Abstract
Subwavelength grating waveguides represent a flexible and perspective alternative to standard silicon-on-insulator
nanophotonic waveguides. In such structures, waves propagate in the form of Bloch modes, in contrast to standard
longitudinally uniform waveguides. Tunability of parameters of subwavelength grating structures possesses a great
advantage of a broad variability of the (effective) refractive index and its dispersion, without significantly increasing
fabrication complexity. A subwavelength grating structure is based on a (quasi)-periodic arrangement of two different
materials, i.e. rectangular nanoblocks of silicon, embedded into a lower-index superstrate, with a period (much) smaller
than the operational wavelength of the optical radiation. Clearly, by changing the filling factor, i.e., the duty-cycle of the
subwavelength grating structure, its effective refractive index can be varied essentially between that of the superstrate
and that of silicon. Our contribution is devoted to a detailed numerical analysis of Bloch modes in subwavelength grating
waveguides and Bragg gratings based on subwavelength grating waveguides. Two independent versions of 3D Fourier
modal methods developed within last years in our laboratories are used as our standard numerical tools. By comparison
with results obtained with a 2D FDTD commercially available method we show that for reliable design of
subwavelength grating waveguide devices of this kind, full-vector 3D methods have to be used. It is especially the case
of Bragg gratings based on subwavelength grating waveguides, as analyzed in this paper. We discuss two options of a
subwavelength grating modulation – designed by changing the subwavelength grating duty cycle, and by misplacement
of Si blocks, and compare their properties from the point of view of fabrication feasibility.
