A modal-field transformer for LD modules

An effective modal field transformer is proposed and its experimental performance is reported. The graded-index oval-core (GIO) fiber is fabricated by making use of a plastic fiber. A circular field has been converted into an elliptic one that has an aspect ratio of 3.2. The GIO fiber promises efficient coupling from laser diodes that have highly elliptical fields to single-mode fibers as a new type of lensed fiber.