Fig. 4, the distance between the two fiber tips is generally on the order of nanometers and, depending on the gauge length (the active sensing region, defined as the distance between fusion welds). Lcavity is the original cavity length. δ is the change in the cavity length from a given load. The returning light interferes resulting in black and white bands known as fringes (Fig. 4 bottom) caused by destructive and constructive interference. The intensity of these fringes varies due to a change in the optical path length related to a change in cavity length when uni-axial force is applied