High-Contrast Broadband Optical Edge Detection by Low-Loss Geometric Phase Gratings

Abstract

Optical edge detection is emerging as a key technique in image processing owing to its merits of large-scale and real-time operation. However, achieving both broadband and high-contrast functionality remains challenging. While broadband optical edge detection has been demonstrated using nanograting-based geometric phase (GP) gratings, the relatively low image contrast limits their effectiveness. Here, we demonstrate high-efficiency nanopore-based GP gratings by ultrafast laser writing in silica glass, enabling high-contrast and broadband edge detection. A maximum contrast of 0.97 is achieved at 515 nm, approaching the theoretical limit of unity. We further show that the edge detection contrast and spatial resolution are influenced by the period of the GP gratings. Moreover, the nanopore-based GP gratings exhibit broadband performance from 450 to 2000 nm and support both one-dimensional and two-dimensional edge detection. Finally, we demonstrate edge detection capability in complex environments, e.g., through water or silicon at appropriate wavelengths.