Laser Communication System Research Articles

Free-space laser communication system with rapid acquisition based on astronomical telescopes

The general structure of a free-space optical (FSO) communication system based on astronomical telescopes is proposed. The light path for astronomical observation and for communication can be easily switched. A separate camera is used as a star sensor to determine the pointing direction of the optical terminal's antenna. The new system exhibits rapid acquisition and is widely applicable in various astronomical telescope systems and wavelengths. We present a detailed analysis of the acquisition time, which can be decreased by one order of magnitude compared with traditional optical communication systems. Furthermore, we verify software algorithms and tracking accuracy.

Performance analysis of a free-space laser communication system with a Gaussian Schell model

In practice, due to reasons related to the characteristics of the laser device and the inevitable error of the processing technique, a laser beam emitted from a communication terminal is represented by the Gaussian–Schell model. The incident optical intensity at the receiver aperture is affected by the source coherence parameter through atmospheric turbulence. With full consideration of both the average optical intensity and the scintillation, the statistical distribution of the optical intensity and the average bit error rate (BER) of an on-off keying (OOK) receiver is obtained. The results indicate that the effect on the degradation of the average optical intensity is reduced with a smaller beamwidth. The performance of the OOK receiver degrades drastically with the increasing source coherence parameter. Moreover, when the beamwidth becomes larger, the BER0 with a consistent source coherence parameter shifts to the side of lower BER. The goal of this work is to improve the redundancy design of the laser communication receiver system.

Far-field correlation of bidirectional tracking beams due to wave-front deformation in inter-satellites optical communication links.

In some applications of optical communication systems, such as inter-satellites optical communication, the correlation of the bidirectional tracking beams changes in far-field as a result of wave-front deformation. Far-field correlation model with wave-front deformation on tracking stability is established. Far-field correlation function and factor have been obtained. Combining with parameters of typical laser communication systems, the model is corrected. It shows that deformation pointing-tracking errors θ(A) and θ(B), far-field correlation factor δ depend on RMS of deformation error rms, which decline with a increasing rms including Tilt and Coma. The principle of adjusting far-field correlation factor with wave-front deformation to compensate deformation pointing-tracking errors has been given, through which the deformation pointing-tracking error is reduced to 18.12″ (Azimuth) and 17.65″ (Elevation). Work above possesses significant reference value on optimization design in inter-satellites optical communication.

通用自适应光学波前实时处理机的设计

In order to satisfy the requirement of high speed and real-time processing for 1000-unit class adaptive optics(AO) system in telescope and free space laser communication system, a generic high speed and real-time processing platform on one board is proposed. Multi-core center processing unit(CPU) is arranged for wave-front real-time computing, combined with high speed frame-grabber, to achieve the purpose of high frame-frequency.Xenomai real-time operation system combined with Linux operation system is used to satisfy the requirement of low latency. A compact real-time controller is assembled in one computer. Computing power of 51 giga floatingpoint operations per second(GFLOPS) and communication band-width of 102 GB/s are achieved in a computer with 6-core, via vector instruction optimization and processing in parallel with multi-core CPU. The emulation result shows that processing frequency can be up to 2000 Hz for 1145-unit AO system with 949 sub-apertures, and the delay is below 240 ms. This processor is introduced to AO system for laser communication via adjusting the parameters, and Strehl ratio of 0.61 is achieved after correction. This indicates the scheme can satisfy the requirement of high speed and low latency for AO system with actuators below 1145 unit, with the merit of general purpose.

Design and Implementation of MOEMS Based Ground to Satellite Free Space Optical Link Under Turbulence Condition

Non-mechanical beam steering techniques are commonly used in free space laser communication systems to avoid the use of massive opto-mechanical components. In this paper, we demonstrate an array-of-arrays of micro-opto-electro-mechanical system (MOEMS) based mirrors as a replacement for a large aperture reflective single-element mirror for ground to satellite optical links along with its associated electronic drive circuitry and FPGA based interface. The performance of the free space optical (FSO) communication link in terms of beam variance under atmospheric turbulence conditions is discussed.

自由空间激光通信系统中多通道滤光膜的研制

自由空间激光通信系统中多通道滤光膜的研制

一点对多点同时空间激光通信光学跟瞄技术研究

一点对多点同时空间激光通信光学跟瞄技术研究

Research on tunable local laser used in ground-to-satellite coherent laser communication

In order to realize homodyne reception and Doppler frequency shift tracking in ground-to-satellite coherent laser communication, a local laser is experimentally demonstrated in this Letter. It is realized based on modulation-sideband injection locking, and has a 10 GHz tuning range, a 1 THz/s tuning rate, a 5 kHz linewidth, and 16 mW of output power. When applied to a Costas loop in a coherent laser communication system, the local laser can achieve ±5 GHz Doppler frequency shift tracking with a 20 MHz/s frequency shift rate, which is sufficient for the ground-to-satellite coherent laser communication.

