Cavity-Q-driven phenomena in an evanescent-wave pumped and gain coupled whispering-gallery-mode fiber laser

We study cavity-Q-driven lasing wavelength shift and line-width widening in an evanescent-wave pumped and gain coupled Whispering-Gallery-Mode (WGM) fiber lasers. A bare optical fiber is immersed in a lower refractive index (RI) dye solution, pumped and gain coupled by evanescence waves, and linearly polarized WGM lasing emission is observed from the rim of the fiber. We find that both lasing wavelengths and line width of WGM peaks are sensitive to the RI of the dye solution and the fiber diameter, with the increase of the RI of the dye solution or decrease of the fiber diameter, a blue shift of the lasing spectrum and a widening on the spectral line width are observed. The observed phenomena have been attributed to the change of quality factor of a circular cavity built in the fiber cross section, the achieved experimental data agree well with the calculated values of the quality factor.