A design of buried square core (BSC) waveguide structure for a polymer based directional coupler at third telecommunication window is presented. The optimization of the waveguide dimension, the waveguide spacing, the coupling length and the thickness of the claddings have been determined. The device length of BSC S-bend waveguide at the input and output ports to form a directional coupler has been studied as a function of radius of curvature and the offset. With the index contrast of 0.0165 between the core and the cladding, the crosstalk of < -26 dB for TE polarization can be achieved.
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