Spiral fiber gratings for mode coupling

We present some coupling properties of spiral fiber gratings. LP/sub 01/ modes in spiral fiber gratings were demonstrated and analyzed to couple efficiently to both LP/sub 11/ even and odd modes. LP/sub 01/ modes were shown to efficiently couple to both LP/sub 11/ even and odd modes by spiral gratings as predicted. A spiral fiber grating that converts the LP/sub 01/ mode equally to LP/sub 11/ even and odd modes, and a spiral grating that appreciably converts the LP/sub 01/ mode back to the same LP/sub 01/ mode through the LP/sub 01/-to-LP/sub 11/ and LP/sub 11/-to-LP/sub 01/ processes, were also demonstrated and analyzed.