Broadband nonlinear optical modulator enabled by VO₂/V₂O₅ core-shell heterostructures

Broadband pulsed lasers have become an indispensable part in optical communications, biomedical engineering, materials processing, and national defense. Inspired by the broadband and ultrafast optical components, great efforts from the laser and material community have been paid to explore the emerging nonlinear optical materials. Here, we found that the VO₂/V₂O₅ core-shell heterostructures with type-II staggered band alignment exhibit broadband nonlinear optical response towards mid-infrared spectral range. The nonlinear optical characterizations verify that the heterostructures show the modulation depth and saturation intensity of 27% and 42 GW/cm² at 1064 nm, 23% and 78 GW/cm² at 1550 nm, and 16.5% and 63.9 GW/cm² at 2800 nm, respectively. With the nonlinear optical modulator, stable mode-locked Yb-doped and Er-doped fiber lasers have been realized with pulse output as short as 310 ps and 633 fs, respectively. In addition, the stable Q-switched Er-doped fluoride fiber laser has been demonstrated with a pulse repetition rate of 89 kHz and the shortest pulse width of 680 ns, respectively. The experimental results indicate that VO₂/V₂O₅ core-shell heterostructures can be broadband nonlinear optical modulators from the near-infrared to the mid-infrared spectral range, offering opportunities to develop high-performance photonic devices.