The image quality of an uncoated fiber bundle is influenced by light leakage between neighboring fibers. The point-spread function due to light leakage between neighboring fibers is used to calculate the static and dynamic frequency response of an uninsulated fiber bundle. The static and dynamic frequency response is also measured for a bundle of uncoated fibers. The possibility of optically insulating smaller diameter fibers by depositing a thin coating of low refractive-index plastic material is well known. A process for drawing glass fibers with a core of high refractive-index glass and a 1–2-µ thick coating of low refractive-index glass has been developed. This method is also used for depositing a second metal coating on fibers and drawing “multiple fibers.” A discussion on the dependence of the coating thickness on various parameters of the over-all optical system is given.
N. S. KAPANY, "Fiber Optics. VI. Image Quality and Optical Insulation," J. Opt. Soc. Am. 49, 779-784 (1959)