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Aston University researchers have developed a new class of optical microresonators, miniature optical devices that strongly confine and enhance light in microscopic dimensions. They are essential components in a wide range of systems, including ultra-precise optical sensors and information processors.

The University researchers discovered that unique optical microresonators can be introduced at the intersection of two optical fibers. These devices have potential applications in communication, computing, sensing and more.

The new ultralow loss optical microresonators can be finely tuned by simply rotating two intersecting optical fibers. Unlike current monolithic microresonators, these devices have a widely tunable free spectral range (FSR) and allow for their precise control.

The researchers were led by Professor Misha Sumetsky of Aston Institute of Photonic Technologies. The team's paper "Widely FSR tunable high Q-factor microresonators formed at the intersection of straight optical fibers" has been in the journal Optica.

Professor Sumetsky said, "This geometry opens the door to miniaturized, tunable photonic systems that were previously difficult or impossible to achieve. It is especially promising for applications like low-repetition-rate frequency comb generators, tunable delay lines and nonlocal optofluidic sensors.

"This work was initiated by the experimental discovery of a microresonator at the optical fiber intersection by Dr. Isha Sharma followed by our detailed investigation of their optical properties and tunability.

"Tiny rotation of a fiber by only a fraction of a degree translates to micron-scale fiber displacements, enabling millimeter-scale changes in the resonator geometry and picometer-scale tuning of its spectral and FSR characteristics. The resulting resonators maintain high-Q factors (∼2×10⁶), with the potential to reach ∼10⁸ in cleaner environments."

The research team demonstrated the new microresonators experimentally and supported their findings with theoretical modeling based on the surface nanoscale axial photonics (SNAP) platform.

One notable discovery is the role of van der Waals forces (the forces that attracts neutral molecules to one another) in keeping the fibers in direct contact, contributing to resonator formation over sub-millimeter regions.

Professor Sumetsky added, "The proposed system is ideally suited for micro-electromechanical systems (MEMS) integration, requiring only minimal actuation force to achieve FSR microresonator tunability. By enabling precision spectral control in chip-scale devices, this innovation holds potential across photonics, sensing and quantum information technologies."