Bending loss of optical fibers: transduction mechanism for fiber-optic sensors

Abstract

We have studied microbending and macrobending effects in fibers to utilize them as transduction mechanisms for fiber-optic sensors. The micro- bending effect is introduced by a periodic microbending along the axis of a multimode fiber, which causes mode coupling. This coupling redistributes the light power among guided (core) modes and couples guided-to-radiated (such as clad) modes. Thus, an applied perturbation, such as acoustic pressure, temperature, and acceleration, which modulates the amplitude of the fiber microbending, can be detected by monitoring the power in certain modes, such as core or clad modes, high- or low- order core modes, or any combination of these modes. The macrobending effect is introduced by a continuous circular fiber bending which causes power radiation from the guided modes. Any modulation of the bending radius caused by an applied field will modulate the power in the guided modes and can thus be detected.