An Improved Polymer Shell Encapsulated Fiber Laser Hydrophone

Fiber laser hydrophones engineered either with a direct polymer coating over the laser or a coating over a mechanically enclosed laser have many practical limitations. Notably, damages can occur due to the differential strain and the complexity involved in the fabrication of the mechanical enclosure and micropositioning it over the laser. This paper proposes a simpler fiber laser hydrophone encapsulated in a polymer shell with enhanced sensitivity and broad bandwidth. The significant factors that influence the hydrophone and its acoustic performance are studied in detail using a 2-D-axisymmetric finite-element analysis (FEA) and analytical methods. The obtained experimental results are found to corroborate those of the analytical and FEA methods. The method of fabricating the hydrophones and the measurements are found to be repeatable. A sensitivity of -155 dB ref. 1 V/μPa with a bandwidth of 6 kHz was obtained from our experiments and can further be tuned to the requirements.