4most Fiber Feed: Performance And Final Design

The 4MOST(1) instrument is a multi-object-spectrograph for the ESO-VISTA telescope. The 4MOST long fiber feed links the AESOP(2) fiber positioner to two low-resolution spectrographs (1624 fibers) and one high-resolution spectrograph (812 fibers). In addition to the 2436 science fibers, the system includes guide fiber bundles, metrology fiducial fibers and simultaneous calibration fibers for the spectrographs. To validate the design approaches, including fiber connectors and cable rotator, pre-production fiber cables have been built and evaluated. This paper presents the near final design of the fiber feed subsystem and its performance results pertaining to throughput homogeneity, focal ratio degradation, and connector loss of the pre-production cables.