Wavelength-tunable mode-locked laser using zinc phosphate as a saturable absorber at 1.9 μm

Metal phosphates have emerged as low-cost inorganic materials suitable for high-performance energy storage and conversion devices. The photoluminescence properties of metal phosphates are now being explored for their optoelectronic applications. Among them, zinc phosphate is the composition of metal zinc and phosphoric acid. In this work, we have demonstrated the synthesis of zinc phosphate by the solvothermal method and its potential as a saturable absorber (SA) to generate a tunable mode-locked laser at 1.9 μ m. Zinc phosphate was coated over arc-shaped fiber and incorporated in a thulium-holmium doped fiber laser (THDFL) to achieve the mode-locking. Soliton mode-locked pulses were achieved at a center wavelength of 1893 nm with the pulse duration, repetition rate, and signal-to-noise ratio (SNR) of 1.12 ps, 12 MHz, and 68 dB, respectively. The center wavelength of the mode-locked laser was tunable from 1893 to 1898.4 nm, and the pulse duration ranged between 1.12 to 1.4 ps. To the authors’ knowledge, this is the first demonstration of a wavelength-tunable mode-locked laser using zinc phosphate as a SA at 1.9 μ m.