Investigation of optical coupling characteristics in a single-mode elliptical core step-index fiber integrated with a cylindrical microlens under mechanical offset conditions

We provide a rigorous study of an optical coupling configuration comprising a laser diode (LD), a single-mode elliptical core step-index fiber (SMECSIF), and a cylindrical microlens (CML) integrated onto the fiber end. Both angular and lateral misalignments are methodically included in the analysis to evaluate their effect on coupling performance. Gaussian approximations are adopted for the optical fields of the laser source and the guided fiber mode, enabling the formulation of a simple but reliable analytical model for estimating coupling efficiency (CE) under specified misalignment conditions. The optical transformation introduced by the CML is modeled using the ABCD matrix approach within the paraxial regime, with explicit consideration of finite-aperture effects. Investigations are carried out at the two significant wavelengths, 1.3 µm and 1.5 µm. Three distinct elliptical core step-index fibers are examined, each characterized by an identical normalized frequency ( V = 1.4) but differing in geometry of the core. The proposed framework requires minimal computational effort and clearly elucidates the sensitivity of coupling efficiency to mechanical offsets. The outcomes offer practical insights for the design of such coupling system having less sensitivity in respect of the said offsets.