Research On Fiber Coupling With Spatial Light Incident Offset In Satellite Communication Terminal

Satellite optical communication has many advantages than microwave communication, such as larger capacity of communication, higher communication rate et al., so the satellite optical communication technology has been highly valued. In order to improving the detection sensitivity, realizing the high-speed data rate of satellite laser communication system, and under the condition of considering engineering implementation difficulty, combining the ground optical fiber communication optical amplifiers with WDM technology becomes a potential option. In such a system, coupling the space beam to single- mode optical fiber becomes the first technical problems to be solved.In the process of coupling the space light into single mode fiber, the coupling efficiency is very sensitive to the alignment error. The coupling efficiency reduc ing can lead to the decrease of the optical receiver sensitivity, and keep ing low alignment error requires that the tracking precision of optical communication system must be put forward higher requirements, so improving the fiber coupling tolerance features for optical communication system is necessary. Based on the status of fiber coupling tolerance is small, the coupling characteristic is optimized, the main research works are as follows:Firstly, the development of satellite optical communications is introduced, both domestic and foreign research progress in single- mode fiber coupling are discussed. Based on the model of space light to single-mode fiber coupling, using the theory of mode coupling, the coupling efficiency expression is deduced in the best case. Providing coupling efficiency correction factor in case of the lateral, axial and tilt deviation, analyzed the influence of lateral deviation on the coupling efficiency. The equivalence of incidence Angle deviation and the transverse displacement deviation affects on coupling efficiency is analyzed.Secondly, the defocus field of coupling lens is analyzed, the axial deviation factor’s influence on the coupling parameter is discussed. The changes of characteristic parameter with different coupling parameters are studied. Reducing the coupling parameters can improve the deviation tolerance of coupling system. Based on the Code V, the coupling system is set up, then the simulation test and verify are carried out.Finally, based on the tapered fiber, the coupling characteristics and the multimode to single mode conversion are studied. The transmission principle of tapered optical fiber is introduced, and the geometrical parameters are analyzed. Tapered optical fiber transmission characteristics are analyzed by using local mode theory, the ABCD matrix of Gaussian beam transmission in Tapered fiber is deduced, mode field change of the conical end is analyzed, and the simulation of optical waveguide transmission has been done in this paper, the change process of the optical field distribution is stated. Light field Gaussian approximation is used to calculate the tapered optical fiber transmission efficiency. A self- made tapered fiber has been carried on the experiment that coupled spatial light to multimode optical fiber, and the power transferred though the tapered optical fiber, then got the coupling efficiency. The use of tapered fiber for space optical coupling, compared with the single mode fiber coupling, has better system deviation tolerance.