Theoretical and experimental study on optical coupling features for vertical cavity surface emitting lasers

This thesis investigates methods to enhance the coupling properties between 850 nm Vertical-Cavity Surface-Emitting Lasers (VCSELs) and Standard Single-Mode Fibers (SSMFs), a critical challenge in the development of low-cost and energy efficient Radio-over-Fiber (RoF) communication systems. The study comprises three main components: a thorough analysis of VCSEL operating principles and characteristics, the development of a flexible MATLAB-based simulation tool to evaluate VCSEL-to-fiber coupling under various conditions, and the experimental assessment of an innovative polymer-based tapered beam-shaper structure designed to improve optical coupling efficiency. The thesis first provides a detailed overview of VCSEL technology, highlighting its advantages such as low power consumption, efficient beam characteristics and compatibility with photonics integration, thus positioning VCSELs as an ideal candidate for "green" RoF systems. Subsequently, a robust numerical simulation model was created that allowed comprehensive exploration and optimization of coupling scenarios by taking into account critical parameters such as fiber alignment and angular tilts. Although the simulated results showed some discrepancies when compared with experimental data, the overall coupling trends and behavior were successfully validated, establishing the tool as reliable and useful for future system optimization. Finally, the study experimentally evaluated a polymer-based tapered beam shaper developed by ICON Photonics. The device demonstrated its effectiveness in reshaping the emitted VCSEL beam, significantly reducing divergence and improving coupling efficiency. Despite practical challenges related to precise alignment and handling, the promising performance of the beam shaper indicated its potential as a superior alternative to conventional butt-coupling techniques.