Subwavelength grating (SWG) structures are an essential tool
in silicon photonics, enabling the synthesis of metamaterials
with a controllable refractive index. Here we propose, for the
first time to the best of our knowledge, tilting the grating elements
to gain control over the anisotropy of the metamaterial.
Rigorous finite difference time domain simulations
demonstrate that a 45° tilt results in an effective index variation
on the fundamental TE mode of 0.23 refractive index
units, whereas the change in the TM mode is 20 times smaller.
Our simulation predictions are corroborated by experimental
results. We furthermore propose an accurate theoretical
model for designing tilted SWG structures based on rotated
uniaxial crystals that is functional over a wide wavelength
range and for both the fundamental and higher order modes.
The proposed control over anisotropy opens promising venues
in polarization management devices and transformation
optics in silicon photonics.
