Highly efficient one- and two-cascade Raman lasers based on phosphosilicate fibers

Abstract

Characteristics of one-cascade (1.06 ⇒ 1.24 µ m) and two-cascade (1.06 ⇒ 1.24 ⇒ 1.48 µ m) phos- phorus-doped fiber Raman lasers are studied. The cavities of both lasers are formed by Bragg gratings written directly in the active fiber. Double-cladding Yb 3+ and Nd 3+ ion fiber lasers with λ ~ 1.06 µ m were employed for pumping. These lasers were pumped, in their turn, by diode laser arrays with λ ~ 0.98 µ m (Yb) and λ ~ 0.81 µ m (Nd). The efficiency of the one-cascade laser with an unprecedentedly short length of 50 m was as high as 65% with 4.8-W pump radiation applied to the input of the laser. The maximum efficiency of the two-cascade Raman fiber laser was 40%. Gratings directly written in the active fiber reduced concentrated losses in laser cavities, which allowed the laser length to be decreased and the lasing threshold power of Raman fiber lasers to be low- ered.