High-Efficiency Random Fiber Laser Based on Strong Random Fiber Grating for MHz Ultrasonic Sensing

An Erbium-gain random fiber laser based on a strong random fiber grating (RFG) is experimentally demonstrated and applied to MHz ultrasound wave detection. The strong RFG with up to −10 dB reflectivity as well as a highly-doped Erbium doped fiber (HD-EDF) enabled a highly efficient random laser radiation with 1-kHz narrow linewidth. With the RFG as the feedback and the sensing head, both burst and continuous ultrasonic signals of up to 8 MHz can be demodulated by dynamics analysis from the random lasing emission. Results show that the detected signal-to-noise ratio (SNR) of 5.1 MHz ultrasound signal remains larger than 43 dB. The proposed random fiber laser sensor provides a broad ultrasonic bandwidth, high sensitivity, simple structure, low cost and robustness to the harsh environment, suggesting prospective applications for ultrasonic wave-associated acoustic emission (AE) detection in structure health monitoring and biomedical diagnosis.