Numerical design on blue diode pumping of deep-red lasers in Ho3+/Tb3+ co-doped fluoride fibers

In this study, the performance of a continuous-wave (CW) deep-red Ho³⁺/Tb³⁺ co-doped fluoride fiber laser was numerically investigated. The laser operated at approximately 750 nm and was cladding pumped by a blue diode. The laser slope efficiency is studied and discussed in relation to the effects of fiber length, output mirror reflectivity, and pump wavelength. The results indicate that Tb³⁺ ions can assist the Ho³⁺: ⁵F₄ + ⁵S₂→⁵I₇ transition in overcoming the population inversion bottleneck, resulting in a significant increase in efficiency and power scalability. At a launched pump power of 60 W, the calculated CW output power of 30.86 W was associated with a slope efficiency of 52%. Such a result encourages the development of a deep-red laser that is constructed from a fluoride fiber co-doped with Ho³⁺ and Tb³⁺.