Wideband ultrafast mode-locked praseodymium- and erbium-doped fiber lasers using zinc phosphate at 1.3- and 1.5 µm

The nonlinear optical behavior of novel zinc phosphate-based saturable absorber (SA) was investigated for the first time in this work. Zinc phosphate was synthesized and coated over an arc-shaped fiber to work as a SA. The zinc phosphate SA was then optically characterized for linear and nonlinear optical absorption. Linear absorption of the zinc phosphate SA was 3.3 dB at 1301 nm and 3.9 dB at 1561 nm. The nonlinear optical analysis of the zinc phosphate SA showed a modulation depth of 18 %. The SA was then incorporated in a praseodymium (Pr³⁺) doped fluoride fiber laser (PDFFL) to achieve stretched pulse mode-locked pulses at 1.3 µm. Ultrashort pulses of 452 fs were obtained from the mode-locked PDFFL with a repetition rate of 0.4 MHz. A high pulse peak power of up to 29.6 kW was obtained at a maximum pump power of 196 mW. Also, incorporating SA in an erbium-doped fiber laser (EDFL) resulted in mode-locked laser operation at 1561 nm. The soliton mode-locked EDFL pulses of 900 fs duration and 19.14 MHz repetition rate were achieved at C-band. These demonstrations validate the wideband saturable absorption of zinc phosphate to generate short pulses in the femtosecond regime.