A high performance four-element DFB fiber laser hydrophone array system has been developed and tested. The system has the advantages of low noise floor (<10-6pm/√Hz @ 1 kHz) and wide bandwidth. Acoustic pressure sensitivity of DFB fiber laser hydrophone is 115±3dB re. Hz/Pa. Unbalanced Michelson interferometer and digital phase-generated carrier (PGC) demodulation are adopted to realize high resolution fiber laser wavelength shift demodulation. Four-element DFB fiber laser hydrophone array system performance is tested and its noise equivalent pressure (NEP) is below sea state zero (SS0). The theory analysis, design, development and test of the system are demonstrated in detail.
A compact high-sensitivity distributed feedback (DFB) fiber laser strain sensor with length of only 56 mm is investigated. The intrinsic performances including optical efficiency and acoustic sensing characteristics of bare DFB fiber laser are tested before packaging. Then polyurethane cylinder and spindle structures are applied for fiber laser packaging. By use of a Mach-Zehnder interferometer and a standard optical phase demodulator, the frequency response of DFB fiber laser before and after packaging is tested in a vibration liquid sound field and compared to standard PZT hydrophone. The experimental results show that the prestress on bare fiber laser affects the frequency response rather than strain sensitivity; the frequency sensitivity of spindle structure packaged DFB fiber laser hydrophone is about 113dB•re•Hz•Pa-1 at 1 kHz, which is 55 dB higher than bare fiber laser under the same prestress. It is remarkable that in a quite wide frequency range from 10 Hz to 10 kHz, it has a more flat frequency response with about ±8 dB fluctuation than that of cylinder structure packaged DFB FL.