Optical EngineeringDesign of a transverse electric-pass/transverse magnetic-splitting three-guide directional coupler composed of two slot waveguides and one silicon wire
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A three-guide directional coupler composed of two slot waveguides and one silicon wire with a function of transverse electric (TE)-pass/transverse magnetic (TM)-splitting is proposed and designed using a modified 3-D full-vectorial beam propagation method. In our design, quasi-TE modes fed in the middle silicon wire pass through without coupling, whereas quasi-TM modes fed in the same channel are evenly split into the outer slot waveguides. With properly chosen parameters, a TE-pass/TM-splitting directional coupler with a length of 22.6 μm, including the straight coupling region and the S-bends, is achieved with the crosstalk of −31 and −35 dB for quasi-TE and quasi-TM modes, respectively. In addition, the tolerances to the structural parameters and operating wavelength are also investigated in detail.