Fiber optic polymer cure sensor

An in situ method is presented for monitoring the curing of polymeric compositions, including epoxy- and polymide-based composites. The sensor measures the difference between the refractive index of the cured and uncured composition, with the index increasing as polymerization proceeds. The method differs from all existing methods in that it relies on a self-referential differential measurement rather than on an absolute measurement, the sensor is totally independent of curing conditions and is sensitive to the extent of cure even at the latest stages. It can be used within the body of large composite structures undergoing curing in an autoclave, and it can indicate the end of cure without calibration of any kind