Qingbo Yang

Statistical model of the efficiency for spatial light coupling into a single-mode fiber in the presence of atmospheric turbulence.

The average efficiency of spatial light coupling into a single-mode optical fiber is widely used but cannot estimate the signal-to-noise ratio (SNR) and bit error rate (BER) in free-space optical communication. We provide a statistical model for coupling efficiency and derive the exact expression of the probability density function (PDF). The simulation results confirm that the model is reasonable in the condition of different turbulence intensities and wavefront compensation terms, which is also consistent with our outdoor experiment. We also estimate the average SNR and BER using the PDF. The model is quite useful in a satellite-to-ground laser communication downlink.

Fiber-coupling efficiency of Gaussian Schell model for optical communication through atmospheric turbulence

In practice, due to the laser device and the inevitable error of the processing technique, the laser source emitted from the communication terminal is partially coherent, and is represented as a Gaussian Schell model (GSM). The cross-spectral density function based on the Gaussian model in previous research is replaced by the GSM. Thus the fiber-coupling efficiency equation of the GSM laser source through atmospheric turbulence is deduced. The GSM equation presents the effect of the source coherent parameter ζ on the fiber-coupling efficiency, which was not included previously. The effects of the source coherent parameter ζ on the spatial coherent radius and the fiber-coupling efficiency through atmospheric turbulence are numerically simulated and analyzed. The result manifests that the fiber-coupling efficiency invariably degrades with increasing ζ. The work in this paper is aimed to improve the redundancy design of fiber-coupling receiver systems by analyzing the fiber-coupling efficiency with the source coherent parameters.

Research on real time detection of departure angle for the laser beam through atmospheric channels

The precision of departure angle detection for the laser beam can be improved by optimizing algorithms by which the high precision and stability of the laser beam pointing and tracking would be obtained, namely, improving the performance and accommodation of the free space optical communications. Atmospheric turbulence-induced optical intensity scintillations have a strong impact on the location precision of the laser spot through the atmospheric channels. Consequently, new requests come into view for the optimization of the algorithms. In the paper, the advantages and disadvantages of the traditional centroid method are analyzed. In terms of variations of laser spot, combined with the requests for real-time detection of departure angle, we proposed a new detection method. The edge of the laser spot on the detection sensor was redefined, and then the redefined spot was used to calculate the departure angle of the laser beam. The results of the simulations and experiments show that the precision of departure angle detection has been improved by more than 16%, which could reduce the effect of detection errors on the tracking procedure.

Statistical distribution of the optical intensity obtained using a Gaussian Schell model for space-to-ground link laser communications

Abstract Based on the characteristics of the laser device and the inevitable error of the processing technique, a laser beam emitted from a communication terminal can be represented by the Gaussian Schell model (GSM). In space-to-ground link laser communications, the optical intensity is affected by the source coherence parameter and the zenith angle. With full consideration of these two parameters, the statistical distribution model of the optical intensity with a GSM laser in both downlink and uplink is derived. The simulation results indicate that increasing the source coherence parameter has an effect on the statistical distribution of the optical intensity; this effect is highly similar to the effect of a larger zenith angle. The optical intensity invariably degrades with increasing source coherence parameter or zenith angle. The results of this work can promote the improvement of the redundancy design of a laser communication receiver system.

Experimental investigation of gamma ray radiation effects on 1550nm single mode fiber

We compared the degradation of two kinds of 1550nm single-mode optical fibers following the irradiation by gamma ray (60Co). Over a total dose of 9.06×104 rad, the absorption coefficient increased while the rates were different between samples. The influence of ionizing radiation is theoretically analyzed. In room temperature annealing experiment, the absorption coefficient of Corning sample was recovered visibly, but Alcatel sample continues to deteriorate. It is suggested that different producing technology and doping are clearly influence the generation and recombination process of color center.

Influence of aberrations of receiver antenna on heterodyne efficiency in free-space optical communications based on heterodyne detection

Heterodyne efficiency in free-space optical communications based on heterodyne detection is degraded by the aberrations of the optics antenna used for reception of optical beams. The evolution of heterodyne efficiency with the change of rms of primary aberrations is investigated. It is shown that heterodyne efficiency decreases gradually with increasing primary aberrations. The comparison shows that different aberration types have variant influence on heterodyne efficiency. In addition, obscuration ratio of receiver antenna has a noticeable but relatively minor influence on heterodyne efficiency. We hope this work can benefit system design of heterodyne receiver in free-space coherent communications.