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An optical fiber double scrambler and mechanical agitator system for the Keck planet finder spectrograph

Sirk, Martin M. and Wishnow, Edward H. and Weisfeiler, Marie and Jhoti, Elisha and Curtis, James and Ishikawa, Yuzo and Finstad, Daniel and O'Hanlon, Timothy and Gibson, Steven R. and Edelstein, Jerry and Halverson, Samuel and Roy, Arpita and Howard, Andrew (2018) An optical fiber double scrambler and mechanical agitator system for the Keck planet finder spectrograph. In: Ground-based and Airborne Instrumentation for Astronomy VII. Proceedings of SPIE. No.10702. Society of Photo-optical Instrumentation Engineers (SPIE) , Bellingham, WA, Art. No. 107026F. ISBN 9781510619579. http://resolver.caltech.edu/CaltechAUTHORS:20190103-153504616

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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).


Item Type:Book Section
Related URLs:
URLURL TypeDescription
https://doi.org/10.1117/12.2312945DOIArticle
ORCID:
AuthorORCID
Roy, Arpita0000-0001-8127-5775
Howard, Andrew0000-0001-8638-0320
Additional Information:© 2018 Society of Photo-Optical Instrumentation Engineers (SPIE). The authors thank the Heising-Simons Foundation, the W.M. Keck Foundation, the University of California, Berkeley, the California Institute of Technology, and the University of Hawaii for financial support of KPF. We also thank Claire Poppett and Sharon Jelinsky of the DESI project for help bonding ferrules onto our fibers. This work was performed by SPH under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute.
Funders:
Funding AgencyGrant Number
Heising-Simons FoundationUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
University of California, BerkeleyUNSPECIFIED
University of HawaiiUNSPECIFIED
NASA Sagan FellowshipUNSPECIFIED
Subject Keywords:astronomical instruments: spectrographs, techniques: radial velocity, techniques: spectroscopic, fibers: modal-noise, fibers: scrambling
Record Number:CaltechAUTHORS:20190103-153504616
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20190103-153504616
Official Citation: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, "A optical fiber double scrambler and mechanical agitator system for the Keck planet finder spectrograph," Proc. SPIE 10702, Ground-based and Airborne Instrumentation for Astronomy VII, 107026F (6 July 2018); doi: 10.1117/12.2312945
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92059
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:04 Jan 2019 00:04
Last Modified:04 Jan 2019 00:04

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