Ultrafast Modulation of Guided‐Mode Resonance in a Nonlinear Silicon Nitride Grating

Abstract Nonlinear optical interactions in nanostructures are crucial for both fundamental research and practical applications. The optical Kerr effect, a third‐order nonlinear phenomenon, causes anisotropic changes in the refractive index of materials under intense laser illumination. However, this effect is intrinsically weak, limiting its utility in free‐space nanophotonics. This work demonstrates an enhancement of the optical Kerr effect by over three orders of magnitude through guided‐mode resonance in a dielectric diffraction grating with a thickness of less than 300 nm. The study includes the design, fabrication, and transmittance measurements of a resonant silicon nitride crossed grating, illuminated with short light pulses. Spectral resonance shifts with increasing pulse power are observed, resulting in over 50% modulation of the resonance magnitude and enabling dynamic transitions between “Off ” and “On” transmission states of the grating. Additionally, the potential of the grating for dynamic pulse shaping is demonstrated. These findings offer promising avenues for developing advanced all‐optical devices in free‐space nanophotonics.