The influence of space irradiated PIN photodetector on BER in satellite laser communication system

By analyzing the radiation dose on PIN photodetectors in space radiation environment, the variation of photocurrent and dark current after radiation is obtained. On the basis, the bit error rate of satellite laser communication based on space radiation dose of PIN photodetectors is established. According to simulation, when radiation dose is about 1.6×103Gy and 7×104Gy, bit error rate reaches 10−6 induced by 50MeV and 10MeV protons separately; and when radiation dose is within the range of 5×10Gy–6×105Gy, electrons and gamma-ray irradiation also cause increase in bit error rate to 10−6. The principle of damage dose on bit error rate is investigated, and the influence of decision threshold on bit error rate is further discussed. The result shows that when radiation dose is 1MGy, if decision threshold is increased from 4.3×10−7A to 5.5×10−7A, bit error rate will decrease about 4 orders of magnitude. Hence, a proper decision threshold can improve system bit error rate efficiently.

Wander of a Gaussian-Beam Wave Propagated Through a Non-Kolmogorov Turbulent Atmosphere

Both increasing experimental evidence and some results of theoretical investigation have shown that there exist two kinds of turbulence in the aerosphere, Kolmogorov and non-Kolmogorov turbulence. Thus, it is necessary to improve the theory of optical wave propagation through atmospheric turbulence, namely, study the laser-beam propagation in non-Kolmogorov turbulence, before analyzing the joint influence of the Kolmogorov turbulence and non-Kolmogorov one on satellite laser communication. The beam wander will lead to the performance degradation of satellite laser communication systems and exert an influence on the achievement and stability of its links. In this paper, we consider a theoretical power spectrum of refractive-index fluctuations with a generalized power law in order to derive the variance of Gaussian-beam wave wander in weak turbulence for a horizonal path and analyze the influence of spectral power-law variations on the beam wander. We show that the expression for the beam-wander variance is of concise closed form and independent of the optical wavelength.

Performance evaluation of adaptive optics for atmospheric coherent laser communications

With extremely high sensitivity, the coherent laser communications has a large potential to be used in the long-range and high data-rate free space communication links. However, for the atmospheric turbulent links, the most significant factor that limits the performance of the coherent laser communications is the effect of atmospheric turbulence. In this paper, we try to integrate the adaptive optics (AO) to the coherent laser communications and analyze the performances. It is shown that, when the atmospheric turbulence condition D/r0 is not larger than 1, can the coherent laser communication system works well without the correction of an AO system. When it is in the gentle turbulent condition (around D/r0 = 2), only the tip and tilt correction can improve the mixing efficiency and the bit-error rate (BER) significantly. In the moderate (around D/r0 = 10) or relatively strong (around D/r0 = 17) turbulent condition, the AO system has to correct about 9 or 35 turbulent modes or more respectively to achieve a favorable performance. In conclusion, we have demonstrated that the AO technique has great potential to improve the performances of the atmospheric coherent laser communications.

Transmission characteristics of a Raman-amplified atomic optical filter in rubidium at 780 nm

The transmission characteristics of a Raman-amplified atomic filter that can be used to detect fairly weak signals in free-space quantum-key distribution or laser communications are analyzed and discussed in the coherent and incoherent pump fields respectively. The theoretical model for the calculation of the transmission characteristics of a ground-state Raman-amplified Faraday dispersion atomic optical filter based on Raman gain and Faraday rotation is presented. The results show that the filter in a coherent pump field can achieve higher transmission and larger tunability than that in an incoherent pump field due to elimination of pumping detuning. In addition, the filter has a large scale tunability over 3.5 GHz via the Faraday transmission peak adjusted while its bandwidth is only 66 MHz, which is useful for free-space laser communication and lidar systems.

Design of data communication and management system for ground test and verification devices of space laser communication

Verification of a space laser communication system's parts or of component-level, terminal-level, and system-level performance using ground test and verification devices on the ground before launch is vital. In this paper, a data communication and management system is proposed, which is an important part of the ground test and verification devices system and manages the test process and impacts on the measurement results directly. We improved the existing hardware buses to make up the hardware part, and also designed the software part. Several typical tests were performed, and the results show that the maximum time delay is less than 50ms. The developed data communication and management system is demonstrated to be a high-performance system which can meet the requirements in our project.

