Study on optical coupling characteristics of a high-radial-tolerance thick-lens beam expanding fiber collimator

Abstract

In this paper, a high-radial-tolerance fiber collimator (HRTFC) consisting of beam expanding fiber (BEF) and thick-lens (T-lens) is designed. The HRTFC uses BEF to reduce coupling loss, while T-lens are used to increase the outgoing spot to enhance the tolerance of radial mismatch. Firstly, the Gaussian beam ABCD optical transmission matrix is used to analyze transmission properties of light in the T-lens. Then, a beam transmission coupling model is constructed to explore the coupling losses of radial, angular, and axial mismatches under different spots. Finally, a static experimental platform is built to verify the influence of spot size on the coupling mismatch, and a dynamic experimental platform is built to monitor the temperature without contact. The experimental results show that the coupling loss decreases from 1.808 dB to 0.368 dB in the HRTFC, with the fiber mode field diameter (MFD) increasing from 10μm to 28μm. Increasing the spot of the HRTFC to a certain extent can reduce the tolerance of angular mismatch but can significantly increase the tolerance of radial mismatch.