Ultra-high quality factor and polarization-sensitive Γ-point unidirectional guided resonances.

Area of Science:

• Photonics
• Materials Science
• Nanotechnology

Background:

• Photonic crystals (PhCs) offer unique light manipulation properties.
• Unidirectional guided resonances (UGRs) are key for efficient light outcoupling and polarization control.
• Silicon-on-lithium niobate (Si-on-LN) platforms are promising for integrated photonics.

Purpose of the Study:

• To systematically analyze the quality (Q) factors and polarization characteristics of UGRs in a symmetry-broken Si-on-LN PhC slab.
• To demonstrate ultra-high Q-factor UGRs and broadband polarization conversion.
• To explore the tunability of UGRs via structural asymmetry.

Main Methods:

• Numerical simulations of a symmetry-broken Si-on-LN PhC slab.
• Analysis of UGRs at the Γ-point.
• Optimization of structural asymmetry parameters.
• Investigation of polarization conversion efficiency and bandwidth.

Main Results:

• Achieved ultra-high Q-factor UGRs at the Γ-point through controlled asymmetry.
• Demonstrated flexible tuning of UGR Q-factors from 10³ to 10⁶.
• Obtained broadband high-efficiency linear-to-circular polarization conversion (>99.5% over 20.5 nm).

Conclusions:

• Controlled asymmetry in Si-on-LN PhC slabs enables ultra-high Q-factor UGRs.
• UGRs facilitate efficient and stable broadband polarization conversion.
• The findings support applications in lasers, optical phased arrays, and spectroscopy.