Fiber optic strain sensor with femto-strain resolution based on differentiating interferometer

A high resolution white-light driven strain sensor is proposed based on a differentiating interferometer. The differentiating Mach-Zehnder interferometer with a delay fiber is used as the sensing element. The strain is obtained by demodulating the phase signal using three-channel Kalman filter tracking. The strain frequency response of the differentiating interferometer is analyzed and tested. Increasing the length of the delay fiber can improve the strain sensitivity while sacrificing the measurement frequency band, thereby improving the strain resolution. Experimental results show that the proposed sensor achieves a strain resolution limit of 9 fϵ/√Hz and can sense strains smaller than the nano-strain level. This confirms its potential to be used in applications requiring nano-strain or femto-strain measurements.