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

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.