Multimode waveguide with adiabatic TE0 mode add/drop filter

A device comprising:

• a bus waveguide having a longitudinal axis, wherein the bus waveguide is arranged linearly from a first end of the device to a second end of the device;
• a lower waveguide disposed below the bus waveguide, the lower waveguide translating from a non-overlapping position with respect to the bus waveguide to an overlapping position with respect to the bus waveguide as the lower waveguide extends from the first end of the device to the second end of the device, the lower waveguide tapering in the overlapping position towards the second end of the device;
• and
• an upper waveguide disposed above the bus waveguide and that extends along at least a portion of a path of the lower waveguide,
• wherein opposing longitudinal edges of both the lower waveguide and the upper waveguide, along the at least a portion of the path of the lower waveguide, are located between longitudinal edges of the bus waveguide.

A method comprising:

• receiving a TE1 mode optical signal on a bus waveguide;
• receiving a TE0 mode optical signal on a lower waveguide that is disposed on a layer below the bus waveguide;
• causing the TE0 mode optical signal on a lower waveguide to interact with an upper waveguide disposed on a layer above the bus waveguide to mode multiplex the TE1 mode optical signal and the TE0 mode optical signal without converting the TE0 mode optical signal or the TE1 mode optical signal to another mode;
• and
• outputting the TE0 mode optical signal and the TE1 mode optical signal on the bus waveguide,
• wherein opposing longitudinal edges of both the lower waveguide and the upper waveguide, along at least a portion of respective paths of the lower waveguide and the upper waveguide, are located between longitudinal edges of the bus waveguide.