A New Approach of Large Diameter Polymer-Coated Fiber Laser Hydrophone

Polymer coating of a rather large diameter on distributed feed-back fiber laser generally damages the laser due to differential strain, and hence its usefulness as an effective packaging for hydrophones was not much tested. To overcome this challenge, this paper proposes a special arrangement and demonstrates that it can achieve sensitivity enhancement of 25 dB with improved bandwidth. Using a Mach-Zehnder interferometer, a noise equivalent pressure of 66.5 dB ref. 1 μPa/√Hz at 1 kHz was achieved with flat response up to 4000 Hz. The experimental results are compared with those of an analytical model.