Ultrafast fiber laser based on bismuth telluride evanescent field mode-locked device

In order to realize the passively harmonic mode-locking with high repetition rate in the fiber laser. A saturable absorber (SA) based on two dimensional (2D) topological insulators material of Bismuth telluride (Bi₂Te₃), combining with a side-polished fiber, was fabricated by laser deposition technology in this study. This device has a modulation depth of 23.96%, nonsaturable loss of 37.77% and saturable intensity of 31.5 MW/cm². According to the adjustment of dispersion in the whole cavity and the excellent nonlinear saturable absorb character in topological insulator materials, a self-starting mode-locking is realized successfully when this SA device is applied in the Er-doped fiber laser, with a central wavelength of 1555.67 nm, pulse duration of 487 fs, repetition rate of 47.87 MHz and signal-to-noise ratio of 58 dB. A harmonic mode-locking is achieved when the pump power is over 150 mW. When we adjust and increase slightly the pump power till 250 mW, the harmonic mode-locking of 11 orders is achieved with the repetition rate of 528 MHz and the signal-to-noise ratio of 41.5 dB. These results demonstrate that with the evanescent field produced by the side-polished fiber, the damage threshold of materials can be improved and the passively harmonic mode-locking with high repetition rate is realized, which has a great significance for the materials in the application of ultrafast fiber laser with high repetition rate.