A Static Axial Strain Fiber Ring Cavity Laser Sensor Based on Multi-Modal Interference

A novel and simple static strain fiber ring cavity laser sensor based on all-fiber single-mode-multimode-single-mode (SMS) structure filter is proposed and experimentally demonstrated. When an axial strain is applied on the SMS filter, the pass-band varies, resulting in shifts of the lasing central wavelength. Thus, the value of axial strain imposed on the structure can be calculated by the monitored central wavelength of the system via the function relationship between these two parameters. Compared with the conventional axial strain sensing system based on an SMS fiber structure, the proposal exhibits additional advantages in terms of high optical signal to noise ratio (~ 50 dB) and narrow 3 dB bandwidth apart from simple fabrication and low cost. A good linearity is obtained between the axial strain applied on the SMS filter and central wavelength of the proposed laser sensing system with R² of 0.99954, and high sensitivity of 2.3 pm/με in the range 0-2333 με is successfully achieved.