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Focal Ratio Degradation for Fiber Positioner Operation in Astronomical Spectrographs

Belland, Brent and Gunn, James and Reiley, Dan and Cohen, Judith and Kirby, Evan and de Oliveira, Antonio Cesar and de Oliveira, Ligia Souza and Roberts, Mitsuko and Seiffert, Michael (2019) Focal Ratio Degradation for Fiber Positioner Operation in Astronomical Spectrographs. Journal of Astronomical Instrumentation, 8 (3). Art. No. 1950007. ISSN 2251-1717. doi:10.1142/s2251171719500077.

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Focal ratio degradation (FRD), the decrease of light’s focal ratio between the input into an optical fiber and the output, is important to characterize for astronomical spectrographs due to its effects on throughput and the point spread function. However, while FRD is a function of many fiber properties such as stresses, microbending, and surface imperfections, angular misalignments between the incoming light and the face of the fiber also affect the light profile and complicate this measurement. A compact experimental setup and a model separating FRD from angular misalignment was applied to a fiber subjected to varying stresses or angular misalignments to determine the magnitude of these effects. The FRD was then determined for a fiber in a fiber positioner that will be used in the Subaru Prime Focus Spectrograph (PFS). The analysis we carried out for the PFS positioner suggests that effects of angular misalignment dominate and no significant FRD increase due to stress should occur.

Item Type:Article
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URLURL TypeDescription Paper
Cohen, Judith0000-0002-8039-4673
Kirby, Evan0000-0001-6196-5162
de Oliveira, Ligia Souza0000-0001-7670-0204
Additional Information:© 2019 The Author(s). This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 4.0 (CC-BY) License. Further distribution of this work is permitted, provided the original work is properly cited. Received August 8, 2018; Revised December 18, 2018; Accepted January 8, 2019; Published February 21, 2019. We are grateful to the Kavli Institute for the Physics and Mathematics of the Universe, the National Astronomical Observatory of Japan, and the Subaru PFS collaboration for their feedback and recommendations throughout this project. We would especially like to thank Naoyuki Tamura and Yuki Moritani for discussions and direction for this project, as well as Leandro dos Santos for fiber preparation. This material is based upon work supported by the National Science Foundation under MSIP Grant No. 1636426. This research has made use of NASA’s Astrophysics Data System.
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Subject Keywords:Focal ratio degradation; optical fiber; telescope; stress; misalignment
Issue or Number:3
Record Number:CaltechAUTHORS:20200824-122637398
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105073
Deposited By: Tony Diaz
Deposited On:24 Aug 2020 20:14
Last Modified:16 Nov 2021 18:39

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