Spin, Orbital Angular Momentum, and the Shaping of Optical Fields

The control of light has evolved from simple reflective optics to a detailed understanding of electromagnetic waves through Maxwell’s theory. By the early twentieth century, the fundamental equations governing light were established. What became clear later is that light carries not only energy and linear momentum, but also angular momentum in two distinct forms: spin, associated with polarisation, and orbital angular momentum, associated with the spatial structure of the wavefront. These additional degrees of freedom significantly expand the ways in which optical fields can be engineered. Today, structured light plays a central role in both classical photonics and quantum technologies. By tailoring amplitude, phase, and polarisation, one can design beams with nontrivial two- and three-dimensional structures, including optical vortices, polarisation singularities, Möbius-like configurations, and knotted field topologies.

In this talk, I will introduce the physical origin of spin and orbital angular momentum, discuss practical methods for engineering structured optical fields, and explain how these degrees of freedom can be controlled experimentally. I will conclude with two examples demonstrating their use in quantum information science, focusing on high-dimensional quantum communication and photonic quantum simulation.