Metrology, the science of measurement, underpins modern industry, offering the standards that define how we measure the world. At its core, optical metrology relies on interference fringes — the alternating light and dark bands that appear when light waves interact constructively and destructively. This fundamental principle has remained largely unchanged since Thomas Young’s double-slit experiments over 200 years ago. But could the concept of fringes be extended to new dimensions of measurement?
The classic double-slit interference pattern remains foundational to modern optical metrology, as researchers now extend these principles to orbital angular momentum-based measurements for multidimensional sensing and analysis” Image by Graham Beards – Own work, CC BY-SA 4.0.
A recent paper published in Light: Science & Applications explores this question. Led by Prof. Lixin Guo of Xidian University, the paper delves into the evolving field of optical metrology involving orbital angular momentum (OAM). It examines foundational principles, transforming advancements, and novel applications of OAM-based measurement. The researchers highlight how twisted light, which carries OAM, unlocks new paradigms, such as tracking 3D particle positions and analyzing frequency shifts influenced by OAM and polarization — a modern take on the Doppler effect.
“The original Doppler effect could only track movement toward or away from the observer, but incorporating 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, in Newswise.
The paradigm shift extends to developing entirely new instruments, including the OAM spectrum — a system’s ‘signature.’ When OAM light passes through a complex medium, it alters the OAM, reshaping its spectrum (See Figure 1 in the Nature article).
“This OAM fingerprint of the medium contains a wealth of information that can be harnessed,” explains Dr. Mingjian Cheng, the paper’s lead author. The review suggests that combining OAM spectrum data with machine learning and AI could enable real-time analysis and recognition of complex media using OAM light as a probe, a rapidly advancing area of study.
The review also addresses metrology with classical light and explores the potential of OAM in quantum systems, including quantum-entangled superpositions and single-photon states. Transitioning to the quantum domain could reduce noise and enhance measurement accuracy with fewer samples, though this area remains nascent.
“Quantum metrology using OAM is still an emerging field with numerous untapped opportunities,” says Prof. Forbes.
Applications of OAM-based metrology span scales from nano sensing at the microscopic level, probing cosmic phenomena like black holes, and perhaps contributing to next-generation semiconductor electronics. The paper provides a thorough overview, offering valuable insights for newcomers and seasoned field researchers.
