Jianjie Yu

Pointing and tracking errors due to localized deformation in inter-satellite laser communication links

Instead of Zernike polynomials, ellipse Gaussian model is proposed to represent localized wave-front deformation in researching pointing and tracking errors in inter-satellite laser communication links, which can simplify the calculation. It is shown that both pointing and tracking errors depend on the center deepness h, the radiuses a and b, and the distance d of the Gaussian distortion and change regularly as they increase. The maximum peak values of pointing and tracking errors always appear around h=0.2lambda. The influence of localized deformation is up to 0.7microrad for pointing error, and 0.5microrad for tracking error. To reduce the impact of localized deformation on pointing and tracking errors, the machining precision of optical devices, which should be more greater than 0.2?, is proposed. The principle of choosing the optical devices with localized deformation is presented, and the method that adjusts the pointing direction to compensate pointing and tracking errors is given. We hope the results can be used in the design of inter-satellite lasercom systems.

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.

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.

Receiver power penalty due to localized distortion induced by transmission-type optical antenna in inter-satellite laser communications

Based on a truncated ellipse Gaussian model for localized distortion in transmission-type optical antenna, the receiver power penalty due to localized wavefront deformation is researched. It is shown that the receiver power depends on distortion deepness h, radii a and b, and position d, and changes regularly with them. Localized distortion has the greatest influence on receiver power at a depth of h ≈ 1.45λ, which does not depend on other deformation parameters. The maxima of the receiver power penalty for different distortion radii are given. To reduce the impact of localized distortion on the receiver power, the machining precision of lenses should be better than 1.45λ. We hope the results can be used in the design of intersatellite laser communication systems.

Radiation effect on EDFA for inter-satellite optical communication on low dose orbits

The erbium doped fiber, optical isolator and WDM coupler, which are three key optical components of commercial erbium-doped fiber amplifier (EDFA), are radiated to the radiation dose of 5krad by electron. The radiated erbium-doped fiber (EDF) make the output power of EDFA come down 0.5dB when the input power is between -12dBm and-5dBm. The NF climb up 1dB. However, the peak wavelength changes little. The radiation experiment results also show that the deterioration of the optical isolator and WDM coupler can be neglected at the dose of 5krad. In order to assure the accuracy of analysis, the recovery experiment has been done to correct the radiation effect on the EDFA. The results indicate that if optical communication systems have enough redundancy, the EDFA can be used on the low dose orbits without any radiation protection for inter-satellite optical communication.