Choosing the Right Optical Fiber Coating to Meet Individual Fiber-Optic Strain Measurement Application

Abstract

Accurate optical fiber-based strain measurements in Structural Health Monitoring applications critically depend on proper choice of the fiber coating, which transfers the substrate strains to the fiber core. In this paper, the load-transfer properties of several commercial fiber coatings were experimentally characterized and a transfer gauge length was defined based on an analytical model. The shorter the transfer gauge length, the more accurate is the measurement of complex strain gradients. The coatings evaluated are: standard double-layer acrylate (longest gauge length), ORMOCER® by FBGS, single layer hard acrylate by OFS, and standard polyimide coating (shortest). These gauge length values may help the selection of the proper fiber coating for a specific application, taking into account the actual strain gradients to be measured. Besides, the proposed measurement technique, together with the developed analytical tool, can be used for the characterization of other fiber coatings.