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Publisher DOI: 10.1038/s41598-018-36082-z
Title: Backscattering design for a focusing grating coupler with fully etched slots for transverse magnetic modes
Language: English
Authors: Hoffmann, Jahn 
Schulz, Kai Marvin 
Pitruzzello, Giampaolo 
Fohrmann, Lena Simone 
Petrov, Alexander Yu  
Eich, Manfred 
Issue Date: 10-Dec-2018
Publisher: Macmillan Publishers Limited, part of Springer Nature
Source: Scientific Reports 1 (8): - (2018-12-01)
Abstract (english): 
Grating 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%.
DOI: 10.15480/882.1988
ISSN: 2045-2322
Journal: Scientific reports 
Institute: Optische und Elektronische Materialien E-12 
Document Type: Article
Project: Open Access Publizieren 2018 - 2019 / TU Hamburg 
Mid infrared gas sensing 
License: CC BY 4.0 (Attribution) CC BY 4.0 (Attribution)
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