Broadband optical and microwave nonlinear response in topological insulator

We experimentally studied the nonlinear response of topological insulator (TI): Bi2Te3 at both the optical and microwave band, and found that the absorbance of topological insulator decreases with the increase of the incident power and reaches at a constant value once the incident power exceeds a threshold. By the open-aperture Z-scan and balanced twin detector measurement techniques, the optical saturable absorption property of TI: Bi2Te3 from 800 nm to 1550 nm was experimentally demonstrated. Based on a power dependent microwave transmittance experimental setup, TI: Bi2Te3 was also identified to show a saturation intensity of ~12 μW/cm2 and a normalized modulation depth of ~70%. We argue that the optical (resp. microwave) saturable absorption in topological insulator is a natural consequence of the Pauli-blocking principle of the electrons filled in the bulk insulating state (resp. surface metallic state). Our experimental results illustrate the potential photonic applications of TI: Bi2Te3 at both the optical and microwave band.