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Quasi-Bragg geometric-phase lens for high-numerical-aperture focusing
Optics Express
|August 14, 2026
Summary
Researchers developed a novel quasi-Bragg geometric-phase lens (QB-GPL) to overcome numerical aperture (NA) limitations in ultrathin optics. This diffraction-regime engineering enables high-NA focusing and imaging in flat optical devices.
Area of Science:
- Optics and Photonics
- Materials Science
- Nanotechnology
Background:
- Geometric-phase lenses (GPLs) offer ultrathin wavefront shaping capabilities.
- A fundamental limitation in numerical aperture (NA) exists for GPLs due to the Raman-Nath diffraction regime.
Purpose of the Study:
- To introduce a quasi-Bragg geometric-phase lens (QB-GPL) that overcomes the NA limitation of traditional GPLs.
- To demonstrate high-NA operation and imaging functionality in a single flat optical device.
Main Methods:
- Spatially engineered the diffraction regime within a single device by combining Raman-Nath and Bragg-like diffraction.
- Utilized a 3D liquid-crystal director distribution formed via contact-transfer exposure.
- Combined a GPL master with an isotropic plano-convex lens to generate a 3D polarization field for Bragg diffraction.
Main Results:
- Finite-difference time-domain simulations predicted near-diffraction-limited focusing.
- Experimental results confirmed high-NA operation and imaging functionality.
- Achieved efficient diffraction under normal incidence in the Bragg-dominant outer region.
Conclusions:
- Diffraction-regime engineering is a powerful design principle for high-performance flat optics.
- The QB-GPL approach overcomes previous NA limitations for ultrathin lenses.
- This work paves the way for advanced flat optical devices with enhanced functionalities.
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