Theoretical and experimental analysis of polymer optical fibers working as broadband lasers

The Variable Stripe Length (VSL) method is applied to side-pumped rhodamine 6G-doped gradedindex polymer optical fibers (POFs) of two different dopant concentrations. For each position of the blocking blade, we obtain the output powers that serve to determine the net optical gain per unit length (g) of each pumped fiber, and we analyze the corresponding output spectral widths and average wavelengths. The study, which is carried out both theoretically and computationally, provides an insight into the effect of the dopant concentration on the emission properties of POFs working as broadband lasers. For a fixed concentration and pump energy, greater gains g are achieved with shorter excitation lengths, i.e. with greater intensities. For a fixed excitation length and pump energy, a blue shift and a spectral narrowing of the emission spectra transmitted by the fiber have been observed as the concentration increases, irrespective of the total fiber length. The same occurs when the excitation length is increased.