To obtain high throughput with fibers we have to take into account focal ratio degradation effect, core size, suited coupling configurations, transmission losses.
High throughput with fibers can be obtained with 100 m fibers, corresponding to 3-4 arcsec on the sky. Input microlenses converts the F/16 telescope focal ratio into a better suited F/4-F/5, minimizing focal ratio degradation.
In integral light mode, an adaptor in the telescope focal plane will feed a Polymicro FBP, 100 m core, fiber through a microlens. In polarimetric mode, after passing through a polarimeter, light enters two identical fibers, each one with its own microlens. Light emerging from the 10-15m long fibers is adapted to the collimator focal ratio through a preslit system, a focal elongator F/3.5-F/10. This is based on two achromatic doublets and a field lens delivered by Optosigma.
On the reimaged focal plane a slit mask, placed on a motorized stage, will allow us to select different spectral resolution modes.