High-resolution random fiber laser acoustic emission sensor

A high resolution fiber-optic acoustic emission (AE) sensor using a random fiber laser (RFL) is proposed. The AE probe is undertaken by a random-gratings-based erbium-doped RFL. A narrow linewidth pi-FBG is used as a wavelength locking and sensing element in the RFL. The random distributed feedback in RFL significantly extends the effective cavity length of the laser, thus reduces the thermal frequency noise of the laser and improves the resolution of AE signal. A narrow lasing operation with a 20 dB linewidth of similar to 10.41 kHz and a frequency noise of similar to 10 Hz/p Hz above 1 kHz is realized. The 3x3 coupler interrogation technique is used for signal demodulation. A high AE signal resolution of similar to 280 f epsilon/root Hz @ 1 kHz is obtained. To the best of our knowledge, this is the first time that RFL is used in the 3x3 coupler based AE demodulation scheme to improve the system resolution. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement