Abstract: An optical sensor comprising an optical fiber having a core covered by a cladding, the cladding having an index of refraction different from that of the core, apparatus for retaining the fiber in a sinuously looped disposition, apparatus for fixing the fiber to an object to be sensed whereby movement to be sensed results in one or both of accordion expansion and contraction of loops of the fiber and microbending of the fiber, apparatus for applying a first optical signal into one end of the fiber, apparatus for detecting a resulting optical signal from the other end of the fiber, and apparatus for comparing the first and resulting optical signals to obtain an indication of the movement.