Fiber coupling using graded-index rod lenses

The graded-index rod lens (GRIN lens) is useful in coupling between multimode optical fibers. Applications include connectors, switches, multiplexers, and branch couplers. In these devices, one GRIN lens collimates light from an input fiber, and a second lens collects the light and focuses it on an output fiber. This paper presents analyses of power losses in these devices resulting from lateral and angular misalignments and from the spacing between the lenses. It is found that the GRIN lens coupling system is very sensitive to angular alignment but is more tolerant of lateral errors and lens spacing.