湍流大气中激光通信系统接收光功率的优化研究

湍流大气中激光通信系统接收光功率的优化研究

用于空间激光通信系统的近红外分色片设计与研制

用于空间激光通信系统的近红外分色片设计与研制

Capacity-Achieving Distributions for the Discrete-Time Poisson Channel—Part II: Binary Inputs

Discrete-time Poisson (DTP) channels exist in many scenarios including space laser communication systems which operate over long distances and which can be corrupted by reflected and scattered light. Through simulation, binary-input distributions have been observed to be optimal in many cases, however, little analytical work exists on conditions for optimality or the form of optimal signalling. In this second part, the general properties of Part I are extended to the case of DTP channels where binary-inputs are optimal. Necessary and sufficient conditions on the optimality of binary (i.e. two mass point) distributions are presented by leveraging the general properties of DTP capacity-achieving distributions. Closed-form expressions of the capacity-achieving distributions are derived in several important special cases including zero dark current and for high dark current. Numerical results are presented to elucidate the developed analytical work.

FPGA Implementation for CCD Driving and Laser Spot Position Detection

CCD sensor can be used as the imaging device in the initial aiming processing for the beacon laser, and can also be used as the detecting device for the communication lasers optical axis alignment error of the targeting captured trace (APT) unit in space laser communication system. In this paper, based on a double-FPGA structure, we proposed technical solutions to realize the imaging CCD sensor driving and the laser spot position detection algorithm for the CX285AL image sensor by using the overall design of the system block diagram. The spot position detection wave door track centroid algorithm for CCD sensor is also studied by using the analysis of laser transmission characteristics of the atmospheric turbulence. The simulation analysis and field tests have been verified the feasibility of this approach.

Performance analysis of OOK, BPSK, QPSK modulation schemes in uplink of ground-to-satellite laser communication system under atmospheric fluctuation

Considering the combined effects of the intensity scintillation and the beam wander in the satellite-to-ground laser uplink communication system, the bit error rate (BER) performance of three modulation schemes – on–off keying (OOK), binary phase-shifted keying (BPSK), quadrature phase-shifted keying (QPSK) are investigated. In comparison with the condition in which the atmospheric turbulence is not taken into consideration, conclusions that atmospheric turbulence severely degrades the performance of the system are drawn. Based on the simulation results, the advantages of BPSK are analyzed in contrast with OOK and QPSK. Specially, when transmission power is 4W, performance of OOK shows 18dB impairment while performance of QPSK shows 3dB impairment compared with BPSK under the atmospheric fluctuation. Further compared to QPSK, BPSK owns lower BER and simpler process. Considered the feasibility in communication systems, BPSK should be the most reasonable modulation scheme which can decrease the BER of systems without increasing the transmitter power among these three modulation schemes. Besides, optimum divergence angle, optimum beam radius and appropriate receiver diameter are also analyzed, which is significant in practical applications.

Fast simulation of Strehl loss due to phase aberration for the sizing of adaptive optics in laser communications system design

An approximation is derived for the phase Strehl of an aberrated wavefront based on uncorrelated random variates. Eliminating the requirement to generate correlated variates offers an orders-of-magnitude improvement in simulation speed, while yielding accuracy that may be sufficient for the preliminary sizing of adaptive optics (AO) in laser communications system design. Examples are presented comparing the performance of several AO subsystem sizes when correcting a wavefront aberrated by Kolmogorov turbulence.

Study on Fog Attenuation Characteristics and Experiment Measurement for Laser Propagation in Atmosphere

The availability of atmosphere laser communication systems in dependence on weather conditions and on atmosphere laser link parameters, such as transmitted optical power, beam divergence, or link path distance, is discussed. A number of phenomena in the atmosphere, such as fog, can affect beam attenuation. In this work, the analysis and simulation of the empirical models (like Kruse, Vasseur, etc) indicate that the predicted attenuation of those models is similar and the main attenuation factor of 532nm laser propagation in atmosphere is aerosol particle. Attenuation caused by fog, which can be expressed as a function of the link distance, wavelength, and meteorological visibility, is calculated from visibility data collected at several locations in Guilin. Statistical evaluation of the attenuation caused by fog and the power link margin calculated from atmosphere laser communication link parameters are used for calculating the link availability.