Embedded-Optical-Fiber, Near-Infrared Fluorosensor for NDE of Aerospace Systems

Conventional fiber optic fluorosensors absorb and re-emit in the UV/VIS spectral range. The unavailability of UV/VIS light sources makes these fluorosensors prohibitively costly and unreliable. Systems & Processes Engineering Corporation (SPEC) proposes to develop an embedded fiber optic near-infrared (NIR) fluorosensor which uses reliable and inexpensive diode lasers as light sources. The embedded fiber optic fluorosensor will combine (1) Phase Resolved Fluorescence Spectroscopy (PRFS) to exploit fluorescence lifetime which is more sensitive to fluorescence changes induced by cladding immobilized, NIR fluorescent molecules complexed with metal ions produced by airframe corrosion, and (2) SPEC's digital optical phase-locked-loop (DOPLL) for strain, stress and vibration measurements. The system when integrated into the airframe will provide real time monitoring of the health of bonding joints and critical failure locations (e.g. fasteners, bolts, composite joints, welds) on an aircraft by monitoring corrosion by-products (metal ions). The envisioned system will feature the following technologies: NIR absorbing probe molecules; optical cladding immobilized with fluorescent dye molecules; fluorescence lifetime measured by PRFS; strain, stress, and vibration measurement by DOPLL; and optoelectronic miniaturization technology. The resulting system will be lOO times smaller and faster, and 1/4 the cost of existing commercial fluorosensors.