Launch optics in case of single-mode elliptical core step-index fiber with cylindrical microlens on its tip

Abstract This article presents a comprehensive theoretical analysis of the performance of a coupler system consisting of a laser diode (LD) and a single-mode elliptical core step index fiber (SMECSIF), together with a cylindrical microlens (CML) fabricated on the fiber tip. The study employs Gaussian field distributions for both the laser source and the fiber mode to develop a simplified yet accurate model for predicting the coupling efficiency (CE) between the LD and the SMECSIF through the CML. The analysis utilizes the ABCD matrix formalism under the paraxial approximation in order to describe the optical behaviour of the CML and explicitly accounts for the effect of its finite aperture. Analytical expressions for the CE are derived, allowing simple evaluation without the need for complex numerical simulations. The model developed helps to study the different parameters of fibers and source wavelengths in order to maximise the coupling performance. This analysis is therefore beneficial for providing theoretical guidance on designing efficient and high performance LD to fiber coupling systems.