Optical metrology has long relied on interference principles, but a recent review highlights how orbital angular momentum (OAM) is redefining the field.
By integrating OAM into metrological tools, researchers are now capable of tracking motion in all directions, including rotational dynamics.
Advancing Optical Metrology with Orbital Angular Momentum
Metrology is the foundation of modern industry, providing the essential standards for measuring the world around us. Optical metrology, in particular, has long relied on the principle of interference — a concept largely unchanged since Thomas Young’s groundbreaking experiments over 200 years ago. But what if this concept could be expanded to explore entirely new dimensions of measurement?
In a recent study published in Light: Science & Applications, a research team led by Prof. Lixin Guo from Xidian University examines the evolution and future potential of optical metrology using orbital angular momentum (OAM). The paper highlights fundamental principles, key applications, and major advancements in the field. The researchers showcase how twisted light carrying OAM can unlock innovative measurement techniques, such as 3D particle tracking, by leveraging a modern interpretation of the Doppler effect, which accounts for frequency shifts influenced by both OAM and polarization.
Revolutionizing Dynamic Systems with Twisted Light
“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,” says Prof. Andrew Forbes, a corresponding author from South Africa. “This advancement has revolutionized the metrology of dynamic systems.”
It is not only the shift in paradigm for existing tools but also the invention of completely new instruments that is propelling the field forward. One such example is the concept of an OAM spectrum serving as the ‘signature’ of a system: when OAM light passes through a complex medium, its OAM is altered, resulting in changes to the shape of the OAM spectrum (see Figure 1).
Machine Learning and AI in OAM Spectrum Analysis
“This OAM fingerprint of the medium contains a wealth of information that can be harnessed,” says Dr. Mingjian Cheng, the lead author. As the review highlights, if the OAM spectrum is interpreted by machine learning and AI, it opens the door to real-time analysis and recognition of complex media, with OAM light serving as a probe, a topic that is gaining traction very fast.
The review not only covers metrology with classical light but also utilizing OAM in quantum entangled superpositions and single-photon states. Transitioning into the quantum domain holds the potential to reduce noise and enhance accuracy and precision with fewer measurements. However, this aspect of the field remains in its early stages of development.
“Quantum metrology using OAM is still an emerging field with numerous untapped opportunities,” says Prof. Andrew Forbes.
Applications from the Microscopic to the Cosmic Scale
The comprehensive review spans a wide range of applications, from nano-sensing at the microscopic scale to measuring black holes at the cosmic scale. It provides an authoritative overview that will prove invaluable to both entry level and experienced researchers alike.
Reference: “Metrology with a twist: probing and sensing with vortex light” by Mingjian Cheng, Wenjie Jiang, Lixin Guo, Jiangting Li and Andrew Forbes, 32 December 2024, Light: Science & Applications.
DOI: 10.1038/s41377-024-01665-1
