Modeling and experimental characterization of a dual-wavelength Bi-doped fiber laser with cascaded cavities

We present a comprehensive theoretical and experimental investigation of a dual-wavelength, bismuth-doped fiber (BDF) laser operating near 1700 nm based on cascaded cavities. The BDF provides optical gain from 1650 nm to 1800 nm when pumped at 1550 nm. The linear laser cavity is defined by a 90% fiber mirror on one end and two fiber Bragg gratings (FBGs) with two lengths of BDF in cascade on the other. The laser can operate at either wavelength alone, or both wavelengths simultaneously by simple adjustment of the pump power. We develop a model based on rate equations and radiation transport equations for two level BDF lasers which we then extend to the case for cascaded cavities. Experimental results agree with simulations.