Vertically stacked coupler and serially grafted waveguide: Hybrid waveguide structures formed using an electro-optic polymer

Two hybrid waveguide structures formed using an electro-optic polymer are described. They are a vertically stacked coupler and a serially grafted waveguide. These structures were fabricated by spin-coating, photolithographic, and reactive ion etching processes. Directional coupling was successfully demonstrated between the vertically stacked waveguides, and the crosstalk was −15 dB. This waveguide structure was applied to an optical intensity modulator. The serially grafted waveguide allows butt coupling between the functional waveguide and passive waveguides, and the connection loss at a grafting point was as low as 0.005 dB. This waveguide structure was applied to a Mach–Zehnder optical intensity modulator and a quasi-phase-matched second-harmonic generator.