Fiber ring laser for axial micro-strain measurement by employing few-mode concentric ring core fiber

•The characteristics of a novel few-mode concentric-ring core fiber are showed.•We demonstrated LP01 and LP11 are two dominated propagating modes in CRCF.•An axial micro-strain sensor based on fiber ring laser is proposed.•The sensing system has high OSNR (∼45 dB) and narrow 3 dB bandwidth (∼0.1 nm).•The sensor has an experimentally axial micro-strain sensitivity of ∼0.81pm/με.

We proposed and demonstrated a novel few-mode concentric-ring core fiber (FM-CRCF) for axial micro-strain measurement with fiber ring laser based on few-mode-singlemode-few-mode fiber structure. The core area of CRCF consists of four concentric rings which refractive indices are 1.448, 1.441, 1.450, 1.441, respectively. LP01 and LP11 are two dominated propagating mode groups contributing in the CRCF. In this few-mode-singlemode-few-mode structure, two sections of CRCF act as the mode generator and coupler, respectively. The basis of sensing is the center single mode fiber. Moreover, this structure can be used as an optical band-pass filter. By using fiber ring cavity laser, the axial micro-strain sensing system has high intensity (∼20 dB), high optical signal to noise ratio (∼45 dB) and narrow 3 dB bandwidth (∼0.1 nm). In the axial micro-strain range from 0 to 1467με, the lasing peak wavelength shifts from 1561.05 nm to 1559.9 nm with the experimentally sensitivity of ∼0.81pm/με.