Manufacturing Long Optical Fiber With Specialty Coatings for Distributed Sensing

Long optical fibers with specialty coatings enable truly distributed fiber optic sensing applications for measuring both physical and chemical parameters in inaccessible or harsh environments. We report an innovative magnetron sputtering deposition process to continuously manufacture up to 1000-m long optical fiber encapsulated with specialty coatings for distributed sensing. Coating materials can be metals, non-metals, metal alloys, oxides, nitrides, or any materials, which can be deposited via magnetron sputtering process. Multiple coatings of different materials can be deposited on optical fiber without interrupting the deposition process. We employed this process to fabricate 60-m-long optical fiber with titanium and palladium coatings for distributed hydrogen sensing. Acting as numerous point hydrogen sensors, the optical fiber was used to detect hydrogen leaks and determine leak locations simultaneously along the entire fiber length. The experimental sensing results demonstrate the capability of the manufacturing process for fabricating long optical fibers with specialty coatings for chemical sensing or other critical applications in extremely high-temperature environments, nuclear radiation environments, or high vacuum environments, where traditional metal coatings or polymer coatings are undesirable.

I. Introduction

Based on principles of Rayleigh scattering, Brillouin scattering or Raman scattering, distributed fiber optic sensing technologies have found a wide range of real-world applications [1]. A distributed fiber optic sensor simply consists of an optical signal interrogation unit and an optical fiber being a sensing element by itself. The signal interrogation units process optical sensing signal travelling along the optical fiber, determine measurands and their locations. By replacing thousands of traditional single-point sensors, a distributed optical fiber sensor can dramatically reduce installation, calibration, and maintenance costs and complexity. It enables sensing solutions with unrivalled advantages especially in inaccessible or inhospitable environments.