title: High-directionality fiber-chip grating coupler with interleaved trenches and subwavelength index-matching structure.
abstract: We present the first experimental demonstration of a new fiber-chip grating coupler concept that exploits the blazing effect by interleaving the standard full (220 nm) and shallow etch (70 nm) trenches in a 220 nm thick silicon layer. The high directionality is obtained by controlling the separation between the deep and shallow trenches to achieve constructive interference in the upward direction and destructive interference toward the silicon substrate. Utilizing this concept, the grating directionality can be maximized independent of the bottom oxide thickness. The coupler also includes a subwavelength-engineered index-matching region, designed to reduce the reflectivity at the interface between the injection waveguide and the grating. We report a measured fiber-chip coupling efficiency of -1.3  dB, the highest coupling efficiency achieved to date for a surface grating coupler in a 220 nm silicon-on-insulator platform fabricated in a conventional dual-etch process without high-index overlays or bottom mirrors.
authors.forename: Daniel
authors.initials: D
authors.lastname: Benedikovic
authors.forename: Carlos
authors.initials: C
authors.lastname: Alonso-Ramos
authors.forename: Pavel
authors.initials: P
authors.lastname: Cheben
authors.forename: Jens H
authors.initials: JH
authors.lastname: Schmid
authors.forename: Shurui
authors.initials: S
authors.lastname: Wang
authors.forename: Dan-Xia
authors.initials: DX
authors.lastname: Xu
authors.forename: Jean
authors.initials: J
authors.lastname: Lapointe
authors.forename: Siegfried
authors.initials: S
authors.lastname: Janz
authors.forename: Robert
authors.initials: R
authors.lastname: Halir
authors.forename: Alejandro
authors.initials: A
authors.lastname: Ortega-Moñux
authors.forename: J Gonzalo
authors.initials: JG
authors.lastname: Wangüemert-Pérez
authors.forename: Iñigo
authors.initials: I
authors.lastname: Molina-Fernández
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Fédéli
authors.forename: Laurent
authors.initials: L
authors.lastname: Vivien
authors.forename: Milan
authors.initials: M
authors.lastname: Dado