Intersatellite Laser Communication System Research Articles

Design and Simulation Analysis of Piezoelectric Ceramic Tube-Based Fiber Optic Nutator Applied to an Intersatellite Laser Communication System

The signal-receiving end of acquisition, pointing, and tracking (APT) systems applied to intersatellite laser communication terminals usually uses a fast-steering mirror (FSM) to control the fiber-coupling process, has a complex structural design, and induces large errors in the nonideal coaxial optical path. Herein, we propose a fiber-optic nutator using a piezoelectric ceramic tube (PCT) as the driving unit that allows scanning in the focal plane of the light signal to achieve active fiber coupling in the APT system. Specifically, this article describes the structural design principle of a PCT-based fiber optic nutator, establishes a simulation model of the mechanism, and proves the correctness of the simulation model by measuring the deflection angle of a PCT based on a parallel light collimator. The minimum accuracy of the designed nutator was 0.145 μm, the maximum nutation radius R was 20.09 μm, and the maximum nutation bandwidth was 20 kHz, as determined through simulation. Finally, the design parameters of the nutator were evaluated. The PCT-based fiber optic nutator, which met the design parameters, structurally replaced the fiber optic coupling component FSM and fine tracking camera in conventional APT systems successfully. Therefore, the PCT-based fiber optic nutator allows the active coupling control of signal light to a single-mode fiber (SMF) based on energy feedback on a theoretical basis and promotes the lightweight design of relay optical paths in APT systems. In addition, with future work in optimization of the nutation control algorithm, the scanning range and accuracy of the nutator can be improved.

Coarse-refined combined scanning method of beaconless inter-satellite laser communication system

Coarse-refined combined scanning method of beaconless inter-satellite laser communication system

Beacon correction method for inter-satellite laser communication

Positioning errors are caused by wavefront distortion owing to the thermal deformation of optical systems. To address this issue, we propose a restoration algorithm to correct for the beacon centroid, which is important for inter-satellite laser communication links. Based on the far-field distribution model of the distortion facula, the objective function is established to solve the wavefront distortion for reducing the pointing error of the optical communication system. The feasibility of this approach is verified by theoretical analysis and experimental verification, including in-orbit experimental verification. The proposed approach is likely to be useful for designing inter-satellite laser communication systems.

Received power attenuation due to the wave-front aberrations induced by the receiving optical antenna in an inter-satellite laser communication link

Due to the design defect, adjustment error, thermal deformation and gravity deformation in orbit, the bad optical antenna of the communication receiving terminal in an inter-satellite laser communication link will induce aberrations to the received wave-front. This will cause attenuation of the received power and deterioration of the bit error rate (BER) performance. The calculation model of the compensated and normalized received power is established when the received light spot is pointed at the center of the focal plane and the limited receiving radius is considered. The numerical results show that, for receivers with a single first-order Zernike mode wave-front aberration, the primary spherical aberration has the most influence on the received power attenuation, and for receivers with the same type aberrations, higher-order Zernike aberrations have more influence on that. The universality of the result for different antennas is verified by introducing a characteristic radius and a relative receiving radius. Some suggestions are proposed to lower the requirements of the wave aberrations control, thus reducing the difficulty of optical design, structural design, thermal design, assembly and adjustment. The outcome of this study would contribute to the design of the inter-satellite laser communication systems.

Point-ahead analysis and pre-pointing link stability study of intersatellite laser communication

The static bias error angle obviously affects pre-pointing links’ stability in the presence of vibration in intersatellite laser communication. The 2nd order point-ahead angle is a source of misalignment which was ignored in most solutions, and this is the concern of our paper. In this study, we present a further analytical investigation into the point-ahead angle in complex satellite maneuvering environment. Static bias error angle induced by the 2nd order point-ahead angle has been studied under different intersatellite links. The probability density function of the pre-pointing links’ outage has been derived in the presence of pointing jitter taking consideration of the static bias angle, and the link budget has also been analyzed. Simulation model of link stability has been established to verify the numerical results by the Monte Carlo method in Matlab-Simulink environment. The results have shown that the 2nd order point-ahead angle has a significant detrimental impact on link stability in long distance links. It is a neglectable factor. This work is dedicated to intersatellite laser communication system design.

