Patent ID: 7106762

Claim:
A fiber laser, comprising: A gain fiber less than 5 cm in length including, A core formed from a glass host selected from germanate, tellurite or fluoride, said glass host being doped with 0.5–15 wt. % of thulium or holmium oxide or mixtures thereof; and A cladding formed from the same glass host; A narrowband grating having a linewidth and a broadband grating at opposite ends of the fiber that define an optical resonant cavity; and A source of pump radiation that illuminates the fiber to excite the dopant ions and provide gain; the length of the resonant cavity producing a mode spacing that is comparable with the narrowband grating's linewidth so that the dopant ions lase at a single longitudinal mode, said fiber laser outputting a single-frequency signal having a center wavelength between approximately 1.8 μm and 2.1 μm with a linewidth less than 100 kHz.