Theoretical and experimental investigation of a resonantly pumped thulium doped fluorozirconate fiber amplifier at around 810 nm

The potential of thulium-doped fluorozirconate fibers to provide an efficient AlGaAs diode pumped traveling wave amplifier at wavelengths around 810 nm is investigated. The authors present calculations and experimental measurements of the small signal gain when excitation is resonant with the upper laser level, with a view to predicting the upper limits of performance for optimized fiber design. The theoretical treatment involves numerical determination of the evolution of pump and signal power (and hence gain) along the length of the fiber as a function of wavelength, spectral lineshapes and lifetimes, and geometrical factors. Amplification over the range 800-830 nm has been achieved in multimoded fiber with a best observed gain of 22 dB at 806 nm