Yijun Jiang

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.

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.

Temporal-frequency spectra for optical wave propagating through non-Kolmogorov turbulence

Nowadays it has been accepted that the Kolmogorov model is not the only possible turbulent one in the atmosphere, which has been confirmed by the increasing experimental evidences and some results of theoretical investigation. This has prompted the scientist community to study optical propagation in non-Kolmogorov atmospheric turbulence. In this paper, using a non-Kolmogorov power spectrum which has a more general power law instead of standard Kolmogorov power law value 11/3 and a more general amplitude factor instead of constant value 0.033, the temporal power spectra of the presentative amplitude and phase effects, irradiance and angle of arrival fluctuations, have been derived for horizontal link in weak turbulence. And then the influence of spectral power-law variations on the temporal power spectrum has been analyzed. It is anticipated that this work is helpful to the investigations of atmospheric turbulence and optical wave propagation in the atmospheric turbulence.

Approach to improve beam quality of inter-satellite optical communication system based on diffractive optical elements

For inter-satellite optical communication transmitter with reflective telescope of two-mirrors on axis, a large mount of the transmitted energy will be blocked by central obscuration of the secondary mirror. In this paper, a novel scheme based on diffractive optical element (DOE) is introduced to avoid it. This scheme includes one diffractive beam shaper and another diffractive phase corrector, which can diffract the obscured part of transmitted beam into the domain unobscured by the secondary mirror. The proposed approach is firstly researched with a fixed obscuration ratio of 1/4. Numerical simulation shows that the emission efficiency of new figuration is 99.99%; the beam divergence from the novel inter-satellite optical communication transmitter is unchanged; and the peak intensity of receiver plane is increased about 31% compared with the typical configuration. Then the intensy patterns of receiver plane are analyzed with various obscuration ratio, the corresponding numerical modelling reveals that the intensity patterns with various obscuration ratio are nearly identical, but the amplify of relative peak intensity is getting down with the growth of obscuration ratio. This work can improve the beam quality of inter-satellite optical communication system without affecting any other functionality.

A novel approach for simulating the optical misalignment caused by satellite platform vibration in the ground test of satellite optical communication systems

Satellite platform vibration causes the misalignment between incident direction of the beacon and optical axis of the satellite optical communication system, which also leads to the instability of the laser link and reduces the precision of the system. So how to simulate the satellite platform vibration is a very important work in the ground test of satellite optical communication systems. In general, a vibration device is used for simulating the satellite platform vibration, but the simulation effect is not ideal because of the limited randomness. An approach is reasonable, which uses a natural random process for simulating the satellite platform vibration. In this paper, we discuss feasibility of the concept that the effect of angle of arrival fluctuation is taken as an effective simulation of satellite platform vibration in the ground test of the satellite optical communication system. Spectrum characteristic of satellite platform vibration is introduced, referring to the model used by the European Space Agency (ESA) in the SILEX program and that given by National Aeronautics and Space Development Agency (NASDA) of Japan. Spectrum characteristic of angle of arrival fluctuation is analyzed based on the measured data from an 11.16km bi-directional free space laser transmission experiment. Spectrum characteristic of these two effects is compared. The results show that spectra of these two effects have similar variation trend with the variation of frequency and feasibility of the concept is proved by the comparison results. At last the procedure of this method is proposed, which uses the power spectra of angle of arrival fluctuation to simulate that of the satellite platform vibration. The new approach is good for the ground test of satellite optical communication systems.

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.

Comparison between two algorithms of angle departure detection for the Free Space Optical Communications

The image of a beacon on the photosensitive plane of pointing sensor in a receiving terminal is usually considered as the acquisition and tracking target of optical antenna for the Free Space Optical Communications (FSOC). The receiver processes the acquired image to ascertain the position of the transmitting terminal by the relevant algorithm. The tracking veracity of the algorithm to a target position is not the same under different conditions. Improving the algorithm veracity could improve the tracking accuracy of optical antenna and guarantee the optical link stabilization. In the paper we proposed that the acquisition position should be ascertained based on the geometric centroid for terrestrial FSOC in the city. Based on the experiment of terrestrial long haul optical link, we analyzed the tracking veracity of the centroid and geometric centroid algorithms for the stationary and locomotory targets under different intensity scintillations. A comparison of the two algorithms is also studied. The results show that the geometric centroid algorithm on ascertaining the acquisition position is superior to the centroid algorithm. This work contributes to the design of FSOC systems.