We propose a three-dimensional waveguide structure for the realization of mode-selective switches. where the high-order spatial modes of a few-mode waveguide can be switched to various single-mode waveguides with thermo-optically controlled vertical asymmetrical directional couplers. To demonstrate the idea. we design and fabricate two specific devices with a polymer material for a wa... https://www.parisnaturalfoodes.shop/product-category/millet/