Abstract
We present a simple and practical strategy that allows to design high-efficiency grating couplers. The technique is based on the simultaneous apodization of two structural parameters: the grating period and the fill-factor, along with the optimization of the grating coupler etching depth. Considering a 260 nm Si-thick Silicon-on-insulator platform, we numerically demonstrated a coupling efficiency of −0.8 dB (83%), well matching the experimental value of −0.9 dB (81%). Thanks to the optimized design, these results represent the best performance ever reported in the literature for SOI structures without the use of any back-reflector.
Highlights
We present a simple and practical strategy that allows to design high-efficiency grating couplers
Counter-intuitively, the obtained Grating couplers (GC) achieves higher coupling efficiency (CE) than genetic algorithms (GA)-optimized designs reported in the literature that do not use back-reflectors and the reason for this will be clear by the end of the paper
Our results show a non-negligible CE improvement with respect to results reported in[20], where a constant-Λ linear-apodization design was used as the starting configuration for a GA based refinement, highlighting the importance of allowing Λ to vary
Summary
We present a simple and practical strategy that allows to design high-efficiency grating couplers. Considering Silicon-on-Insulator (SOI) technology, the strong refractive index difference between Si and SiO2 allows the implementation of very small, single mode waveguide structures[9] On one hand this enables dense on-chip device integration, but on the other side it makes efficient fiber-to-waveguide coupling challenging because of the vast difference in the mode areas (≈80 μm[2] for fibers and
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