A planar or cylindrical, cantilever-type apparatus including a rigid support. The apparatus further includes a first optical fiber connected to the rigid support, the first optical fiber including a first neutral axis and at least one first wave-guiding core running parallel to the first neutral axis and located at a distance from the first neutral axis, each of the at least one first wave-guiding core including at least one first reflector. The apparatus further includes a first membrane surrounding the first optical fiber; and a first liquid inside the first membrane and surrounding the first optical fiber, the first liquid including a Reynolds number less than one.