Subwavelength metamaterial engineering for silicon photonics

Abstract

Waveguides structured at the subwavelength scale frustrate diffraction and behave as optical metamaterials with controllable refractive index. These structures have found widespread applications in silicon photonics, ranging from sub-decibel efficiency fibre-chip couplers to spectrometers and polarization rotators. Here, we briefly describe the design foundations for sub-wavelength waveguide devices, both in terms of analytic effective medium approximations, as well as through rigorous Floch-Bloquet mode simulation. We then focus on two novel structures that exemplify the use of subwavelength waveguides: mid-infrared waveguides and ultra-broadband beamsplitters.

Tilted subwavelength gratings: controlling anisotropy in metamaterial nanophotonic waveguides

“…By approximating the SWG as an isotropic homogeneous material, a wide range of high-performance integrated devices has been demonstrated, including fiber-to-chip grating couplers [10][11][12][13], edge couplers [7,14,15], waveguide couplers [16,17], bragg filters [18,19], and evanescent field waveguide sensors [20,21]. Simple anisotropic models have enabled further applications of SWG waveguides, such as ultra-broadband devices [22,23], polarization management [24,25], or evanescent field confinement [26,27]. However, duty cycle changes affect both polarizations [1], and can also hamper device fabrication due to aspect ratio dependent etching and proximity effects [28].…”