Colorless grating couplers realized by interleaving dispersion engineered subwavelength structures

Abstract

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 3dB 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 1dB bandwidth ∼70 nm, a 3dB bandwidth ∼117 nm, and a peak efficiency ∼-5.1 dB at 1570nm for transverse-electric polarized light. The simulation confirms that the dispersion engineering adds an extra 12nm to the 1dB bandwidth.