TECHNICAL NOTE: An investigation of a fiber optic sensor in the composite cure process

A new sort of fiber optic sensor has been designed. The variation of the refractive index of the resin surrounding the embedded fiber optic was observed by measuring the speckle spatial spectrum at the end-face of the fiber optic. The normalized speckle spatial spectrum is given which depends upon the variation of the refractive index which occurs during the resin cure process. The approximate relation between the refractive index and cutoff frequency is given. The instrumental error of the sensor was estimated by measuring to the refractive index of a matching liquid. The resin cure experimental results are given as measured by the fiber optic sensor. This sort of fiber optic sensor was found to be able to detect the gel point and the end point of the cure process. The fiber optic maintains the wave-guide performance after cure sensing; it was pointed out that this sensor could also be used to sense factors such as temperature and vibration which perturb the structures.