Abstract
Optical fiber with high numerical aperture (NA) can efficiently relieve the degeneracy of higher-order linearly polarized modes. The degeneracy relief is investigated in two types of high-NA fibers, i.e., low-index-cladding fiber and high-index-core fiber. A naked-core fiber, as with low-index cladding, can be used theoretically to generate the orbital-angular-momentum mode (OAMM) and the cylindrically symmetric modes (CSMs) and . A high-index-core fiber incorporated with high-contrast-index structure can be used similarly to obtain OAMM . The generation of both CSMs and OAMMs required tilted optical gratings to couple the fundamental core mode into these modes. The tilt angle and modulation period of the grating fringes can be calculated simply and visually with the method proposed in this article.
© 2014 Optical Society of America
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