Hoffmann, JahnJahnHoffmannSchulz, Kai MarvinKai MarvinSchulzPitruzzello, GiampaoloGiampaoloPitruzzelloFohrmann, Lena SimoneLena SimoneFohrmannPetrov, Alexander YuAlexander YuPetrovEich, ManfredManfredEich2019-02-072019-02-072018-12-10Scientific Reports 1 (8): - (2018-12-01)https://hdl.handle.net/11420/1991Grating couplers are a fundamental building block of integrated optics as they allow light to be coupled from free-space to on-chip components and vice versa. A challenging task in designing any grating coupler is represented by the need for reducing back reflections at the waveguide-grating interface, which introduce additional losses and undesirable interference fringes. Here, we present a design approach for focusing TM grating couplers that minimizes these unwanted reflections by introducing a modified slot that fulfills an anti-reflection condition. We show that this antireflection condition can be met only for the Bloch mode of the grating that concentrates in the dielectric. As a consequence the light is scattered from the grating coupler with a negative angle, referred to as “backscattering design”. Our analytic model shows that the anti-reflection condition is transferrable to grating couplers on different waveguide platforms and that it applies for both TE and TM polarizations. Our experimentally realized focusing grating coupler for TM-modes on the silicon photonics platform has a coupling loss of (3.95 ± 0.15) dB at a wavelength of 1.55 µm. It has feature sizes above 200 nm and fully etched slots. The reflectivity between the grating coupler and the connected waveguide is suppressed to below 0.16%.en2045-232220181Art.-Nr. 17746Macmillan Publishers Limited, part of Springer Naturehttps://creativecommons.org/licenses/by/4.0/TechnikJournal Articleurn:nbn:de:gbv:830-882.02596110.15480/882.198811420/199110.1038/s41598-018-36082-z10.15480/882.1988Other