Abstract
Structured light with inhomogeneous phase, amplitude, and polarization spatial distributions that represent an infinite-dimensional space of eigenstates for light as the ideal carrier can provide a structured combination of photonic spin and orbital angular momentum (OAM). Photonic spin angular momentum (SAM) interactions with matter have long been studied, whereas the photonic OAM has only recently been discovered, receiving attention in the past three decades. Although controlling polarization (i.e., SAM) alone can provide useful information about the media with which the light interacts, light fields carrying both OAM and SAM may provide additional information, permitting new sensing mechanisms and light–matter interactions. We summarize recent developments in controlling photonic angular momentum (AM) using complex structured optical fields. Arbitrarily oriented photonic SAM and OAM states may be generated through careful engineering of the spatial and temporal structures of optical fields. Moreover, we discuss potential applications of specifically engineered photonic AM states in optical tweezers, directional coupling, and optical information transmission and processing.
Highlights
Light is a viable information carrier employing the various forms of light–matter interactions for numerous applications in data transmission, optical communications, photonics, and optoelectronics
spin angular momentum (SAM) causes a microscopic object to spin around its own axis, while orbital angular momentum (OAM) causes the particle to revolve around the beam axis, owing to the rotational torque transferred from angular momentum (AM) of the light to these objects.[19,99,100]
Recent theoretical and experimental studies show the existence of transverse optical OAM in both free space and localized fields
Summary
Light is a viable information carrier employing the various forms of light–matter interactions for numerous applications in data transmission, optical communications, photonics, and optoelectronics. Through introducing a helical phase in the spatiotemporal domain, the spatiotemporal optical vortex (STOV) can be generated, which carries OAM perpendicular to the beam propagation direction.[60,61,62] Using a method similar to the conversion from the Hermite–Gaussian mode to the Laguerre–Gaussian mode with a cylindrical lens in the spatial domain, subwavelength focused STOV can be created through preconditioning both phase and amplitude distributions of the incident wave packet, paving the way for the study of transverse OAM with nanostructures and materials.[63]. With the rapid advances in nanofabrication and optical field engineering, arbitrarily oriented photonic SAM and OAM states can be generated by customizing spatially and spatiotemporally structured light. Typical applications of engineered photonic AM states will be discussed, and future perspectives for this very nascent field will be presented
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