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Characterization of Mid-Infrared Single Mode Fibers as Modal FiltersWe present a technique for measuring the modal filtering ability of single mode fibers. The ideal modal filter rejects all input field components that have no overlap with the fundamental mode of the filter and does not attenuate the fundamental mode. We define the quality of a nonideal modal filter Q(sub f) as the ratio of transmittance for the fundamental mode to the transmittance for an input field that has no overlap with the fundamental mode. We demonstrate the technique on a 20 cm long mid-infrared fiber that was produced by the U.S. Naval Research Laboratory. The filter quality Q(sub f) for this fiber at 10.5 micron wavelength is 1000 +/- 300. The absorption and scattering losses in the fundamental mode are approximately 8 dB/m. The total transmittance for the fundamental mode, including Fresnel reflections, is 0.428 +/- 0.002. The application of interest is the search for extrasolar Earthlike planets using nulling interferometry. It requires high rejection ratios to suppress the light of a bright star, so that the faint planet becomes visible. The use of modal filters increases the rejection ratio (or, equivalently, relaxes requirements on the wavefront quality) by reducing the sensitivity to small wavefront errors. We show theoretically that, exclusive of coupling losses, the use of a modal filter leads to the improvement of the rejection ratio in a two-beam interferometer by a factor of Q(sub f).
Document ID
20080036096
Acquisition Source
Jet Propulsion Laboratory
Document Type
Preprint (Draft being sent to journal)
Authors
Ksendzov, A.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Lay, O.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Martin, S.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Sanghera, J. S.
(Naval Research Lab. Washington, DC, United States)
Busse, L. E.
(Naval Research Lab. Washington, DC, United States)
Kim, W. H.
(Naval Research Lab. Washington, DC, United States)
Pureza, P. C.
(Naval Research Lab. Washington, DC, United States)
Nguyen, V. Q.
(Naval Research Lab. Washington, DC, United States)
Aggarwal, I. D.
(Naval Research Lab. Washington, DC, United States)
Date Acquired
August 24, 2013
Publication Date
November 9, 2007
Publication Information
Publication: Applied Optics
Publisher: Optical Society of America
Volume: 46
Issue: 32
Subject Category
Optics
Distribution Limits
Public
Copyright
Other
Keywords
single mode fibers
modal filtering
interferometers

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