Analysis of fiber lens with gradient index based on thin lens equivalence

Abstract

Theoretical analysis of the fiber-lens TEC (Thermally Expended Core)/Coreless/GRIN (Graded-Index) based on thin lens equivalence is presented in this paper. On condition that the TEC part adjusts the waist radius of an incident Gaussian beam, that the coreless part controlls the space between the beam waist and the thin lens, and that the GRIN part acts as the thin lens with its focal length determined by fiber index distribution parametereg, the analytic expressions of the waist spot size and the working distance of the output Gaussian beam are derived, and the influence of the coreless fiber and the length of the GRIN fiber upon the fiber-lens parameter is discussed based on the numerical simulation results. It is concluded that, if a GRIN style fiber-lens is used as a collimator, the maximum of the spot waist can be up to 80 μm and the divergence angle of single-mode optical fiber can be reduced by 8 times. If it is applied to a MEMS device, the maximum working distance can be up to 3 mm.

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