Dual-wavelength, cascaded cavities bismuth-doped fiber laser in 1.7 μm wavelength range

A comprehensive theoretical investigation of a dual wavelength, cascade cavity bismuth-doped fiber (BDF) laser operating in the wavelength range of 1.7μm is presented. The fiber laser model is based on parameters extracted from experimental characterization of the BDF. The BDF serves as an active medium with optical gain in the wavelength region from 1.65μm to 1.8μm. The laser cavity is defined by a 90% mirror on one end of the BDF and two fiber Bragg gratings (FBG1 and FBG2) separated with the BDF on the other end of the laser cavity. One of the gratings FBG1 with the peak reflectivity 95% is centered at 1.725μm. The second one FBG2 with peak reflectivity of 90% is centered at 1.729μm. Both FBGs have a 3-dB bandwidth of ~0.5nm. It is shown that the cascade laser can operate at two 1.725μm and 1.729μm wavelengths with different powers depending on the parameters of the structure.