Measurement of fiber diameters and detection of defects.

摘要

Methods for measuring the diameters of transparent filaments with high precision are provided. The methods involve determining the average spatial frequency of the far-field interference pattern produced by illuminating the filament with a beam of laser light using discrete sequence Fourier transforms (DSFTs). Methods are also provided for making the diameter measurement insensitive to filament ellipticity by determining the diameter at two locations which are spaced apart by an amount such that a plot of diameter versus angle of rotation for an elliptical filament calculated at the first location is approximately 90 DEG out of phase from the same plot calculated at the second location. Methods for detecting defects in filaments are also provided in which a characteristic peak in the spatial frequency spectrum of the interference pattern which subdivides into two peaks which migrate in opposite directions as the defect grows in size is detected. <IMAGE>