Add-drop multiplexing by grating-induced dispersion in multimode interference device

We present the design for an add-drop multiplexer using a multimode interference device that supports two modes, and incorporates a Bragg grating. This device only exploits the dispersive aspects of the grating in transmission. The grating induces a wavelength-dependent phase difference between the modes inside the structure, effectively inverting the interference pattern at the output of the device over a small wavelength range whereby add-drop functionality is achieved.