Whispering Gallery Mode Resonator Stabilized Narrow Linewidth Fiber Loop   Laser
  We demonstrate a narrow line, fiber loop laser using Erbium-doped fiber as the gain material, stabilized by using a microsphere as a transmissive frequency selective element. Stable lasing with a linewidth of 170 kHz is observed, limited by the experimental spectral resolution. A linear increase in output power and a red-shift of the lasing mode were also observed with increasing pump power. Its potential application is also discussed. 
B. Sprenger, H. G. L. Schwefel, and L. J. Wang
physics.optics