Transmission and bend loss in far-ultraviolet hollow-core fibers for compact fiber-fed multi-object spectrographs and reflectometers

In this paper we discuss the testing setup, characterization, and applications of hollow core fiber optics designed to transmit light in the far-ultraviolet (FUV; λ < 200 nm). These hollow core fibers were developed at the University of Bath in collaboration with the University of Colorado (CU) Laboratory for Atmospheric and Space Physics (LASP) for potential use in a multiplexed spectrometer for future planetary science instruments. We present an update on the nitrogen-purged test chamber used for throughput and bend loss testing. We find that these fibers exhibit less than 3 dB loss at λ = 170 nm at a bend angle of 90 degrees and a 27 mm radius of curvature. The net transmission of the 20 cm fiber sample in this bend configuration remains greater than 10% for three of the four fiber samples tested, meeting initial requirements for a future prototype fiber-fed instrument. Two of the four fibers tested exceeded 30% transmission. We present these results in detail and provide an update on the development of the Testbed for Fiber-Fed Instrumentation (TUFFI) prototype in development at CU-LASP.