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Proceedings Paper

A optical fiber double scrambler and mechanical agitator system for the Keck planet finder spectrograph
Author(s): Martin M. Sirk; Edward H. Wishnow; Marie Weisfeiler; Elisha Jhoti; James Curtis; Yuzo Ishikawa; Daniel Finstad; Timothy O'Hanlon; Steven R. Gibson; Jerry Edelstein; Samuel Halverson; Arpita Roy; Andrew Howard
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Paper Abstract

We present the design and test results of a double-scrambler and fiber agitator system for the Keck Planet Finder (KPF) spectrograph. The mechanical agitator for modal noise suppression is constructed from two linear stages with the fibers mounted in a “W” curve. When driven back-and-forth at different rates, the stages change the position of the fiber curves, and hence vary the modes propagating through the fiber. Near-field temporal centroid shifts caused by modal-noise are reduced by a factor of 100 by the agitator, while mid-range spatial frequencies have reduced power by a factor of ∼300 in the near-field, and ∼1000 in the far-field. The scrambling system incorporates two octagonal fibers, and a scrambler consisting of two identical cemented lenses ∼20 cm apart, which exchanges the optical near- and far-fields of the fibers. The scrambler shows scrambling gains >16,000 in the near-field, and >40,000 in the far-field. The measured throughput efficiency of 99.3% of the expected maximum demonstrates that scrambler-induced focal ratio degradation (FRD) is minimal. The scrambler also serves as the feed-through into the vacuum chamber where the spectrograph is housed, thereby removing concerns about stressing the fibers, and introducing FRD, at this interface. Our illumination stabilization system, consisting of two octagonal fibers, a two lens scrambler, and a mechanical agitator, produces very homogeneous fiber output in both the near and far-fields. When coupled to the Keck Planet Finder spectrograph, this system provides illumination stability corresponding to a velocity of 0.30 m s−1 .

Paper Details

Date Published: 6 July 2018
PDF: 19 pages
Proc. SPIE 10702, Ground-based and Airborne Instrumentation for Astronomy VII, 107026F (6 July 2018); doi: 10.1117/12.2312945
Show Author Affiliations
Martin M. Sirk, Space Sciences Lab., Univ. of California, Berkeley (United States)
Edward H. Wishnow, Space Sciences Lab., Univ. of California, Berkeley (United States)
Marie Weisfeiler, Space Sciences Lab., Univ. of California, Berkeley (United States)
Elisha Jhoti, Univ. of Edingburgh (United Kingdom)
James Curtis, Lawrence Berkeley National Lab., Univ. of California, Berkeley (United States)
Yuzo Ishikawa, Space Sciences Lab., Univ. of California, Berkeley (United States)
San Francisco State Univ. (United States)
Daniel Finstad, Syracuse Univ. (United States)
Timothy O'Hanlon, Space Sciences Lab., Univ. of California, Berkeley (United States)
Steven R. Gibson, Space Sciences Lab., Univ. of California, Berkeley (United States)
Jerry Edelstein, Space Sciences Lab., Univ. of California, Berkeley (United States)
Samuel Halverson, Univ. of Pennsylvania (United States)
Massachusetts Institute of Technology (United States)
Arpita Roy, California Institute of Technology (United States)
Andrew Howard, California Institute of Technology (United States)


Published in SPIE Proceedings Vol. 10702:
Ground-based and Airborne Instrumentation for Astronomy VII
Christopher J. Evans; Luc Simard; Hideki Takami, Editor(s)

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