Long-period-grating-assisted optical add-drop filter based on mismatched twin-core photosensitive-cladding fiber.

A noninterferometric optical fiber add-drop channel filter based on a mismatched twin-core photosensitive-cladding fiber and long-period fiber grating is demonstrated. With assistance from the fiber grating, co-directional spectrally selective cross coupling between the two cores can be realized with an efficiency of 90%.