Highly selective evanescent modal filter for two-mode optical fibers.

Efficient and selective coupling between a single-mode fiber and the LP(11) mode of a double-mode fiber is demonstrated in an evanescent directional coupler. With greater than 90% coupling to the LP(11) mode, suppression of the coupled power to the lower-order LP(01) mode was measured to be at least 24 dB. This device has application as a modal filter for the construction of in-line all-fiber optical components.