A test bed for simultaneous measurement of ber near and far-eld for the evaluation of ber scrambling properties

To improve our understanding of ber scrambling properties a test bed where ber near-eld and far-eld can be measured simultaneously is described. A variety of measurements has been conducted with a selection of bers from dierent vendors, including state-of-the-art octagonal and hexagonal bers. After characterization of the test bench with respect to stability and resolution, scrambling measurements have been conducted using LEDs with central wavelengths ranging between 465-635 nm. The dependence on wavelength regarding to photometrical scrambling has been initially demonstrated. Moreover, two mechanical combined ber cables have been analyzed that were made from octagonal-circular and hexagonal-octagonal ber sections. In this context an apparatus for focal ratio degradation (FRD) measurements was assembled to compare dierent shaped bers and ber combinations. Finally, all these preliminary investigations will help in choosing a ber with good radial scrambling performance for the next generation ber-link of the ber optic coupled Cassegrain echelle spectrograph FOCES intended to be operated at the 2.0 m Fraunhofer Telescope at the Wendelstein Observatory.