Measurements of atmospheric turbulence strength by coherent optical scintillation

Summary The strength of the atmospheric turbulence is measured by an optical scintillation method. The obtained quantity is the structure constant at optical frequencies. As all turbulence parameters, this quantity is strongly affected by meteorological and local conditions, therefore it is of interest to measure it in different conditions and locations. The present measurements were made to characterize the turbulence at Florence. Paper presented at the 1° Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, Rome, June 19–22, 1984.     

Reduction of atmospheric turbulence using optical duplicate system in free-space optical communications

Optical Review - To reduce the effect of atmospheric turbulence and stabilize the optical link in free-space optical (FSO) communications, we have proposed to use an optical duplicate system (ODS)...     

大气闪烁对无线光CDMA通信系统性能的影响

将光CDMA技术应用到无线光通信中。提出了基于脉冲位置调制的二维大气无线光CDMA通信系统，并分析了该通信系统的性能。考虑多用户干扰、APD噪声以及热噪声等干扰因素的影响，采用数值分析的方法，详细分析了大气湍流引起的大气闪烁对二维无线光CDMA通信系统误码率的影响。结果表明，大气闪烁是影响二维无线光CDMA系统误码率性能的一个重要因素；当大气闪烁的对数方差较小(如σ2s=0.1)时，该系统可以实现高速率通信；当大气闪烁的对数方差较大(σ2s≥0.2)时，在有限的光功率条件下，该系统难以实现通信，需要采用信道编码技术来提高系统的误码率性能。     

Polarization-induced reduction in scintillation of optical beams propagating in simulated turbulent atmospheric channels

It is experimentally demonstrated that the class of partially coherent, partially polarized optical beams can be efficiently used for reduction in scintillations on propagation through turbulent air. The experiment involving the electromagnetic beam generation and its interaction with turbulent air simulator is discussed in details. The collected data is in solid agreement with the recently published theoretical predictions.     

Acquisition performance analysis for intersatellite optical communications with vibration influence

A stable and accurate pointing, acquisition system is an important part of initially building intersatellite optical communication links. Satellite platform vibration can cause the system instability and reduce the system precision in building and maintenance of a satellite optical communication system. In this paper, vibration influence is consciously discussed by acquisition time for intersatellite optical communications. Analytical expression of acquisition possibility is derived, taking the scan parameters and platform vibration into account, and vibration influence on the multi-scan acquisition time is also presented. The theoretical result calculated by the proposed analytical expression is approximate to the result by the Monte Carlo simulation.     

Earth-to-deep-space optical communications system with adaptive tilt and scintillation correction by use of near-Earth relay mirrors

Performance of an Earth-to-deep-space optical telecommunications system is degraded by distortion of the beam as it propagates through the turbulent atmosphere. Conventional approaches to correcting distortions, based on natural or artificial guide stars, have practical difficulties or are not adequate for correction of distortions, which are important for Earth-to-deep-space optical links. A beam-relay approach that overcomes these difficulties is discussed. A downward-directed laser near an orbiting relay mirror provides a reference for atmospheric correction. Adaptive optics at the ground station compensate the uplink beam so that after it passes through the atmosphere uplink propagation effects are removed. The orbiting mirror then directs the corrected beam to the distant spacecraft.     

卫星间光通讯中一种光路设计及分析

文中给出了一种卫星间光通讯系统的光路设计，并对影响通讯距离的有关参量进行了分析，找出了提高通讯距离的主要途径     

A sensitivity analysis approach to optical parameters of scintillation detectors

In this study, an extended version of the Monte Carlo light transport code, PHOTRACK, has been used for a sensitivity analysis to estimate the importance of different wavelength-dependent parameters in the modelling of light collection process in scintillators.     

Theoretical analysis of stack gas emission velocity measurement by optical scintillation

Theoretical analysis for an online measurement of the stack gas flow velocity based on the optical scintillation method with a structure of two parallel optical paths is performed. The causes of optical scintillation in a stack are first introduced. Then, the principle of flow velocity measurement and its mathematical expression based on cross correlation of the optical scintillation are presented. The field test results show that the flow velocity measured by the proposed technique in this article is consistent with the value tested by the Pitot tube. It verifies the effectiveness of this method. Finally, by use of the structure function of logarithmic light intensity fluctuations, the theoretical explanation of optical scintillation spec- tral characteristic in low frequency is given. The analysis of the optical scintillation spectrum provides the basis for the measurement of the stack gas flow velocity and particle concentration simultaneously.     

Symbol error rate performance analysis of soft-decision decoded MPPM free space optical system over exponentiated Weibull fading channels

The symbol error rate(SER) performance of a multipulse pulse-position modulation(MPPM) free space optical(FSO) system under the combined effect of turbulence-induced fading modeled by exponentiated Weibull(EW)distribution and pointing errors with a soft-decision detector is investigated systematically. Particularly, the theoretical conditional SER(CSER) of soft-decision decoded MPPM is derived. The corresponding closed-form CSER is obtained via curve fitting with the Levenberg–Marquardt method. The analytical SER expression over the aggregated fading channels is then achieved in terms of Laguerre integration. Monte Carlo simulation results are also offered to corroborate the validity of the proposed SER model.     

