Siyuan Yu

Log-amplitude variance for a Gaussian-beam wave propagating through non-Kolmogorov turbulence

In the past decades, both the increasing experimental evidences and some results of theoretical investigation on non-Kolmogorov turbulence have been reported. This has prompted the study of optical propagation in non-Kolmogorov atmospheric turbulence. In this paper, using a non-Kolmogorov power spectrum which owns a generalized power law instead of standard Kolmogorov power law value 11/3 and a generalized amplitude factor instead of constant value 0.033, the log-amplitude variances for a Gaussian-beam wave are derived in the weak-fluctuation regime for a horizontal path. The analytic expressions are obtained and then used to analyze the effect of spectral power-law variations on the log-amplitude fluctuations of Gaussian-beam wave.

Influence of beam wander on bit-error rate in a ground-to-satellite laser uplink communication system

Based on weak fluctuation theory and the beam-wander model, the bit-error rate of a ground-to-satellite laser uplink communication system is analyzed, in comparison with the condition in which beam wander is not taken into account. Considering the combined effect of scintillation and beam wander, optimum divergence angle and transmitter beam radius for a communication system are researched. Numerical results show that both of them increase with the increment of total link margin and transmitted wavelength. This work can benefit the ground-to-satellite laser uplink communication system design.

Experimental investigation of radiation effect on erbium-ytterbium co-doped fiber amplifier for space optical communication in low-dose radiation environment

High power erbium-ytterbium co-doped fiber amplifier (EYDFA) has been radiated to the dose of 50 krad at the dose rate of 40 rad/s. Some key parameters have been measured to investigate the radiation effect on the EYDFA for space optical communication. Considering the dose of 50 krad is big enough to the most of low-dose radiation environment, these experimental results will be a good reference for the low-dose inter-satellite optical communication designers.

Measurement of optical intensity fluctuation over an 11.8 km turbulent path

An 11.8km optical link is established to examine the intensity fluctuation of the laser beam transmission through atmosphere turbulence. Probability density function, fade statistic, and high-frequency spectrum are researched based on the analysis of the experimental data collected in each season of a year, including both weak and strong fluctuation cases. Finally, the daily variation curve of scintillation index is given, compared with the variation of refractive-index structure parameter C(n) (2), which is calculated from the experimental data of angle of arrival. This work provides the experimental results that are helpful to the atmospheric propagation research and the free-space optical communication system design.

Investigation of the irradiation effect on erbium-doped fiber amplifiers composed by different density erbium-doped fibers

Two erbium-doped fibers (EDFs) with different densities, which can make the erbium-doped fiber amplifier (EDFA) achieve the same output power, have been irradiated by 60Co at the same rate and same total dose. In addition, the irradiation effect on EDFA composed by different density EDFs is firstly analyzed in this paper. The experimental results indicate that, considering the length of EDF, the high density EDF can make the EDFA deteriorate less than the low that in the irradiation environment. Furthermore, the small change of the central wavelength and the half-wave width also confirm that the irradiation effect on EDFA chiefly introduces the transmission loss, but the physical mechanics of EDFA is not changed by the irradiation. The experimental results and conclusions will be a good reference for EDFA designers who are trying to apply the EDFA in an irradiation environment.

Performance analysis of satellite-to-ground downlink coherent optical communications with spatial diversity over Gamma-Gamma atmospheric turbulence.

The performances of satellite-to-ground downlink optical communications over Gamma-Gamma distributed atmospheric turbulence are studied for a coherent detection receiving system with spatial diversity. Maximum ratio combining (MRC) and selection combining (SC) techniques are considered as practical schemes to mitigate the atmospheric turbulence. Bit-error rate (BER) performances for binary phase-shift keying modulated coherent detection and outage probabilities are analyzed and compared for SC diversity using analytical results and for MRC diversity through an approximation method with different numbers of receiving aperture each with the same aperture area. To show the net diversity gain of a multiple aperture receiver system, BER performances and outage probabilities of MRC and SC multiple aperture receiver systems are compared with a single monolithic aperture with the same total aperture area (same total average incident optical power) for satellite-to-ground downlink optical communications. All the numerical results are verified by Monte-Carlo simulations.

Analytical expression and optimization of spatial acquisition for intersatellite optical communications

In intersatellite optical communications it is important to obtain the most efficient performance of acquisition system with respect to acquisition time for a given probability. In this paper a novel approach to the analytical optimization of spatial acquisition is presented as an alternative of the conventional Monte Carlo simulation. First, an analytical expression of estimating mean acquisition time (MAT) is derived as a function of the desired acquisition probability, taking into account the distribution function of satellite position, field of uncertainty (FOU), beam divergence angle and dwell time. Accordingly, the analytical expression of multi-scan, which is always adopted by practical optical terminals to ensure the acquisition success, is also presented. Then, by minimizing the MAT of multi-scan, the optimum ratio of the FOU θU to the pointing error deviation σis obtained, which is θU/σ=1.3. An example for a practical intersatellite acquisition between a Low Earth Orbit Satellite and a Geostationary Earth Orbit Satellite is given. And the theoretical result calculated by the proposed analytical expression is approximately equal to the result by Monte Carlo simulation. The results can be used in designing acquisition system for the intersatellite optical communications.

Plane wave coupling into single-mode fiber in the presence of random angular jitter

Efficient coupling of coherent plane waves into single-mode fibers is a key technology for free-space optical communication at 1550 nm. Here we deal with the influence of random angular jitter on a plane wave to single-mode fiber coupling. The expression of mean-coupling efficiency in the presence of random jitter is handled in the pupil plane. First, an analytical expression of the mean-coupling efficiency is derived for the zero bias error case. Then the bias error was taken into account. By minimizing the coupling efficiency penalty, the optimum value of design parameter beta of fiber-coupled optical systems in the presence of random jitter is obtained. The results obtained here will be useful in facilitating parametric estimation and optimization of fiber-coupled optical systems.

Temporal power spectrum of irradiance fluctuations for a Gaussian-beam wave propagating through non-Kolmogorov turbulence

In the past decades, both the increasing experimental evidence and some results of theoretical investigation on non-Kolmogorov turbulence have been reported. This has prompted the study of optical propagation in non-Kolmogorov atmospheric turbulence. In this paper, based on the thin phase screen model and a non-Kolmogorov power spectrum which owns a generalized power law instead of standard Kolmogorov power law value 11/3 and a generalized amplitude factor instead of constant value 0.033, the temporal power spectrum of irradiance fluctuations for a Gaussian-beam wave is derived in the weak fluctuation regime for a horizontal path. The analytic expressions are obtained and then used to analyze the influence of spectral power law variations on the temporal power spectrum of irradiance fluctuations.

Electron radiation effects on InAs/GaAs quantum dot lasers

The InAs/GaAs quantum dot laser diodes and corresponding quantum dot samples are irradiated by 1 MeV electron. The laser performance and quantum dot photoluminescence intensity at room temperature are enhanced over a fluence range of 4 × 1013 cm−2. The radiation-induced defects increase the efficiency of carrier transfer to the quantum dots, which results in the improvement of photoluminescence performance under low level displacement damage. The contact resistant of quantum dot lasers decreases because the ohmic contact is also improved by electron irradiation.