Silver halide single mode fibers for modal filtering in the middle infrared

T. Lewi, A. Ksendzov, S. Martin, O. Lay, S. Shalem, A. Tsun, A. Zayats, A. Katzir, P. Lawson

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

4 Scopus citations


Modal filters are necessary to the proposed high-performance mid-infrared nulling interferometers, because they can help achieve deeper interferometric nulls. Silver halide fibers of composition AgClxBr1-x (0<x<l) are leading candidates for these purposes, due to their high transparency in 4-20 μm spectral range. We have fabricated silver halide fibers with small cores and small differences between the refractive indices of the core and the clad. These operated as single mode fibers. An outer absorbing layer was applied to strip off cladding modes and reduce the minimum fiber length needed for modal filtering. Short sections of such fibers exhibited round and symmetrical optical field mode distributions with losses of 10-15dB/m at λ=10.6μm. We have tested the modal filtering properties of such short fiber sections. We found that the presence of unsuppressed cladding modes at the output is the main factor limiting the fiber's performance as a modal filter. This effect can be mitigated by appropriate aperturing of the output. With a properly sized aperture, a 10.5 cm long fiber can suppress the power in nonfundamental modes by a factor larger than 17000. If an aperture is not used, the suppression is reduced by a factor of ∼20.

Original languageEnglish
Title of host publicationOptical and Infrared Interferometry
StatePublished - 2008
Externally publishedYes
EventOptical and Infrared Interferometry - Marseille, France
Duration: 23 Jun 200827 Jun 2008

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


ConferenceOptical and Infrared Interferometry


  • Middle infrared
  • Modal filtering
  • Nulling interferometry
  • Silver halide
  • Single-mode fiber


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