DIAMETER MEASUREMENT OF SINGLE-MODE FIBER BY USING INTERFEROMETRIC AND IMAGING TECHNIQUES

Two methods to measure the cladding diameter of single-mode fibers are presented. The first method is based on an interference fringe measur ement technique. Interference fringe spacing at two different planes i s measured to determine the cladding diameter of the fiber. The theory of the fringe formation in the interferometeric arrangement using sin gle-mode fibers is discussed. It is theoretically shown that the far-f ield overlapping Gaussian field distribution from the fibers shifts th e position of the fringe maxima and minima. As a special case of unit fringe visibility the minima positions do not shift, whereas the maxim a positions are shifted. In the case of a Lloyd mirror arrangement it is shown that fringes can be obtained from a rough surface as well. A lens is used in the second method to image the two identical point sou rces that cause the interference. Through the use of the magnification and spacing of the images, the cladding diameter is estimated. It is shown that the accuracy of the fiber cladding-diameter measurement can be enhanced by generating multiple point sources. Consistent results of the fiber cladding diameter have been obtained with the proposed me thods. Fiber cladding-diameter measurements with a standard error of l ess than 0. 15 mum can be achieved.