All-Optical Switching of Two Continuous Waves in Few Layer Bismuthene Based on Spatial Cross-Phase Modulation

Bismuthene, the last and heaviest group-VA elemental two-dimensional material, has received tremendous interests owing to its advantages in electronic-transport, semimetallic bonding, and intrinsic spin-orbit coupling. However, light-bismuthene interaction is relatively less investigated. Herein, sonochemical exfoliation approach had been employed to deliver a successful synthesis of few-layer bismuthene with an average thickness of similar to 3nm and a lateral size of similar to 0.2 mu m. The corresponding band structure from mono to sextuple-layer had been therotically calculated and it was found that bismuthene possesses a thickness dependent energy gap from almost zero to 0.55 eV, suggesting that bismuthene may also find unique applications from terahertz, mid-infrared toward infrared regime. The nonlinear optical absorption and refraction parameters had been well characterized by laser Z-scan and spatial phase modulation measurement techniques, respectively. By taking advantage of its strong nonlinear refraction effect, all optical switching of two different laser beams based on spatial cross-phase modulation had been eventually realized. It is further found that a modulated signal light clearly observed as switch light is turned on. The achievement of all optical switching suggests that the bismuthene-based 2D material is indeed an excellent candidate for an all optical switcher. Particularly, the semimetallic and long-term stable property in few layer bismuthene make it as a promising nonlinear optical material for infrared and mid infrared optoelectronics. Our work demonstrates a large potential of this new material for nonlinear photonics and this contribution may provide new photonics avenue toward bismuthene-based devices (such as broadband detector, nonlinear optical switcher, phase modulator, etc.).