Colorless grating couplers realized by interleaving dispersion engineered subwavelength structures

We investigate the waveguide dispersion of subwavelength structures, and propose that the waveguide dispersion can be reduced by reducing the period of subwavelength structures. A 3 dB bandwidth increment of 20% has been observed by introducing this concept into previously demonstrated grating couplers. To fully exploit the bandwidth merits of the structures, gratings with interleaved subwavelength structures were designed and fabricated. Two typical types of interleaving geometries have been investigated. Both demonstrated a 1 dB bandwidth $\sim 70\mathrm{nm}$, a 3 dB bandwidth $\sim 117\mathrm{nm}$, and a peak efficiency $\sim -5.1\mathrm{dB}$ at 1570 nm for transverse-electric polarized light. The simulation confirms that the dispersion engineering adds an extra 12 nm to the 1 dB bandwidth.