A method includes: determining a first material and a second material of a photonic waveguide for propagating light, the photonic waveguide having a first section and a second section arranged in a first layer and a second layer, respectively, of the photonic waveguide; determining a spacing between the first layer and the second layer; determining a parameter set of a crosstalk reduction structure, according to the spacing, the first material and a wavelength of the light, to cause insertion losses of the first section and the second section to be lower than a predetermined threshold; and forming the first and second sections with the first and second materials, respectively, the first section having the crosstalk reduction structure overlapping the second section.