This paper describes optical propagation beyond the paraxial limit in rotational symmetric short Fabry-Perot cavities and long fibers with parabolic-index profiles. Frequency shifts due to paraxial... Show moreThis paper describes optical propagation beyond the paraxial limit in rotational symmetric short Fabry-Perot cavities and long fibers with parabolic-index profiles. Frequency shifts due to paraxial and nonparaxial effects, the so-called spectral fine structure and vector corrections, are calculated with perturbation theory and expressed in a single dimensionless expansion parameter. The results obtained for short cavities and fibers have similar functional forms but are surprisingly different. These similarities and differences are pointed out and discussed, including their consequences for mode multiplexing in fibers. Show less
