Abstract
In this communication, we report about the design, fabrication, and testing of Silicon-based photonic integrated circuits
(Si-PICs) including low-loss flat-band slow-light high-contrast-gratings (HCGs) waveguides at 1.31 μm. The light slowdown
is achieved in 300-nm-thick silicon-on-insulator (SOI) rib waveguides by patterning adiabatically-tapered highcontrast
gratings, capable of providing slow-light propagation with extremely low optical losses, back-scattering, and
Fabry-Pérot noise. In detail, the one-dimensional (1-D) grating architecture is capable to provide band-edge group
indices ng ~ 25, characterized by overall propagation losses equivalent to those of the index-like propagation regime (~
1-2 dB/cm). Such photonic band-edge slow-light regime at low propagation losses is made possible by the adiabatic
apodization of such 1-D HCGs, thus resulting in a win-win approach where light slow-down regime is reached without
additional optical losses penalty. As well as that, a tailored apodization optimized via genetic algorithms allows the
flattening of slow-light regime over the wavelength window of interest, therefore suiting well needs for group index
stability for modulation purposes and non-linear effects generation. In conclusion, such architectures provide key
features suitable for power-efficient high-speed modulators in silicon as well as an extremely low-loss building block for
non-linear optics (NLO) which is now available in the Si photonics toolbox.
