Coupler for a graded index fiber

摘要

A concentric core fiber having a low numerical aperture has an end face aligned with the end face of a graded index fiber having a high numerical aperture. The inner core of the concentric core fiber is aligned with and faces the central region of the graded index fiber, while the outer core of the concentric core fiber is aligned with the outer periphery of the inner core of the graded index fiber. In this manner, low order modes which propagate in the inner core of the concentric core fiber are coupled to the central region of the graded index fiber. Higher order modes which propagate in the outer core of the concentric core fiber are applied to the inner core of the graded index fiber and propagate at the edges thereof.