Inter-satellite laser communication system based on double Risley prisms beam steering.

We designed an intensity modulation direct detection free-space laser communication terminal. In this system, the output power of the signal-modulated semiconductor laser amplified by two-stage fiber amplifier is 2W, and the modulation contrast is 15dB. Tracking of the incident beam and demodulation of the communication signal are realized by using a quadrant avalanche photodiode (APD). By means of rotating double Risley prisms, the ranges of the pitching angle and azimuth angle are ±35 and ±180 deg, respectively. The focal length of the transceiver lens is 125mm, and the final communication field of view is 4mrad. Without error correction coding, the sensitivity of -44.5 dBm was achieved, while the bit-error rate was below 10-3 at 70Mbps. We also established a laser communication experiment at the laboratory; the platform jitter below 5Hz can be effectively suppressed. The laser communication system has a compact structure, low power consumption, and effective suppression of low-frequency and high-amplitude angle jitter of the platform. The experiments demonstrate that the laser communication terminal can be used in an inter-satellite laser communication with a distance of thousands of kilometers. The theoretical analysis and experimental results are presented in the paper.

The Optimization Design of Sub-Regions Scanning and Vibration Analysis for Beaconless Spatial Acquisition in the Inter-Satellite Laser Communication System

We mainly report an efficient approach to optimize the design of beaconless spatial laser acquisition. In order to analyze the influence of vibration environment on the beaconless spatial acquisition, a demonstration of an efficient method will be presented to simulate the level of satellite platform vibration. An important power spectral density (PSD) model of satellite platform vibration used by the European Space Agency is introduced. Then through LABVIEW, a simulated vibration waveform is generated, and the simulated PSD has a basic consistency with the in-orbit measurement spectral line, referring to the design of the filter, generating the Gaussian white noise sequence, filtering the pseudorandom signal and the whole processing procedure of parameter matching. The variation interval of the vibration amplitude is from −100 to 40 μrad. Then, the model of beaconless acquisition is proposed, which uses the spiral scan pattern, laser with a divergence angle of 80 μrad scan in an uncertainty cone (UC), and also the scan coupled with the simulated vibration is given. Through the beaconless acquisition program, the vibration is suppressed between −10.7 and 5.9 μrad; when the overlap factor is selected as 10%, it does not produce any leakage scanning area. It can be used for a wide variety of platforms. This new method will be good for analysis and test of beaconless spatial acquisition algorithm. Finally, the description of acquisition duration, which mainly includes the fast steering mirror spiral scan and the mechanical rotary table step scan, is introduced. And the corresponding optimal selection method of sub-region is proposed; the design of 1.6-mrad scanning pattern with 7 × 7 sub-regions in the 8-mrad acquisition UC is given. Through the actual measurement, the acquisition time is 18.21 s, the tracking error is better than 0.4 μrad.

Pointing and tracking errors due to low-frequency deformation in inter-satellite laser communication

ABSTRACTA Gaussian random-phase screen (GRPS) model is proposed to represent the low-frequency wave-front deformation in inter-satellite laser-communication links. The model is used to investigate mutual-alignment errors comprising pointing and tracking errors caused by the low-frequency deformation. Theoretical analysis and numerical simulation show that the GRPS root-mean-square (RMS) value, pointing error, and tracking error increase with the amplitude factor and the scale length in the model. The expectation of RMS increases in the form of a linear function with and increases in the form of a cubic function with . The expectations of the pointing and tracking errors increase with increases in the expected values for and . For a specific pointing error or tracking error, the 99.5% confidence interval of the RMS of the low-frequency wave-front deformation is provided. From this confidence interval, the lower limit of the processing precision of optical antennas corresponding to certain mutual-alignment errors can be predicted. These conclusions are expected to be instrumental in designing inter-satellite laser-communication systems.

