The present invention relates to a device and a method for optical add/drop multiplexing (OADM) and comprises two MMI structures (3, 23) connected by a MI/MZI waveguide structure (13) comprising wavelength selective means (19, 21, 37, 39), in particular phase shifted Bragg gratings or Bragg gratings of lowpass and highpass type in combination, such that the OADM multiplexer transmits a wavelength channel (nulli) selected in advance and reflects all other channels, wherein a drop functionality is achieved. Simultaneously, a further channel (nullj,) may be added to the multiplexer at the same side as the channel selected in advance is output, where said further channel preferably is centered around the same wavelength as the channel selected in advance. The further channel is transmitted through the Bragg gratings and is superimposed with the other channels, wherein an add functionality is achieved.