Ce-doped fiber as a gain material for visible laser sources

Abstract

In the quest for efficient and compact visible laser sources, fiber lasers have emerged as promising candidates due to their advantages in applications such as telecommunications, medical diagnostics, laser displays, and material processing. Developing suitable gain materials is critical for enhancing the performance and versatility of these lasers. While Cerium (Ce) doped materials have been successfully utilized in solid-state lasers, their application in fiber laser technology remains largely unexplored. The unique properties of Ce, associated with 5d to 4f electronic transitions, offer broad emission across the visible to near-infrared range, making it a promising candidate for expanding the capabilities of fiber lasers. Such source directly emitted in the visible wavelength range can become an affordable alternative to cumbersome supercontinuum sources.

This thesis investigates the potential of Ce-doped silica fibers as an active medium for visible laser sources. The study involves the characterization of Ce-doped fibers fabricated using modified chemical vapor deposition (MCVD) technology. Eight fibers samples with varying doping concentrations, core diameters, and refractive index profiles were evaluated. Key optical properties such as luminescence, attenuation, bending loss, and beam profile were characterized. The cut-back method was used as a characterization technique for the attenuation measurements. The measurements revealed broad emission spectra ranging from approximately 450 nm to 800 nm, peaking near 484 nm, and broad absorption features in the UV to visible regions, indicating areas where losses such as re-absorption and background loss could affect the fibers' performance. Bending loss and beam profile analyses were conducted to understand the wave guidance of the fibers and identify the source of losses. The results indicate that factors such as doping concentration and the properties of the host material significantly influence the fibers' luminescence characteristics and loss mechanisms. These results highlight the fibers’ potential as gain media, while also indicating areas where improvements are needed.

To address these challenges, further efforts are needed to enhance absorption efficiency, fine-tune the pump wavelength, and optimize Ce ion concentration to boost luminescence without introducing additional losses. This research provides a foundation for advancing Ce-doped fibers as promising gain materials for visible laser applications, potentially opening new paths in fiber laser design.