Passively Harmonic Mode-Locked Fiber Laser With a High Signal-to-Noise Ratio via Evanescent-Light Deposition of Bismuth Telluride $(\hbox{Bi}_{2}\hbox{Te}_{3} )$ Topological Insulator Based Saturable Absorber

Passively harmonic mode locking (HML) operation had been demonstrated in an erbium-doped fiber laser with a microfiber-based topological insulator (TI) Bi
₂
Te
₃
saturable absorber (SA). It was found that the pulse train possessed different orders of HML (with a tunable repetition rate from 232 to 390 MHz) due to different incident pump powers. The spectra exhibited typical features of conventional solitons (perfect Gaussian profile with Kelly sidebands) with no continuous wave component. The measured signal-to-noise ratio (SNR) reached 60 dB, whereas the pulse duration was kept around 1.32 ps without significant change. The experimental observation revealed that the microfiber-based TI device could indeed be employed as a high-performance SA for further applications in ultrafast photonics.