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 π-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 ∼10.41 kHz and a frequency noise of ∼10 Hz/√Hz above 1 kHz is realized. The 3×3 coupler interrogation technique is used for signal demodulation. A high AE signal resolution of ∼280 fɛ/√Hz @ 1 kHz is obtained. To the best of our knowledge, this is the first time that RFL is used in the 3×3 coupler based AE demodulation scheme to improve the system resolution.