Adiabatic mode conversion in multimode waveguides using chirped computer-generated planar holograms

We discuss the design of a mode converter based on optical analogy of adiabatic passage via a level crossing in multimode waveguides. Computer-generated planar holograms are used to implement the chirped gratings that mimic the laser excitation used in the transfer between quantum states of atoms and molecules. The mode coupling properties are analyzed using the coupled mode theory and shown to resemble the level crossing process. Key features of the devices are illustrated with theoretical calculations and numerical examples. The proposed mode converter shows a bandwidth in excess of 300 nm in the optical communications band.