Microstructured or “air-clad” fibers, with air holes surrounding a large core, have recently demonstrated much wider light-acceptance angles than conventional fibers. An original and accurate method is presented for determining the numerical aperture of such fibers using leaky modes. The dependence on length, wavelength, and various microstructure dimensions are evaluated for the first time for a class of fibers that exhibit exceptionally high numerical apertures. These results show excellent agreement with published measurements on similar fibers and verify that bridge thicknesses much smaller than the wavelength are required for high numerical apertures.
© 2004 Optical Society of America
Original Manuscript: April 3, 2004
Revised Manuscript: August 7, 2004
Published: November 20, 2004
Nader A. Issa, "High numerical aperture in multimode microstructured optical fibers," Appl. Opt. 43, 6191-6197 (2004)