Enhanced optical edge detection based on a Pancharatnam–Berry flat lens with a large focal length
Ting Li, Yang Yang, Xinyang Liu, Yan Wu, Yuan Zhou, Sijia Huang, Xiaochun Li, Huihui Huang
Abstract
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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>2</mml:mn> <mml:mspace width="thinmathspace"/> <mml:mspace width="thinmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mtext>µ</mml:mtext> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> </mml:mrow> </mml:mrow> </mml:math> 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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>></mml:mo> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>90</mml:mn> </mml:mrow> </mml:mrow> <mml:mi mathvariant="normal">%</mml:mi> </mml:math> ). 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.