Chromium oxide film for Q-switched and mode-locked pulse generation

Chromium oxide (Cr₂O₃) is a promising material used in the applications such as photoelectrochemical devices, photocatalysis, magnetic random access memory, and gas sensors. But, its nonlinear optical characteristics and applications in ultrafast optics have not been studied yet. This study prepares a microfiber decorated with a Cr₂O₃ film via magnetron sputtering deposition and examines its nonlinear optical characteristics. The modulation depth and saturation intensity of this device are determined as 12.52% and 0.0176 MW/cm². Meanwhile, the Cr₂O₃-microfiber is applied as a saturable absorber in an Er-doped fiber laser, and stable Q-switching and mode-locking laser pulses are successfully generated. In the Q-switched working state, the highest output power and shortest pulse width are measured as 12.8 mW and 1.385 µs, respectively. The pulse duration of this mode-locked fiber laser is as short as 334 fs, and its signal-to-noise ratio is 65 dB. As far as we know, this is the first illustration of using Cr₂O₃ in ultrafast photonics. The results confirm that Cr₂O₃ is a promising saturable absorber material and significantly extend the scope of saturable absorber materials for innovative fiber laser technologies.