Expanding the core: a new approach for the design of single-mode waveguides

A new approach is proposed for the design of single-mode waveguides. The approach is based on slicing the core of the waveguide into a uniform array of subwaveguides and expanding the separation between these waveguides up to the point where the array is still supporting a single supermode. By appropriate selection of the array design parameters, it is possible to get more than fourfold expansion in the modal width of the single-core waveguide (SCW). This expansion allows for the design of single-mode waveguides with weakly guidedlike modal widths under high index-contrast conditions. The expanded-core waveguides (ECWs) combine these larger modal widths with stronger modal confinement factors compared to the SCWs. Numerical computations of specific design examples are included to compare between ECWs and SCWs for both passive- and active-waveguide applications.