L-band dual wavelength passively Q-switched erbium-doped fiber laser based on tellurium oxide nanoparticle saturable absorber

We experimentally demonstrate a compact dual wavelength passive Q-switched fiber laser created by an erbium-doped fiber active medium using tellurium oxide nanoparticles (TeO2 NPs) as a new saturable absorber (SA) material. The saturable absorption properties of the prepared TeO2-PVA thin film were systematically measured, and the modulation depth and saturation intensity were 8% and 90 MW cm(-2), respectively. By integrating the proposed SA in an all-fiber ring cavity, a dual wavelength laser with 1568.02 and 1569.09 nm wavelengths was observed without adding spectral filters or polarization maintaining fibers to control the suppression of the mode competition. A frequency difference of 0.13 THz was obtained located in the terahertz waveband. In the meantime, a stable Q-switched regime with a maximal pulse repetition rate of 45.7 kHz, a shortest pulse width of 2.69 mu s and maximum pulse energy up to 39.4 nJ was attained at a maximum available pump power of 275 mW. The experimental setup using the TeO2 NP SA represents a step forward in terahertz development and nonlinear optics.