Cascade lasing optimization in Dy-doped ZBLAN fiber lasers for efficient yellow emission

The interest in Fiber Lasers (FLs) operating in the yellow range of the visible spectrum has greatly increased alongside the improvement of blue GaN pump laser diodes, as well as the recent fabrication of high-quality Dysprosium (Dy) doped fluoride fibers, to be used as active medium [1,2]. Even though alternative yellow sources are available, FLs are cost-effective, compact, and efficient solutions that can provide advantages for applications in many fields (biomedicine, ophthalmology, spectroscopy, etc.) [1]. The 4F9/2 → 6H13/2 transition of Dy3+ ions has already been exploited to experimentally demonstrate different types of yellow FLs via pumping at around 450 nm, the slope-efficiency of which is negatively affected by signal excited state absorption from the lower laser level. Recently, cascade lasing at 3 µm through the 6H13/2 → 6H15/2 transition was proposed to mitigate this effect [2]. However, a thorough numerical analysis of cascade lasing providing key information for design optimization of yellow fiber-based sources is not available in literature.