Patent ID: 8363987

Claim:
A mode-selective add/drop unit (MSADU) for a mode division de/multiplexing (MDM) device comprising: an optical ADU waveguide adapted for coupling to an input optical waveguide, said optical ADU waveguide having: at least one region providing optical signal coupling between the ADU waveguide and a multi-mode waveguide; one or more phase matching regions for controlling a phase difference between an electromagnetic wave (EMW) carried in the ADU waveguide and the multi-mode waveguide; a transition region connecting the optical signal coupling and a phase matching region; and, a width changer region having a continuous width-changing profile for transferring optical signal at a fundamental mode in said input optical waveguide to a fundamental mode of said ADU waveguide, wherein said profile of said width changer region ensures width continuity and continuity of first and second derivatives at a coupling boundary between said input optical waveguide and the ADU waveguide.