communication between a satelits and a group station. Polarization would show some problems like the contrast of polarization to be worser and the polarization-basis unmatched when transfering. In order to achieve the BB84 protocol, ground station needed to track and calibrate for the polarization zero direction of the satellite equipments. So the polarization maintaining and polarization-basis calibrating is one of the key technologies of the FSQC system. Firstly, this paper established the mathematical model of polarization in the FSQC system, and then derived the mathematical relation between the contrast of polarization and the phase delay in theory. Some proposals of Optical System designs have been suggested in the paper. Finally the problem of dynamic polarization-basis in the satellite-ground link had been analysed and the dynamic characteristic of the deviation angle of polarization-basis in this paper.
The liquid crystal beam steering technology with low driving voltage, high diffraction efficiency and without the
effect of mechanical inertia，is regard as a potential technology in the field of non-mechanical beam steering. Liquid
crystal spatial light modulator (LCSLM) can be applied as a beam steering control device in laser communication, and it
can realize the programmable control in real time. And compared with fast steering mirror (FSM), which is widely used
at present, LCSLM is smaller, lighter and lower power consumptive in a non-mechanical way, so it’s convenient to
control. But the system bandwidth is a restricted problem in the research. In this article, the principle of beam steering
with LCSLM is introduced firstly. A beam steering bench is set up using reflective pure-phase LCSLM from BNS. The
offset of beam spot is detected by the CCD and a classic PI close-loop control experiment is designed to test the system
bandwidth. And then the factors which restricted the control bandwidth are analyzed. Considering the effect of the CCD’
frame rate, the PSD with higher frame rate is used in the control system and the data model of the liquid crystal is tested.
A controller is designed based on the data model and the bandwidth is improved observably.
Quantum entanglement is the main resource to endow the field of quantum information processing with
powers that exceed those of classical communication and computation. Due to low absorption and
negligible nonbirefringent character in atmosphere, optical free space therefore serves as the most
promising channel for large-scale quantum communication by use of satellites and ground stations. The
acquisition, tracking and pointing (ATP) system is one of the most important parts of quantum
experiment system, and it controls a transmitting and receiving laser beam within a few micro radians
jitter because of using an extremely narrow beam divergence of several micro radians. This paper
introduces the cascade ATP systems for 100km quantum entanglement distribution experiment among
Charlie, Bob and Alice station. The specification and optical diagram of each ATP system are presented.
The ATP system of Alice station is described in detail，it has coarse, fine and ultra-fine loop. In the
100km quantum entanglement distribution experiment, a tracking error of 4μrad is achieved for 70Hz
bandwidth. The ATP strategy in this experiment can be used in the prospective satellite-to-ground
In the control system of a CCD-based tracking loop for a fast steering mirror (FSM), the most effective method often employed to improve pointing performance is to increase high gain of the control system for a high bandwidth, which, however, usually suffers a great deal from a low CCD sampling rate and the mechanics of the FSM. Moreover, the amount of time delay engendered by sampling and data processing can significantly reduce the performance of a closed-loop system. Therefore, a tentative approach to the implementation of a CCD-based tracking control system with acceleration feedback is proposed. In theory, the position open loop is made of double integrators with a high bandwidth of the acceleration feedback loop; in fact, however, the acceleration open loop of the FSM response includes a quadratic differential, and it is very difficult to compensate a quadratic differential with an integral algorithm. To solve this problem, a novel acceleration closed system such as a bandpass filter is proposed. The position is reconstructed into a simple first-order filter instead of a third-order control system. In addition experimental results show that the acceleration feedback proposed here can effectively enhance the bandwidth of the closed-loop system and its trajectory tracking and pointing performance.