Polymer optical fiber ASE light source and random laser

Abstract

In this thesis, I investigate aspects of Rhodamine 640 (Rh640)-dye-doped polymer optical fiber (POF) with integrated optical cavity formed by gold mirrors on fiber ends, including design, fabrication, and characterization. POF fabrication offers great flexibility in core and cladding structural designs as well as allows incorporation of a wide variety of functional materials. This allows the development of dye-doped POF light sources with specific functions. I also investigate POF with a lightly Rh640-dye-doped core and relatively highly Rh640-dye-doped cladding step-index structure and show that a significant improvement in the emission intensity and photostability is achieved. The latest work has been focused on development of solid core fiber random lasers to experimentally verify some of the published random laser theories, which are still uncertain. I fabricated a solid core POF random laser, with Titanium dioxide (TiO₂) as scatterers and Rh640 dye as gain medium and performed the first demonstration of random lasing in POF. Evenly distributed discrete narrow random lasing peaks with peak linewidth of 0.5nm and peak separation of 0.9nm in emission spectrum are observed. A systematic experimental investigation of random laser with various densities of scatterer has been carried out. After optimization of scatterer density, single-mode POF random lasing is achieved for 20ppm TiO₂ ~400nm diameter), POF core diameter of 400nm, with scattering mean free path = 11.9mm. Since the modes of a random laser are sensitive to the scatterers, we may use the random laser as a sensor for anything that modifies the scattering characteristics of the medium. Therefore, the study of the effect of perturbation made to the lasing mechanism of random fiber laser and the associated emission spectra characteristics is proposed for future work.