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Researchers have developed a theoretical framework for creating tunable microresonators using intersecting optical fibers through surface nanoscale axial photonics (SNAP). Unlike traditional fixed microresonators, this approach allows extensive mechanical adjustment of the device's free spectral range by bending, tilting, or twisting the fibers. The study resolves previous discrepancies between theory and experiment by accounting for extremely small fiber curvatures that critically affect the resonator's properties.
Why it matters
This work establishes a simple, reconfigurable platform for creating high-quality microresonators with widely tunable characteristics, which are essential for applications in optical communications, sensing, and quantum technologies. The mechanical tunability offers significant advantages over conventional monolithic designs that cannot be adjusted after fabrication.
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⚠️ Preprint – Noch nicht peer-reviewed
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Abstract: A widely tunable free spectral range (FSR) is essential for many microresonator applications, but achieving it in compact high-Q systems remains a significant challenge. Surface nanoscale axial photonics (SNAP) provides a route to such devices by localizing whispering-gallery modes through nanoscale effective-radius variations along an optical fiber. Recently, it has been experimentally demonstrated that side-coupling between two optical fibers can induce high-Q SNAP microresonators. In contrast to broadly explored monolithic microresonators, this configuration enables extensive mechanical tuning of the microresonator configuration and FSR through fiber bending, tilting, and twisting. Here, we develop the theory of SNAP microresonators induced at optical fiber intersections, which has remained largely unexplored. We consider weakly twisted fibers, whose geometry can be decomposed into tilting and bending. We show that extremely small fiber curvature critically affects the coupling-induced cutoff frequency variation, the shape of the effective axial potential, and the spectrum of the induced resonator. We discuss the physical origin of this curvature and show that accounting for it resolves the discrepancy between theory and experiment. These findings establish side-coupled optical fibers as a simple, reconfigurable platform for realizing microresonators with a widely tunable FSR.
Source: Widely tunable SNAP microresonators induced at the optical fiber intersections