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Grating-frustrated coupler: a novel channel-dropping filter in single-mode optical fiber.

A low-insertion-loss, all-single-mode fiber, wavelength-division-multiplexing filter comprising a four-port polished coupler and a strong fiber grating is demonstrated. The device operated in a novel way by a process we call grating-frustrated directional coupling. A fiber grating, present in only one half of the coupler, frustrates the transference of power to the other half within a narrow wavelength range. The performance of a prototype device - a 1535-nm channel-dropping filter with 0.7-nm bandwidth, 70% peak transmission, and 13-dB isolation-shows great promise for wavelength-division-multiplexing and line-filtering applications.