Analysis of efficiency and misalignment tolerances in laser diode pigtailing using single ball lens

Abstract

In this paper we present some investigations and analysis on coupling efficiency and misalignment tolerances in coupling of laser diode to single mode fiber using single ball lens of (diameter = 1mm, and refractive index n = 1.8333). It has been found that there should be an optimization for positioning of the ball lens between laser diode and the tip of the fiber. At some optimum positions, the cupping efficiency can reach maximum value over 90% when the ratio of the divergence angles x y (M = è / è ) in both x and y directions respectively is (20/33) and the mode matching is very effective as it is illustrated by the effect of the lateral and angular offsets in both x and y directions on the misalignment tolerances. But when the ratio is (M=8/33) there is a reduction in coupling efficiency and the transformation is not effective. We also studied the effect of the transformed beam waist radii on the 1_dB axial, lateral and angular misalignment tolerances for the proposed coupling scheme and also noticed that the mode matching is very effective for (M=20/33). Our experimental results showed a significant relaxation in misalignment tolerances using single ball lens for coupling with optimum coupling efficiency of about 55% at a relaxed working distance in the range of (0.7 – 1.2 mm).