The theoretical investigation of the proposed optical fiber torsion sensor based on computer-generated-hologram (CGH)

Abstract

Optical fiber torsion sensors have significant importance for structural health monitoring. In this paper, an optical fiber torsion sensor based on computer-generated-hologram (CGH) is proposed and investigated theoretically. In the proposed structure a dual mode fiber (DMF) is used as a sensing element. An acoustic source can be employed to induce a fiber grating. The acoustic induced fiber grating (AIFG) causes the fundamental LP01 mode of DMF couples to LP11o and LP11e fiber modes. In the presence of torsion in DMF, the profiles of LP01, LP11o and LP11e modes rotate relative to the absence of fiber torsion. At the end of DMF a suitable CGH can be employed to resolve spatially the contribution of each mode and calculate the fiber twist angle. The proposed optical fiber torsion sensor shows the capability of multi event torsion measurement in the interval [0,π∕2) with the resolution of 0.5 milliradian.