Distributed feedback fiber laser-based broadband air acoustic sensor using PI film and PEEK shell structure

The optical fiber air acoustic sensor has the advantages of anti-electromagnetic interference, intrinsic safety, and suitable for long-distance transmission. This paper proposes a non-metallic air acoustic sensor which is suitable for high-sensitivity concealed acoustic detection in environments such as electromagnetic interference. The sensor is based on a DFB fiber laser within an air cavity of polyimide (PI) film and poly-ether–ether–ketone (PEEK) shell. The dynamic acoustic response characteristics of the DFB fiber laser modulated by the acoustic-sensitive diaphragm is theoretically studied and numerically simulated. Based on the study and simulation results, a DFB fiber laser acoustic sensor for broadband detection covering the human auditory frequency range is designed and fabricated. An improved phase generated carrier (PGC) demodulation technique is introduced to realize high-resolution dynamic wavelength demodulation and, at the same time, to realize low sensitivity to modulation amplitude and photoelectric changes. The experimental test of the fiber laser air acoustic sensor demonstrated that, in the frequency range of 200 Hz to18 kHz, the sensitivity is − 40.39 dB re.pm/Pa, the fluctuation is less than ± 3.15 dB, and the minimum-detectable pressure (MDP) is 66.7 μPa/√Hz at 1 kHz, and the lower limit of human hearing threshold is reached.