Analysis of contributing factors in coupling from laser diode into optical fiber

In this paper, the impacts of contributing factors which affect the coupling efficiency between LD (laser diode) and MMF (multi-mode fiber) are studied. The coupling principle is presented and the characteristic parameters of the optical components such as laser source beam size, focal length of lens and numerical aperture (NA) of both LD and optical fiber are analyzed to derive their influence on the coupling efficiency. Another main source causing the coupling loss is the misalignment during adjusting and fixing the position of fiber, referring to the axial, lateral and angular misalignment error. According to the actual characteristics of these factors, a coupling system from LD to fiber is established and related experiments are conducted to confirm these impacts and optimize the parameters of the optical components by theoretical calculation, simulation and experiments. The tolerance ranges of the factors mentioned above are respectively evaluated quantitatively as a strict coupling loss limit less than 1dB is demanded. In conclusion the modulating precision we work out proves to be within several microns, all the analysis results provide an essential guidance in coupling scheme designing for a better improvement of coupling efficiency in further experiments and applications.