Enhanced structural sensitivity of hybrid-mode acoustic phonons in axially-varying photonic crystal fiber.

We report the observation of anti-crossings between hybrid-mode acoustic phonons in an axially-varying photonic crystal fiber. Our experimental results are analyzed using an electrostriction theory which reveals strong coupling between longitudinal and shear components of elastic wave. These anti-crossings are highly sensitive to the transverse fiber structure and thus could be potentially used for ultra-sensitive sensors and new opto-acoustic devices.