Highly sensitive fiber random-grating-based random laser sensor for ultrasound detection.

A novel highly sensitive ultrasound sensor based on a random fiber laser is proposed and demonstrated for the first time, to the best of our knowledge. The random fiber laser is constructed with the erbium-doped fiber gain. A fiber random grating provides random-distributed feedback for the random laser and acts as an ultrasound sensing head. The random laser can operate in a single-mode lasing scenario, which offers linear and pure temporal responses to the broadband ultrasonic acoustic emission from 20 kHz to 0.8 MHz. The multiple-interfering reflection spectrum of the random grating provides a large number of steep peak areas over a broad spectral range, which significantly enhances the sensitivity of the random laser sensor and makes it an ideal sensor in harsh environments with large temperature or strain variations. The proposed laser sensor offers signal-to-noise ratio improvement up to 20 dB and higher sensitivity compared with conventional piezoelectric acoustic sensors.