The fiber system is designed to transmit the light from 5,000 science targets imaged at the telescope’s prime focus to DESI’s spectrographs.

Each optical fiber, with a 107-micron-diameter core, is terminated in a ferrule that is then mounted in a robotic fiber positioner. The fibers are collected behind the focal plane into 10 groups of 500. Each group spans 47.5 meters from the focal plane to the spectrograph room via guides, supports, strain-relieving spool boxes, and ruggedized cables. Each group of 500 fibers is then precisely arranged and terminated into a linear arc that provides the optical entrance-slit illumination to an associated spectrograph.