Imaging Capabilities of a Long Gradient Index Rod

Abstract

Bundles of small diameter homogeneous optical fibers have been used extensively to transmit spatial information. Because these fibers are non-imaging, the resolution of the bundle is limited by the size of the individual fibers, and the total number of points that can be transmitted is limited by the number of fibers in the bundle. There is also a significant light loss because of the cladding surrounding each fiber. For example, if the core diameter is 10μ and the total diameter 15μ, less than half the incident light can be transmitted. If the index of refraction in a fiber is made to vary continually outward from the optical axis such that the surfaces of constant index are cylinders, the fiber will now be an imaging system. If the fiber is increased in diameter and the parameters chosen correctly, equivalent amounts of spatial information can be transmitted over this single gradient index rod. The total number of resolution points will be limited by the diameter of the rod and the diameter of the image spot.