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An optimal method for producing low-stress fibre optic cables for astronomy

Author(s): Murray, Graham; Tamura, Naoyuki; Takato, Naruhisa; Ekpenyong, Paul; Jenkins, Daniel; et al

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Abstract: An increasing number of astronomical spectrographs employ optical fibres to collect and deliver light. For integral-field and high multiplex multi-object survey instruments, fibres offer unique flexibility in instrument design by enabling spectrographs to be located remotely from the telescope focal plane where the fibre inputs are deployed. Photon-starved astronomical observations demand optimum efficiency from the fibre system. In addition to intrinsic absorption loss in optical fibres, another loss mechanism, so-called focal ratio degradation (FRD) must be considered. A fundamental cause of FRD is stress, therefore low stress fibre cables that impart minimum FRD are essential. The FMOS fibre instrument for Subaru Telescope employed a highly effective cable solution developed at Durham University. The method has been applied again for the PFS project, this time in collaboration with a company, PPC Broadband Ltd. The process, planetary stranding, is adapted from the manufacture of large fibre-count, large diameter marine telecommunications cables. Fibre bundles describe helical paths through the cable, incorporating additional fibre per unit length. As a consequence fibre stress from tension and bend-induced ‘race-tracking’ is minimised. In this paper stranding principles are explained, covering the fundamentals of stranded cable design. The authors describe the evolution of the stranding production line and the numerous steps in the manufacture of the PFS prototype cable. The results of optical verification tests are presented for each stage of cable production, confirming that the PFS prototype performs exceptionally well. The paper concludes with an outline of future on-telescope test plans.
Publication Date: 2017
Citation: Murray, Graham, Tamura, Naoyuki, Takato, Naruhisa, Ekpenyong, Paul, Jenkins, Daniel, Leeson, Kim, Trezise, Shaun, Butterley, Timothy, Gunn, James, Ferreira, Decio, Oliveira, Ligia, Sodre, Laerte. (2017). An optimal method for producing low-stress fibre optic cables for astronomy. ASTRONOMICAL OPTICS: DESIGN, MANUFACTURE, AND TEST OF SPACE AND GROUND SYSTEMS, 10401 (10.1117/12.2289829
DOI: doi:10.1117/12.2289829
ISSN: 0277-786X
EISSN: 1996-756X
Type of Material: Conference Article
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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