Femtosecond harmonic mode-locking of a fiber laser based on a bulk-structured Bi₂Te₃ topological insulator

We experimentally demonstrate femtosecond harmonic mode-locking of a fiber laser using a bulk-structured Bi₂Te₃ topological insulator (TI)-deposited on a side-polished fiber as a mode-locker. A bulk-structured Bi₂Te₃ TI film was prepared at a thickness of ∼20 μm using a mechanical exfoliation method. Using the mode-locker in an erbium-doped fiber ring cavity, it was experimentally shown that harmonically mode-locked pulses with temporal widths of 630 ∼700 fs could readily be generated upto the 55th harmonics. The pulse repetition rate was shown to be tunable from the fundamental resonance frequency of 14.07 MHz to the harmonic frequency of 773.85 MHz with increasing pump power. The pumping efficiency was measured at ∼3.36 MHz/mW. The side mode suppression ratio (SMSR) was observed to be more than 27.3 dB over all harmonic orders, while the corresponding signal-to-noise ratio (SNR) ranged from 46.3 to 63 dB.