Wavelength Extension of Er-Doped Fluoride Fiber Laser to Above 3800 nm

We report the first demonstration of Er-doped ZBLAN fiber laser operating above 3800 nm. Numerical modeling is carried out to optimize the cavity arrangement for laser gain improvement at long wavelength, based on which 0.74 W laser output at 3803 nm is experimentally obtained, with a slope efficiency (with respect to the incident 1990 nm pump power) of 9.5%. Experimental observation shows that the gain competition at the 3.5-mu m emission peak of the gain fiber is the main obstacle for long-wavelength operation. By reducing the cavity loss to suppress the gain competition, the emission wavelength is further extended to 3810 nm. The corresponding laser wavelength behavior is well explained through the analysis of laser threshold under different cavity loss. Further power scaling and wavelength extension are also discussed based on the modeling, which reveals the potential to generate ten-watt-level output power at 3800-3810 nm by using an optimized all-fiber scheme.