Harnessing filament arrays for azimuthally resolved displacement sensing in fiber Bragg gratings

A point-by-point femtosecond laser fabrication technique was used to form filament arrays inside single-mode telecommunication fiber. The off-axis positioning of the grating from the neutral axis was key to enabling displacement optical sensing in single mode fiber. Optomechanical responses were enhanced with stress concentration in cantilevered optical fiber. The narrow geometry of the filament array facilitated sensing of a uniform strain field induced by the lateral displacement, or to null the response when filaments were orthogonally oriented. In this way, filament gratings could be overlaid for azimuthally resolved displacement sensing. The ability to measure transverse displacements paves the way toward developing more efficient optical accelerometers.