Yb3+/Er3+-codoped distributed feedback (YbEr-DFB) fibre grating lasers have been investigated for the detection of ultrasonic Lamb waves generated in an aluminum plate. Two sensor configurations have been investigated. A path length imbalanced readout Mach- Zehnder interferometer was used to measure the laser frequency shift induced by ultrasonic vibration. The resolution to out-of-plane displacement was 3 x10-15 m/Ã Â Hz for a continuous ultrasonic wave at a frequency of 470 kHz. Ultrasonic waves were also detected by directly monitoring the laser output power. This simplified configuration is useful for tone burst AE signals generated by a low energy impac
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