title: Controlling leakage losses in subwavelength grating silicon metamaterial waveguides.
abstract: Subwavelength gratings (SWG) are photonic structures with a period small enough to suppress diffraction, thereby acting as artificial dielectric materials, also called all-dielectric metamaterials. This property has been exploited in many high-performance photonic integrated devices in the silicon-on-insulator (SOI) platform. While SWG waveguides are theoretically lossless, they may exhibit leakage penalty to the substrate due to a combination of reduced modal confinement and finite thickness of the buried oxide (BOX) layer. In this Letter, for the first time, to the best of our knowledge, we analyze substrate leakage losses in SWG waveguides. We establish a direct relation between the effective index of the waveguide mode and the leakage losses which, remarkably, is independent of the geometric parameters of the SWG waveguide. This universal relation is demonstrated both numerically and experimentally, and it provides practical design guidelines to mitigate leakage losses. For BOX thicknesses of 2 and 3 μm, we find negligible leakage losses when the mode effective index is higher than 1.65 and 1.55, respectively.
authors.forename: J Darío
authors.initials: JD
authors.lastname: Sarmiento-Merenguel
authors.forename: Alejandro
authors.initials: A
authors.lastname: Ortega-Moñux
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Fédéli
authors.forename: J Gonzalo
authors.initials: JG
authors.lastname: Wangüemert-Pérez
authors.forename: Carlos
authors.initials: C
authors.lastname: Alonso-Ramos
authors.forename: Elena
authors.initials: E
authors.lastname: Durán-Valdeiglesias
authors.forename: Pavel
authors.initials: P
authors.lastname: Cheben
authors.forename: Íñigo
authors.initials: Í
authors.lastname: Molina-Fernández
authors.forename: Robert
authors.initials: R
authors.lastname: Halir