Expressions of the scintillation index for optical waves propagating through weak non-Kolmogorov turbulence based on the generalized atmospheric spectral model

The high frequency “bump” which occurs in the turbulence spectral model just prior to the turbulence cell dissipation is important for the analysis of the irradiance scintillation for optical wave propagating through atmospheric turbulence. In this study, expressions of the irradiance scintillation index are developed from the generalized modified atmospheric spectral model for optical waves propagating through weak non-Kolmogorov turbulence. Compared with the expressions of the irradiance scintillation index derived from the general non-Kolmogorov spectral model, the new expressions can consider the influences of finite turbulence inner and outer scales and the influence of finite diameter aperture receiver. As the irradiance scintillation is caused mainly by the small scale turbulence cells' diffractive effects for weak turbulence, the turbulence outer scale's influence can be ignored. Numerical simulations show that variable inner scale values produce obvious effects on the irradiance scintillation for non-Kolmogorov turbulence.     

Design and analysis of the optical transceiver for mobile atmospheric laser communication

The concept of mobile atmospheric laser communication (MALC) is introduced in this paper. Atmospheric attenuation, turbulence-induced scintillation and beam wander cause deep fades in the beam power and degrade the optical channel. The optical transceiver presented in this paper is designed for a MALC test system. Currently achievable hardware performance capabilities for the MALC terminals are used as input parameters to the analysis. A novel optical transceiver structure is designed. Link margin is analyzed using the MALC analysis software, our optical link analysis program. Data rate, bit-error rate, prime transmit     

Analysis of average capacity for free-space optical links with pointing errors over gamma-gamma turbulence channels

<正>A novel closed-form expression for average capacity is derived for free-space optical(FSO) links over Gamma-Gamma turbulence channels by considering the effect of misalignment(pointing errors).The simulation results show that the average capacity of the FSO links can be analyzed with the effects of atmospheric turbulence condition,beam width,detector size,jitter variable,and transmitted optical power. Meanwhile,the results are further provided to verify the accuracy of our mathematical analysis.This work is useful for the FSO designer.     

Generation of multi-wavelength light sources for optical communications in aperiodic optical superlattice

A method for generating multi-wavelength light source is theoretically investigated by optical parametric oscillation (OPO) in aperiodic optical superlattice (AOS). The effects of domain errors caused by the room-temperature electric poling process are checked. The relationship between the linewidth and the block length is also discussed.     

Generation of multi-wavelength light sources for optical communications in aperiodic optical superlattice

A method for generating multi-wavelength light source is theoretically investigated by optical parametric oscillation (OPO) in aperiodic optical superlattice (AOS).     

Fast-processing statistical methods for measurement of BER in optical fiber communication systems

We propose two fast-processing statistical methods for the determination of transmission performance, in particular the eye diagram and BER in optical fiber communication systems. Detailed guidelines for optimizing the accuracies of the statistical techniques are given. These methods provide BERs within one decade, hence more superior than those offered by Monte-Carlo and semi-analytical techniques.     

Feasibility of infrared Earth tracking for deep-space optical communications

Infrared (IR) Earth thermal tracking is a viable option for optical communications to distant planet and outer-planetary missions. However, blurring due to finite receiver aperture size distorts IR Earth images in the presence of Earth's nonuniform thermal emission and limits its applicability. We demonstrate a deconvolution algorithm that can overcome this limitation and reduce the error from blurring to a negligible level. The algorithm is applied successfully to Earth thermal images taken by the Mars Odyssey spacecraft. With the solution to this critical issue, IR Earth tracking is established as a viable means for distant planet and outer-planetary optical communications.     

On-ground simulation of optical links for free-space laser communications

A method of on-ground simulation of optical links for free-space communications by Fourier-transform, image magnification and wavefront sampling with limited apertures was proposed. An optical simulator for free-space laser links was designed, which has the range of equivalent links distances from 160,000 km to 25 km. It can be used for the evaluation of communication performances of optical links in space, particularly for measuring the bit error rate under a constant transmission distance or for testing the equivalent transmission distance under a constant bit error rate. System analysis indicates that the wavefront aberrations of Fourier-transform lens have the main influence on the measurement results. But these effects can be corrected only if the RMS value of wavefront aberrations of Fourier-transform lens on the work aperture is known. Simulation experiment further shows that this method will be feasible by providing excellent optical devices and fine calibration accuracy and by overcoming the environmental disturbances.     

近地层大气光学湍流的分形和间歇性特征分析

利用光纤湍流测量系统获得了合肥西郊科学岛上气象观测场内下垫面平坦的水面上方0.48m、草地上方1.8m和23m高处的大气折射率起伏的观测数据,采用R/S分析法计算了近地层大气光学湍流的赫斯特指数和分形维数,统计分析了分形维数的日变化特征及概率分布特征。结果表明:对于一天的不同时段,分形维数在一定范围内动态变化,且中午时段相对稳定;在三种下垫面条件下,全天分形维数的值大多在1.3~1.4之间,其最可几概率位于1.35处,从均值来看,草地上方1.8m的分形维数最大,水面上方0.48m次之,草地上方23m处最小。最后,初步探讨了近地层大气光学湍流分形维数、间歇性指数和湍流发展程度的相关性。