Research Of Single-mode Fiber Coupling Based On Adaptive Fiber Coupler

Coupling plane wave into single mode fiber (SMF) is a key technique in free space opticalcommunication (FSO) using fiber devices. The average efficiency and stability of SMF couplingdrop with quasi-static angular errors induced by gravity and temperature variation, randomangular jitters caused by the oscillation of laser transmission and reception platform, andatmospheric turbulences varied in real-time. Adaptive fiber coupler (AFC) is a kind of adaptivefiber device which can compensate tip-tilt errors to improve SMF coupling efficiency byadaptively controlling the tip of the fiber end. This dissertation mainly researches the SMFcoupling efficiency in the presence of quasi-static angular errors, random angular jitters andatmospheric turbulences and the effects of AFC and adaptive fiber coupler array (AFCA) incompensating aberrations and increasing coupling efficiency. The main contents include:The theoretical formulas of SMF coupling efficiency are derived using mode-matchingprinciple without and with quasi-static angular errors, random angular jitters and atmosphericturbulence. The impacts of atmospheric turbulence and effects of compensating tip-tilt errors onSMF coupling are simulated using Matlab software. SMF coupling efficiency decreases sharplywith quasi-static angular errors and random angular jitters, which means that these errors must becorrected. Satisfying SMF coupling efficiency could be achieved by correcting only tip-tilt errorsof atmospheric turbulence when the ratio of D/r0is small, while both tip-tilt and high order errorsshould be compensated when D/r0is big, where D is the aperture of the optical receiver and r0isthe spatial coherence distance.Experimental setup of SMF coupling with tip-tilt error compensation using AFC isestablished, and experiments of SMF coupling by correcting quasi-static angular errors, randomangular jitters and simulated turbulences are completed. The results show that, the efficiency andstability of SMF coupling are both improved when quasi-static angular errors, random angularjitters and simulated turbulences are corrected using AFC, and the correctness of the simulatedanalysis above are proved.A new concept of fiber coupling with AFCA is presented to compensate atmosphericturbulence and improve coupling efficiency of optical receiver in the case of big D/r0. Thismethod is realized by correcting tip-tilt errors and enhancing SMF coupling efficiency in eachsub-aperture of AFCA. An AFCA-based coupling model is built with numerical simulation to study the effect of AFCA in improving coupling efficiency of optical receiver and the influence ofsub-aperture number and fill factor of AFCA on coupling efficiency. A real AFCA with fill factorof0.875and a kind of six-dimension adjustment unit for AFC are also developed.It is confirmed through theory, simulation and experiment that, the AFC and AFCA areefficient to compensate quasi-static angular errors, random angular jitters and atmosphericturbulence, and to improve the efficiency and stability of fiber coupling of optical receiver inFSO.