MEMS Optical Fiber F–P Hydrophone Based on Corrugated PET Diaphragm

In this article, a micro-electro-mechanical system (MEMS) optical fiber Fabry–Perot (F–P) hydrophone based on corrugated polyethylene terephthalate (PET) diaphragms was proposed, fabricated, and measured. Corrugations of different depths were introduced into the PET by simple hot-embossing process. The optical parameters and acoustic characteristics of the fabricated hydrophones were measured and analyzed. In order to maintain a balanced pressure difference between the inside and outside of the F–P cavity, a microflow path structure is designed as a connecting vent and maintains an air cavity, which could improve the sensitivity. Using corrugated PET diaphragms as an acoustic pressure sensitive module of the hydrophones could reduce manufacturing cost, and the measurement results showed that the corrugations could effectively improve the performances of the hydrophones.

I. Introduction

Compared with conventional piezoelectric hydrophone, extrinsic Fabry–Perot interferometric (EFPI) hydrophone has received much attention because of their high sensitivity [1], [2], lightweight [1], anti-electromagnetic interference, and compact size [2], which is widely used in underwater target detection [3], oil and gas exploration [4], biomedical detection [5], underwater monitoring [6], and other fields. The Fabry–Perot (F–P) cavity typically consists of a cleaved lead-in single-mode fiber and a pressure sensitive diaphragm, which will vibrate along with the incident acoustic. People have proposed two types of micro-electro-mechanical system (MEMS) F–P hydrophones. In the first type, a solidified polymer F–P cavity was constructed at the tip of the optical fiber. Several materials, such as polydimethylsiloxane (PDMS), polyethylene terephthalate (PET) [7], and parylene-C, have been adopted. Hydrophones based on these structure show advantages of small size and low cost but suffer the disadvantage of low sensitivity. Therefore, these hydrophones are more likely to be used for ultrasonic sensing. In the second type, an “empty” F–P cavity was constructed between the optical fiber and the surface of the sensing diaphragm. The performance of the hydrophone could be adjusted by modifying the material, size, and reflectivity of the diaphragm.