Simultaneous Measurement of two Strain Components Using 3 × 3 and 2 × 2 Coupler-Based Passive Demodulation of Optical Fiber Sensors

This paper uses 3x3 and 2×2 coupler passive demodulation of combined Michelson and polarimetric optical fiber sensors to simultaneously measure axial and transverse strain components in a single optical fiber sensor. The separated Michelson and polarimetric signals are used with isothermal Michelson and polarimetric phase strain models to provide two independent equations describing the strain in the fiber. These equations provide enough information to simultaneously calculate axial and transverse strains in surface mounted sensors. Experiments performed on vibrating cantilever beams show good agreement with measurements made with resistance strain gauges.