ABSTRACT
Research and development on the use of optical fibers in sensing principally results from their insensitivity to electromagnetic fields, their light weight and that they are relatively non-intrusive compared to conventional electrical sensors, such as resistive strain gauges [1, 2]. The use of polymers as the base material for optical fiber sensors has traditionally resulted from two key additional advantages. Firstly, their use in simple intensity-based sensor systems [3, 4] is a logical extension of the extensive work undertaken in developing large-core, multi-mode polymer fibers for short-haul transmission systems that are inexpensive, while being easy to handle and terminate. Secondly, any sensor system employing polymer optical fibers (POF) will always have an inherent strain range advantage over equivalent silica-based optical fibers [5]. POF is more flexible than silica, having a far lower Young’s modulus, exhibiting greater fracture toughness which is important when transversely loading the optical fibers, and displays durability in harsh chemical environments. POF also lends itself to modification by a wide spectrum of organic chemical techniques that cannot be used with silica fiber, offering the flexibility to explore new materials or dopants. For example one can add quantum dots or other nano-materials to polymers. Polymer fibers are suitable for in-vivo applications; clinicians already insert polymer catheters into the body, where a silica fiber breakage would be serious. These advantages have been enhanced with the development of specialized polymer optical fibers, which greatly expand the applications of the otherwise limited intensity-based measurements. The new polymer fiber types include step-index solid core fibers, microstructure fibers and fibers that can incorporate grating structures, either Bragg (FBG) or long-period gratings (LPG). The speciality fiber types and grating structures are considered for use in advanced polymer sensor systems.
