Journal
OPTICS EXPRESS
Volume 18, Issue 12, Pages 12736-12747Publisher
OPTICAL SOC AMER
DOI: 10.1364/OE.18.012736
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Funding
- NASA [NNX09AC92G]
- NSF [AST-0905214, 0905592]
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [0905592, 0905214, 0804441] Funding Source: National Science Foundation
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [0804311] Funding Source: National Science Foundation
- NASA [NNX09AC92G, 120467] Funding Source: Federal RePORTER
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We propose and analyze a new approach to generate a broadband astro-comb by spectral broadening of a narrowband astro-comb inside a highly nonlinear optical fiber. Numerical modeling shows that cascaded four-wave-mixing dramatically degrades the input comb's side-mode suppression and causes side-mode amplitude asymmetry. These two detrimental effects can systematically shift the center-of-gravity of astro-comb spectral lines as measured by an astrophysical spectrograph with resolution approximate to 100,000; and thus lead to wavelength calibration inaccuracy and instability. Our simulations indicate that this performance penalty, as a result of nonlinear spectral broadening, can be compensated by using a filtering cavity configured for double-pass. As an explicit example, we present a design based on an Yb-fiber source comb (with 1 GHz repetition rate) that is filtered by double-passing through a low finesse cavity (finesse = 208), and subsequent spectrally broadened in a 2-cm, SF6-glass photonic crystal fiber. Spanning more than 300 nm with 16 GHz line spacing, the resulting astro-comb is predicted to provide 1 cm/s (similar to 10 kHz) radial velocity calibration accuracy for an astrophysical spectrograph. Such extreme performance will be necessary for the search for and characterization of Earth-like extra-solar planets, and in direct measurements of the change of the rate of cosmological expansion. (C) 2010 Optical Society of America
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