Passively Q-switched erbium all-fiber lasers by use of thulium-doped saturable-absorber fibers

We demonstrate all-fiber passively Q-switched erbium lasers at 1570 nm using Tm³⁺-doped saturable-absorber fibers. The absorption cross section of a Tm³⁺-doped fiber at 1570 nm was measured in a bleaching experiment to be about 1.44 × 10^-20 cm². With a thulium-doped fiber, sequential pulses with a pulse energy of 9 μJ and a pulse duration of about 420 ns were stably produced at repetition rates in the range 0.1 to 2 kHz. The maximum pulse repetition rate was 6 kHz, limited by the maximum pump power of a 980-nm laser diode, about 230 mW.