Radiation-induced mismatch effect on performances of space chaos laser communication systems.

Chaotic modulation serves as an excellent scheme to enhance the confidentiality of space laser communication systems. Considering radiation and intensity scintillation, we establish bit error rate (BER) computation models for both an inter-satellite chaos laser communication system and a satellite-to-ground chaos laser communication system. Based on such models, numerical simulations are conducted to investigate the mismatch effect on BER performance of these two typical systems. For an inter-satellite system, radiation can induce great parameter mismatches. For a satellite-to-ground system, the BER only slightly rises due to intensity scintillation being a more dominant deterioration effect than radiation. Our work has good reference value for the practical design of space chaos laser communication systems.

Approach for recognizing and tracking beacon in inter-satellite optical communication based on optical flow method.

In inter-satellite laser communication systems, accurate positioning of the beacon is essential for establishing a steady laser communication link. For inter-satellite optical communication, the main factor affecting the acquisition and tracking of the beacon is the background noise, such as stellar background light. In this study, we considered the effect of the background noise on a beacon in inter-satellite optical communication and proposed a new recognition algorithm for the beacon, which uses the optical flow vector obtained from the image data. We verified the feasibility of this method by performing simulation analysis and experiments. Both simulation and experiments showed that the new algorithm could accurately obtain the position of the centroid of the beacon under the effect of the background light. Furthermore, considering the identification probability of a light spot through the background light, the locating accuracy of the new algorithm was higher than that of the conventional gray centroid algorithm. Therefore, this new approach would be beneficial for the design of satellite-to-ground optical communication systems.

Modeling and reality analysis of beaconless spatial acquisition for intersatellite laser communication system

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.

Using top-hat beam to improve the performance of the inter-satellite laser communication

The profile of transmitting beams in inter-satellite optical links significantly impacts communication performance, shaping the general Gaussian transmitting beam into a far field top-hat profile may improve the performance of the inter-satellite laser communication system. The calculations show that this scheme would at least reduce beaconless acquisition time by nearly 63%, and may reduce the outage probability of communication link several orders of magnitude. In addition, the tracking error allowance of communication terminals would at least increase to 1.65 times while keep communication link stable. Use of top-hat beam is quite helpful to build and operate robust inter-satellite optical communication terminals at lower technical risks and cost.

Strehl ratio versus localized distortion in reflectors in lasercom

In intersatellite laser communication (lasercom), the Strehl ratio (SR) is usually used to characterize the transmitter-beam quality. We study its dependence on localized distortion in reflectors based on the Gaussian model. We show that the transmitter-beam quality depends on three parameters of localized distortion and changes regularly with their increase. Localized distortion in reflectors influences the beam quality near the depth of 0.4 λ, which does not depend on other distortion parameters. To reduce the impact of localized deformation on the beam quality, we use the peak-to-valley (PV) value to evaluate the machining precision of mirrors and show that it should be much better than 0.8 λ. The results obtained can be used in designing intersatellite laser-communication systems.

Influence of reflector temperature gradients on bit-error rate in periscope laser communication systems in the presence of detector noise and platform vibrations

We consider the influence of thermal deformations of elliptic reflectors in periscope laser communication terminals on the bit-error rate (BER) taking into account the satellite-platform vibrations and the detector noise. We study the relationship between the average BER and temperature gradients of elliptic reflectors in inter-satellite laser communication systems at different values of the light beam wavelength and truncation rate, and different vibration amplitudes. The average BER increases with increase in the vibration amplitude, and it is noteworthy that the average BER increases with increase in the beam truncation rate, which contradicts the result obtained in [1] without taking noise into account. We find that for some temperature gradients there is an optimum communication wavelength that provides the minimum average BER. We use the back-fixing method for fixing the elliptic reflectors, which has proved to be much less sensitive to temperature gradients compared to the traditional around-fixing method by a press board.

