Abstract: A new annular-core optical fiber is useful, inter alia, for stabilizing the behavior of an optical attenuator based on a Long Period Grating (LPG) against fluctuations in the polarization of the fundamental optical signal. The fiber dimensions and ?n are selected such that when a LPG of some period is used to couple fundamental-mode radiation in the fiber into higher-order modes, the wavelength of peak coupling into an HE mode is removed by at least 30 nm from the wavelength of peak coupling into the nearer of a TE mode or a TM mode.

Abstract: Systems for, and method of, determining propagation characteristics of a photonic structure having a transverse N-fold symmetry. In one embodiment, a system includes: (1) a numerical analyzer that employs a leading order of a systematic homogenization expansion having multiple scales to develop an angularly averaged indexed profile for the photonic structure and (2) a leading order corrector, associated with the numerical analyzer, that further employs the homogenization expansion to refine an imaginary part of an effective index of refraction of the photonic structure.