High-efficiency diffractive waveguide lenses by parametric optimization

Area of Science:

• Optics
• Photonics
• Materials Science

Background:

• Waveguide diffraction gratings are crucial optical components.
• Optimizing their diffraction efficiency is key for advanced photonic devices.
• Effective-index modulation is a critical parameter influencing grating performance.

Purpose of the Study:

• To maximize the first-order diffraction efficiency of waveguide diffraction gratings.
• To investigate the impact of effective-index modulation profiles on grating performance.
• To apply optimized grating designs to diffractive waveguide lenses.

Main Methods:

• Thin-grating-decomposition method for analysis.
• Optimization of effective-index modulation profiles.
• Verification using electromagnetic grating theory.

Main Results:

• Maximum diffraction efficiency achieved through optimized effective-index modulation.
• Optimized lens structure approximates a gradient-thickness Fresnel lens near the optical axis.
• Deviations from Fresnel structure observed for grating periods below ~15-25λ, forming Bragg gratings at ~3-6λ.

Conclusions:

• Effective-index modulation optimization is vital for high-efficiency waveguide gratings.
• Optimized gratings enable improved diffractive waveguide lenses.
• The study reveals structural transitions in gratings based on local period and wavelength.