Tunable directional coupler structures based on triangular photonic crystal lattices are investigated using the finite difference time domain method. The infiltration of nematic liquid crystal materials into the coupler waveguides allows for the control of its properties through the application of external static electric fields, which reorient the nematic director. Strong dynamical shifting of the dispersion curves, along with the decoupling frequencies and the coupling coefficient, is demonstrated. Such features render this class of couplers suitable for a range of applications. The coupling lengths accomplished are quite short even when the interaction region between the two coupler branches is widened. Furthermore, operation as a channel interleaver in wavelength division multiplexing systems is explored, and it is revealed that by proper selection of the geometrical parameters a constant channel separation of 0.8nm is achieved, with an overall length of a few hundreds of microns in wide frequency ranges.

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