Fiber modal noise mitigation by a rotating double scrambler

G. Raskin, D. Rogozin, T. Mladenov, C. Schwab, D. Coutts

Research output: Chapter in Book/Report/Conference proceedingConference proceeding contributionpeer-review


Fiber modal noise is a performance limiting factor in high-precision radial velocity measurements with multi-mode fiber fed high-resolution spectrographs. Traditionally, modal noise is mitigated by agitating the fiber, this way redistributing the light that propagates in the fiber over many different modes. However, in case of fibers with only a limited number of modes, e.g. at near-infrared wavelengths or in adaptive-optics assisted systems, this method becomes very inefficient. The strong agitation that would be needed stresses the fiber and can lead to focal ratio degradation. As an alternative approach, we propose to use a classic optical double scrambler and to rotate the scrambler's first fiber end during each exposure. Because of the rotating illumination pattern of the scrambler's second fiber, the modes that are excited vary continuously. This leads to very efficient averaging of the modal pattern at the fiber exit and to a strong reduction of modal noise. In this contribution, we present a prototype design and first laboratory results of the rotating double scrambler.

Original languageEnglish
Title of host publicationAdvances in Optical Astronomical Instrumentation 2019
EditorsSimon Ellis, Céline d'Orgeville
Place of PublicationBellingham, Washington
Number of pages2
ISBN (Electronic)9781510631472
ISBN (Print)9781510631465
Publication statusPublished - 3 Jan 2020
EventAdvances in Optical Astronomical Instrumentation 2019 - Melbourne, Australia
Duration: 9 Dec 201912 Dec 2019

Publication series

NameProceedings of SPIE
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceAdvances in Optical Astronomical Instrumentation 2019


  • Modal noise
  • Optical fiber
  • Radial velocity
  • Spectrograph


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