The propagation of whispering gallery modes along an optical fiber is fully controlled by nanoscale variation of the effective fiber radius. In the present work we demonstrate the possibility of the creation, tuning, translation and annihilation of arbitrary-shaped transient photonic elements, such as miniature slow light delay lines, dispersion compensators and dispersionless optical buffers, at the surface of an initially regular optical fiber. This is achieved by means of local heating of the fiber with low-power focused CO2 laser radiation, which introduces nanoscale change to the effective radius of the fiber because of thermo-refractive coupling and thermal expansion. The CO2 laser beam is swept along the fiber, with its position and intensity programmably controlled by an acousto-optical deflector, so that the shape and the settling speed for these structures are constrained only by thermal relaxation processes inside the irradiated fiber. Possible realization of a similar technique on a chip, with laser beam heating substituted by on-chip DC heaters, is analysed. The potential application of this method to the on-the-fly fine tuning of the shape of pre-created Surface Nanoscale Axial Photonics (SNAP) elements, particularly providing gates for switching on and off coupling of optical delay elements to a photonic circuit, is also discussed.
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