In a recent study published in Light: Science & Applications, a team of scientists led by Prof. Lixin Guo from Xidian University expressed their insights on the history and future of optical metrology using orbital angular momentum (OAM). The study delves into fundamental ideas, applications, and significant developments in the field.
Conceptual notion of twisted light probing a complex medium. An artistic illustration of twisted OAM light passing through a medium, where the OAM spectrum acts as a sensor to monitor its effects. The signature can be read out and analyzed using machine learning and AI algorithms to recognize or sense key features of the medium, as exemplified in the context of a turbulent atmosphere. Image Credit: Mingjian Cheng, Wenjie Jiang, Lixin Guo, Jiangting Li, and Andrew Forbes
Metrology is the foundation of modern industry, giving the primary standards by which we measure the world. Optical metrology, in particular, has historically relied on the concept of interference, which has remained largely intact since the time of Thomas Young over 200 years ago. Can one learn more by applying the concept of fringes to other degrees of freedom?
The researchers show how twisted light carrying OAM can be utilized for novel measurement paradigms, such as 3D particle position tracking, using a modern interpretation of the Doppler effect to see frequency shifts that are dependent on both OAM and polarization.
The original Doppler effect could only track movement toward or away from the observer, but the incorporation of orbital angular momentum in both scalar and vector light allows motion tracking in all directions, including rotational movement. This advancement has revolutionized the metrology of dynamic systems.
Andrew Forbes, Study Corresponding Author and Professor, University of the Witwatersrand
The field is being propelled forward by a paradigm change in existing tools and the development of whole new instruments. One such example is the concept of an OAM spectrum acting as a system’s ‘signature’: as OAM light passes through a complex medium, its OAM is altered, causing changes in the form of the OAM spectrum.
Dr. Mingjian Cheng, the lead author, added, “This OAM fingerprint of the medium contains a wealth of information that can be harnessed.”
According to the review, interpreting the OAM spectrum with machine learning and AI paves the way for real-time analysis and recognition of complex material, with OAM light serving as a probe, a rapidly growing field.
The review discusses metrology using classical light as well as the use of OAM in quantum entangled superpositions and single-photon states. Transitioning to the quantum realm has the ability to minimize noise while increasing accuracy and precision with fewer observations. However, this element of the subject is still in the early phases of development.
Forbes added, “Quantum metrology using OAM is still an emerging field with numerous untapped opportunities.”
The comprehensive review covers a wide spectrum of applications, from small nanosensing to cosmic black hole measurements. It presents an authoritative summary that will benefit both new and seasoned scholars.
Journal Reference:
Cheng, M., et. al. (2025) PMetrology with a twist: probing and sensing with vortex light. Light: Science & Applications. doi.org/10.1038/s41377-024-01665-1