A specklegram in multimode fiber has successfully been used as a sensor for detecting
mechanical disturbance. A cross section of grapefruit fiber is shown in the top part of
the figure. The speckle patterns of the grapefruit fiber (lower left) are much more
complicated and irregular than those of the step-index multimode fiber (lower right). This
method is expected to yield higher sensitivity of mechanical disturbance by using
grapefruit fiber in a single mode - multimode - single mode fiber structure. For details,
see Wang et al., pp. 3543-3548.