Development and research of fiber-optic hydrophone protective housing

Abstract

Subject of Research.The subject of research is the protective housing for the fiber-optic hydrophone that is a part of the working model of the ocean seismic bottom station. The fiber-optic hydrophone is built on the base of Mach-Zehnder interferometer. Its sensitive arm is wounded on the elastic mandrel. The mandrel material increases acoustic pressure sensitivity of the optical fiber. The developed housing is designed to protect the sensitive optical fiber from mechanical damage. The housing also passes the acoustic signals in water without attenuation in the work frequency range of the fiber-optic hydrophone up to 8 kHz. Method. The theoretical calculations, based on the Helmholtz resonator theory, and mathematical modeling by the finite element method in the ComsolMultiphysics environment were used to develop the protective housing with required parameters. Created models enabled the definition of the protective housing final construction that passes acoustic signals in the required frequency range. Main Results. As a result of mathematical modeling the final construction of the protective housing was chosen. The construction is based on the aluminum cylinder with the external radius equal to 30 mm, the height - 14 cm and the wall thickness - 1 mm and it contains 1900 holes with the radius equal to 1 mm. During the modeling the frequency response of the protective housing was obtained; this response demonstrated its acoustic transparency in water at frequencies up to 8 kHz. The chosen protective housing was fabricated and studied in the working model of the ocean seismic bottom station. Experiment results confirmed the acoustic transparency of the protective housing in the required frequency range. Practical Relevance. The results of this work might be used for the developing and creating of protective housings for fiber-optic hydrophones with the required frequency responses. The developed protective housing is used in the working model of the ocean seismic bottom station and it provides the mechanical protection of the optical fiber in the sensitive element of the fiber optic-hydrophone without distortion of its frequency response.