Received Signal Strength Reduction Analysis Based on the Wavelet Model in Intersatellite Laser Communications

The performance of intersatellite laser communication system can be affected by optical antenna deformations. A deformation model is established based on wavelet analysis for diversified deformations caused by processing technique and complex environment of the outer space. Numerical analyses show that the reconstruction error of a localized irregular deformation by wavelet could achieve 10-12 level, which is far better than Zernike polynomials to some extend. Relationships between diversified antenna deformations and the effect on received signal strength are derived based on the model. According to simulation results, the effect of deformation on received signal strength increases with the dilation factor of the model, decreases with the shift factor of the model, and tends to increase with irregular fluctuations with the linear increase of wavelet coefficient of the model. This study may be of some help in the design of intersatellite laser communication systems.

Mutual alignment errors analysis based on wavelet due to antenna deformations in inter-satellite laser communications

Wavelet analysis is employed in the paper to model diversified optical antenna deformations in inter-satellite laser communications. Mutual alignment errors, which comprise pointing and tracking errors, caused by the deformations are investigated with the model. Theoretical and numerical analysis show that both errors increase with the dilation factor of the model. Tracking error increases monotonously with the shift factor of the model, while pointing error increases first, and then decreases. When the deformation can be well approximated to a constant, both errors fluctuate periodically with the coefficient of the model. Otherwise, there is no obvious regularity for both errors with the increase of the coefficient. A reference for the machining precision of optical antennas is presented, and a method to reduce the effect of deformations is recommended. It is hoped that the study can contribute to improve the performance of inter-satellite laser communication systems.

非高斯畸变对星间光通信瞄准偏差的影响

非高斯畸变对星间光通信瞄准偏差的影响

Securing Funds for Research or Product Development

Doppler shift due to relative movement between satellites must be taken into consideration in intersatellite laser links. The degradation of differential phase-shift keying (DPSK) receiver performance caused by Doppler shift is assessed. In order to simplify the complexity of the receiver, we discuss conditions that will bring the new design concept for a robust laser communication system in space, which does not require precise active control. When the precise active control has to be used, the impact of frequency drifts relative to optical filter's center frequency becomes evident. Optimum bandwidths of optical filters yielding optimum performance over the entire range of frequency shifts are determined to further improve the receiver performance. The results obtained here will be helpful in the design of DPSK/self-homodying intersatellite laser communication systems. C 2010 Society of Photo-Optical Instrumentation Engineers.

Pointing error due to temperature distribution of SiC reflectors in intersatellite laser communications

Wave-front aberrations due to thermal deformation of elliptical reflectors in periscopic laser communication terminals are studied, and are fitted by Zernike elliptical polynomials. The relationship between pointing error and temperature distribution of elliptical reflectors in intersatellite laser communication systems is researched. The back-fixing method is introduced for fixing the elliptical reflectors, and is proven to reduce pointing error compared to the traditional around-fixing method using a press board. It is shown that the difference between uniform temperature and reference temperature has a much stronger influence than the temperature gradient. For the back-fixing method, the pointing error changes periodically as the uniform temperature changes with a period value of 1.6 degrees C, and the maximum pointing error value is 16.7murad. The result also tells us that, if the difference between uniform temperature and reference temperature is within 1.0 degrees C, there is no pointing error caused by back-fixed reflectors. We hope this work can contribute to the thermal control of elliptical reflectors in intersatellite laser communication terminals.

Receiver power penalty due to localized distortion induced by transmission-type optical antenna in inter-satellite laser communications

Based on a truncated ellipse Gaussian model for localized distortion in transmission-type optical antenna, the receiver power penalty due to localized wavefront deformation is researched. It is shown that the receiver power depends on distortion deepness h, radii a and b, and position d, and changes regularly with them. Localized distortion has the greatest influence on receiver power at a depth of h ≈ 1.45λ, which does not depend on other deformation parameters. The maxima of the receiver power penalty for different distortion radii are given. To reduce the impact of localized distortion on the receiver power, the machining precision of lenses should be better than 1.45λ. We hope the results can be used in the design of intersatellite laser communication systems.