Fundamental Performance Limits of Adaptive Two Wave Mixing Spectral and Phase Demodulator Systems for Fiber Optic Dynamic Strain Sensors

The structural integrity of safety-­‐critical aerospace structures is of enduring concern to the navy. Intelligent Structural Health Management (ISHM) systems can help prevent structural failure of safety-­‐critical structures which cannot be allowed to fail in service. The purpose of an ISHM system is to provide continuous (or on-­‐ demand) information about the state of a structure so that assessment of the structural integrity can be made at any time, and timely remedial actions may be taken as necessary. The method of choice, both from economic and safety points of view, is to instrument the structure with a number of sensors which form the front-­‐ end of the intelligent SHM system by providing information on the condition of the structure. Fiber optic sensors are an increasingly important emerging technology for ISHM systems. Fiber sensor network costs are relatively low, and large distributed sensor networks are possible using multiplexing techniques. The goal of this project is to establish both theoretically and experimentally the fundamental performance limits of adaptive multiplexed two-­‐wave mixing spectral and phase demodulator systems for fiber-­‐optic dynamic strain sensing. Towards this end, we propose to pursue the following tasks that will systematically identify the optimal parameters that can be obtained in each of the subsystems of the demodulators: (i) adaptive source using Fiber Ring Lasers;(ii) TWM demodulation using photorefractive gratings in free-­‐space photorefractive crystals; and (iii) TWM demodulation using population gratings in rare-­‐earth doped fibers.