A field-profile transformer utilizing a graded-index oval-core (GIO) fiber

A field-profile transformer utilizing a graded-index (GI) fiber having an oval core is proposed. Numerical investigation has demonstrated that the new fiber is capable of performing the profile transformation from elliptical fields that have high aspect ratios of up to 9, to circular fields, and vice versa. Experimental verification is also performed at a wavelength of 1550 nm, by making use of plastic GI fibers, demonstrating that a circular modal field of a standard single-mode fiber can be transformed into an elliptical field with an aspect ratio of 4.1. The transformer shows promise for low-loss coupling between fibers and functional devices that have elliptical fields, such as planar waveguides, semiconductor optical amplifiers, and laser diodes.