A Rugged Optical Fiber Interferometer for Strain Measurements Inside a Composite Material Laminate

A simple Mach-Zehnder Interferometer has been constructed entirely of single-mode optical fibers. The signal arm was successfully embedded inside a graphite-epoxy laminate. Tensile and compressive strains internal to the laminate were measured for the deformation of a cantilevered beam to demonstrate the system functionality. Difficulties encountered during the measurement of the compressive strains are discussed. The resulting optical system eliminates entirely the need for conventional optical components, while maintaining the conditions required to obtain optical interference necessary for strain measurement.