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We investigate the evanescent coupling of femtosecond laser written waveguides with elliptical and circular shape. A directional tuning the coupling properties is realized in a cubic array by tilting the elliptical waveguides. This allows to specifically pronounce diagonal coupling. In contrast, directional insensitive coupling is demonstrated in a circular waveguide array based on circular waveguides.
Szameit et al. (Mon,) studied this question.