Highly Efficient and Robust Broadband Nano-VO2(M) Saturable Absorber for Nonlinear Optics and Ultrafast Photonics

The metal-to-insulator transition behavior and the fast and reversible phase transition behavior in vanadium dioxide (VO2) have attracted widespread attention to study various potential applications. However, few studies have been focused on its nonlinear properties and applications in the pulsed laser field. Here, the authors report the design and synthesis of monoclinic nano-VO2(M) saturable absorber with broadband absorption which spans the entire near-infrared region, and high optical nonlinearity which is much higher than those of carbon nanomaterials, gold nanocrystals, and Cu1.8S nanocrystals, as measured in the same condition. The nano-VO2(M) optical modulators are integrated into the fiber laser cavities, and demonstrate wideband Q-switching operations at 1, 1.56, and 2 mu m and mode-locking operation at 2 mu m, with a pulse duration of 765 fs. This work first reveals the outstanding nonlinear optical properties of nano-VO2(M) and lays a foundation for its development in advanced nonlinear optical and photonic devices.