Compact acoustic sensor based on air-backed mandrel coiled with optical microfiber.

We propose and demonstrate a compact acoustic sensor comprising a 2 μm diam, 35 mm length optical microfiber coiled around a 3 mm diam air-backed mandrel. Acoustic waves induce local pressure variations that change the mandrel diameter and thus the optical path length of the mode propagating in the microfiber. The phase modulation is detected via a single-fiber polarimetric interferometer. The low stiffness and minimum bend radii of microfibers gives rise to extremely small package sizes without compromising acoustic responsivity.