Encoding orbital angular momentum of light in space with optical catastrophes

TL;DR

This paper introduces a method to encode and control the orbital angular momentum of light beams in space using optical caustics shaped by metasurfaces, enabling advanced applications in secure communication and optical manipulation.

Contribution

It presents a novel approach to tailor OAM across multiple planes with optical caustics and metasurfaces, allowing dynamic, intrinsic OAM control for secure and versatile optical applications.

Findings

Successfully shaped OAM beams with complex caustics

Achieved hidden OAM along propagation for secure encoding

Demonstrated intrinsic OAM detection for encryption

Abstract

Light beams carrying orbital angular momentum (OAM) possess an unbounded set of orthogonal modes, offering significant potential for optical communication and security. However, exploiting OAM beams in space has been hindered by the lack of a versatile design toolkit. Here, we demonstrate a strategy to tailor OAM across multiple transverse planes by shaping optical caustics leveraging on catastrophe theory. With complex-amplitude metasurfaces fabricated using two-photon polymerization lithography, we construct these caustics to steer Poynting vectors and achieve arbitrary shapes of OAM beams. Interestingly, we use such an approach to realize hidden OAM along the propagation trajectory, where the intensity of the beam is spread out thus avoiding detection. The OAM of these beams can be intrinsic, which avoids OAM distortions arising from the mixing of intrinsic and extrinsic components. By exploiting this intrinsic nature of OAM, we demonstrate the detection of encoded information in optical encryption. Our approach provides a unique framework for dynamic control of OAM in space, with promising applications in optical trapping and sensing, high-capacity data storage, and optical information security.