Abstract

In this work, a novel continuous wave fiber laser, pumped at ${\lambda }_p = 1550\ \text{nm}$ and emitting at ${\lambda }_s = 4\ \mu \text{m}$ , has been designed and optimized. It is based on a step-index, double-cladding, praseodymium-doped fluoroindate glass fiber, available on market, having dopant concentration ${N}_{Pr} = 8000\ \text{ppm}$ . For a realistic design, measured spectroscopical parameters have been taken into account, writing a five-level rate equation model. The design is carried out by employing a homemade code solver. The best predicted slope efficiency of about $\eta = 33{{ \% }}$ and pump power threshold ${P}_{th} = 0.007\ \text{W}$ have been obtained for a fiber length ${L}_{fiber} = 0.4\ \text{m}$ and output mirror reflectivity ${R}_{out} = 30\% $ . These values are very interesting with reference to the state of the art and promise the fabrication of high beam quality optical sources in the middle infrared range, by employing conventional erbium-doped fiber pumping lasers, with a potentially easy all-in-fiber integration.