Sub-kHz lasing of a CaF2 whispering gallery mode resonator stabilized fiber ring laser

We utilize a high quality calcium fluoride whispering-gallery-mode resonator to passively stabilize a simple erbium doped fiber ring laser with an emission frequency of 196 THz (wavelength 1530nm) to an instantaneous linewidth below 650Hz. This corresponds to a relative stability of 3.3 x 10(-12) over 16 mu s. In order to characterize the linewidth we use two identical self-built lasers and a commercial laser to determine the individual lasing linewidth via the three-cornered-hat method. We further show that the lasers are finely tunable throughout the erbium gain region. (C) 2014 Optical Society of America