This paper describes a single micro-optical fiber sensor capable of measuring three strains simultaneously in a composite structure. This single transducer is based on cascading four micro Fabry-Perot cavities to measure three normal strains and one shear strain in the plane of the optical fiber cross-section. The development of the sensor fabrication and signal processing techniques are discussed. This fabrication includes designing and fabricating new optical fibers, optical fiber circuit, and optical fiber multi-strain sensor head. This paper presents 2D and 3D finite element analysis and 2D closed form analysis to establish the transformation between fiber core and composite host strain stats. FEM is also used to design side-hole fiber for maximized sensitivity to transverse strains. Finally, analytical models are presented for expressing the desired strains in the host composite in terms of the measured optical phase shift in the fiber sensor.
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