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A road toward zero-spacing photonic waveguides and circuits


 Like their electronic counterparts, photonic integrated circuits face the challenge of further integration and miniaturization. One of the fundamental limitations comes from the waveguide spacing, which leads to serious crosstalk between the neighboring waveguides when it is less than half a wavelength. Here we demonstrate a potential approach to remove this limitation and realize zero-spacing photonic waveguides with extreme compactness. This is achieved by designing pure-dielectric photonic crystal waveguides with shifted spatial dispersion and arranging them with normal dielectric waveguides alternately. Amazingly, the coupling and crosstalk between the two types of waveguides are negligible despite the zero spacing between them. Through proper designs, zero-spacing photonic bending waveguides and circuits can also be realized in practice. Such a finding opens a new avenue for ultra-compact photonic waveguides and circuits with 100% space utilization efficiency.