Self-Assembled Topological Insulator: Bi $_{2}$ Se $_{3}$ Membrane as a Passive Q-Switcher in an Erbiu

We demonstrate a new type of optical saturable absorber based on the self-assembled topological insulator Bi₂Se₃ membrane fabricated by the drop-cast/evaporation approach. The strong viscosity of Bi₂Se₃ allows its attachment onto the optical fiber end-facet for practical optoelectronic applications. The balanced twin-detector technique was used to characterize the saturable absorption parameters of the device, which has a saturating intensity of 101.8 MW/cm² and a modulation depth of 41.2% at the telecommunication band. By deploying this device into a fiber laser cavity, we had achieved stable Q-switched pulses with a repetition rate of 8 kHz and pulse duration of 14 μs. Through fine tuning the laser pump strength and/or cavity birefringence, we could widely change the Q-switched pulse repetition rate from 4.508 kHz to 12.88 kHz, pulse duration from 13.4 μs to 36 μs, and lasing wavelength from 1545.0 nm to 1565.1 nm. A dual-wavelength passive Q-switching operation was also obtained by enhancing the intra-cavity birefringence. Our results show the effectiveness of developing Bi₂Se₃ optical saturable absorber device by the drop-cast/evaporation method and applications for pulsed laser operation.