Intrapulse multimodal four-wave sum mixing in the visible range from high contrast index grating with PMMA layer

Area of Science:

• Nanophotonics
• Metasurface Optics
• Nonlinear Optics

Background:

• Nonlinear metasurfaces offer nanoscale control over light-matter interactions.
• Frequency conversion is crucial for compact photonic devices.
• High-index contrast gratings (HCGs) can support unique optical resonances.

Purpose of the Study:

• To experimentally observe and theoretically analyze intrapulse four-wave sum mixing (FWSM).
• To investigate FWSM in a silicon-based HCG supporting quasi-bound states in the continuum (q-BIC) and guided-mode resonances (GMR).
• To demonstrate tailored nonlinear frequency mixing using coupled resonances.

Main Methods:

• Fabrication of a 1D silicon HCG with a PMMA cladding layer.
• Simultaneous excitation of q-BIC and GMR modes.
• Broadband femtosecond laser excitation.
• Fourier microscopy measurements.

Main Results:

• Observation of multiple distinct spectral peaks in the visible range due to FWSM.
• Evidence of nonlinear coupling between q-BIC and GMR modes.
• Confirmation of nonlinear signal redistribution among diffraction orders via Fourier microscopy.

Conclusions:

• Demonstrated a novel approach for nonlinear frequency mixing using metasurfaces.
• Leveraged the interaction of multiple non-local resonances (q-BIC and GMR).
• Opened new pathways for tunable frequency conversion, all-optical signal processing, and nonlinear photonic devices.