Enhanced optical edge detection based on a Pancharatnam-Berry flat lens with a large focal length

In this Letter, we employ photo-aligned liquid crystals to record a flat lens pattern through a simple exposure method to produce a large focal length Pancharatnam-Berry (PB) lens with a film thickness of 2µm without using expensive equipment. This PB lens with a focal length of 240.6 m (at 532 nm) can transmit up to 97% across visible wavelengths and maintain high diffraction efficiency (>90%). An improved two-dimensional optical edge detection design based on this lens is proposed. We experimentally demonstrate the integrity and high efficiency of edge information that may play an important role in the application of image processing and high-contrast microscopy.