Subwavelength gratings (SWG) are periodic structures which behave as controllable homogeneous metamaterials.
SWGs are extremely interesting when they are used in platforms with a limited choice of material refractive
indices, enabling the design of a myriad of high-performance devices. Here we present a novel technique to
gain control over the intrinsic anisotropy of the synthesized metamaterial. We show that tilting the silicon
segments in a SWG structure mainly affects the in-plane (TE) modes, with little impact on the out-of-plane
(TM) modes. Moreover, we present a methodology to quickly but accurately calculate the modes of a tilted
periodic structure modeling the structure as a rotated uniaxial crystal which can be solved with an anisotropic
mode solver. Measurements on a set of fabricated tilted SWG waveguides validate our simulation results. By
using the presented technique, we design a polarization beam splitter based on a 2x2 multimode interferometer.
The design is based on the optimization of the tilting angle to tone the beat length of the TE modes to be a half
of the beat length of the TM modes.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech;
Ministerio de Economía y Competitividad (MINECO) (IJCI-2016-30484, TEC2015-71127-C2-R, TEC2016-80718-R); Ministerio de Educación, Cultura y Deporte (MECD) (FPU16/06762); European Regional Development Fund (ERDF); Comunidad
de Madrid (SINFOTON-CM S2013/MIT-2790); European Association of National Metrology Institutes (EURAMET) (H2020-MSCA-RISE-2015:SENSIBLE, JRP-i22 14IND13 Photind)
