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Proceedings Paper

High-efficiency fully etched fiber-chip grating couplers with subwavelength structures for datacom and telecom applications
Author(s): Daniel Benedikovic; Pavel Cheben; Jens H. Schmid; Dan-Xia Xu; Jean Lapointe; Shurui Wang; Siegfried Janz; Robert Halir; Alejandro Ortega-Moñux; Milan Dado
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Paper Abstract

Surface grating couplers are key components to couple light between planar waveguide circuits in silicon-on-insulator (SOI) platform and optical fibers. Here, we demonstrate by using simulations and experiments that a high coupling efficiency can be achieved for an arbitrary buried oxide thickness by judicious adjustment of the grating radiation angle. The coupler strength is engineered by subwavelength structures, which have pitch and feature sizes smaller than the wavelength of light propagating through it, thereby frustrating diffraction effects and behaving as a homogeneous media with an adjustable equivalent refractive index. This makes it possible to apodize the grating coupler with a preferred single etch fabrication process. The coupling efficiency of the grating coupler is optimized for operating with the transverse electric (TE) polarization state at the wavelengths near 1.3 µm and 1.55 µm, which are the bands relevant for datacom and telecom interconnects applications, respectively. The design and analysis of the grating coupler is carried out using two-dimensional (2-D) Fourier-eigenmode expansion method (F-EEM) and finite difference time domain (FDTD) method. The simulations show a peak fiber-chip coupling efficiency of ‒1:61 dB and ‒ 1:97 dB at 1.3 µm and 1.55 µm wavelengths, respectively, with a minimum feature size of 100 nm, compatible with 193 nm deep-ultraviolet (DUV) lithography. The measurements of our fabricated continuously apodized grating coupler demonstrate fiber-chip coupling efficiency of ‒ 2:16 dB at a wavelength near 1.55 µm with a 3 dB bandwidth of 64 nm. These results open promising prospects for low-cost and high-volume fabrication of surface grating couplers in SOI using 193 nm DUV lithography, which is now used in several silicon photonics foundries. It is also predicted that a coupling efficiency as high as ‒ 0:42 dB can be achieved for the coupler structure with a bottom dielectric mirror.

Paper Details

Date Published: 1 May 2015
PDF: 9 pages
Proc. SPIE 9516, Integrated Optics: Physics and Simulations II, 95160I (1 May 2015); doi: 10.1117/12.2177861
Show Author Affiliations
Daniel Benedikovic, Univ. of Žilina (Slovakia)
Pavel Cheben, National Research Council Canada (Canada)
Jens H. Schmid, National Research Council Canada (Canada)
Dan-Xia Xu, National Research Council Canada (Canada)
Jean Lapointe, National Research Council Canada (Canada)
Shurui Wang, National Research Council Canada (Canada)
Siegfried Janz, National Research Council Canada (Canada)
Robert Halir, Univ. de Málaga (Spain)
Alejandro Ortega-Moñux, Univ. de Málaga (Spain)
Milan Dado, Univ. of Žilina (Slovakia)

Published in SPIE Proceedings Vol. 9516:
Integrated Optics: Physics and Simulations II
Pavel Cheben; Jiří Čtyroký; Iñigo Molina-Fernández, Editor(s)

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