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Design of a suspended germanium microantenna for efficient fiber-chip coupling in the long-wavelength mid-infrared range

Design of a suspended germanium microantenna for efficient fiber-chip coupling in the long-wavelength mid-infrared range
Design of a suspended germanium microantenna for efficient fiber-chip coupling in the long-wavelength mid-infrared range

Recent developments of photonic integrated circuits for the mid-infrared band has opened up a new field of attractive applications for group IV photonics. Grating couplers, formed as diffractive structures on the chip surface, are key components for input and output coupling in integrated photonic platforms. While near-infrared optical fibers exhibit large mode field diameters compared to the wavelength, in the long-wave regime commercially available single-mode optical fibers have mode field diameters of the order of the operating wavelength. Consequently, an efficient fiber-chip surface coupler designed for the long-wave infrared range must radiate the power propagating in the waveguide with a higher radiation strength than a conventional grating coupler in the near-infrared range. In this article, we leverage the short electrical length required for long-wave infrared couplers to design a broadband all-dielectric micro-antenna for a suspended germanium platform at 7.67 µm. The design methodology is inspired by fundamental grating coupler equations, which remain valid even when the micro-antenna has only two or three diffractive elements. A simulated coupling efficiency of ~ 40% is achieved with a 1-dB bandwidth broader than 430 nm, which is almost twice the typical fractional bandwidth of a conventional grating coupler. In addition, the proposed design is markedly tolerant to fiber tilt misalignments of ±10°. This all-dielectric micro-antenna design paves the way for efficient fiber-chip coupling in long-wavelength mid-infrared integrated platforms.

1094-4087
22302-22315
Sánchez-Postigo, A.
81499766-b4c1-48ce-8143-9bdd49621d81
Ortega-Moñux, A.
2187ad4e-6b90-4354-83ce-da964b85e0fe
Pereira-Martín, D.
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Molina-Fernández,
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Halir, R.
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Cheben, P.
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Soler Penadés, J.
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Nedeljković, M.
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Mashanovich, G.Z.
c806e262-af80-4836-b96f-319425060051
Wangüemert-Pérez, J. G.
e47666bd-f999-42e2-a234-0745e356c30c
Sánchez-Postigo, A.
81499766-b4c1-48ce-8143-9bdd49621d81
Ortega-Moñux, A.
2187ad4e-6b90-4354-83ce-da964b85e0fe
Pereira-Martín, D.
fae0ad4f-9aad-40eb-8cd6-93a5b4344643
Molina-Fernández,
e7b4acfd-266a-410b-b4b6-1a9c482c77a0
Halir, R.
e3f8d90b-0067-4e1a-a6b1-0217c342dd55
Cheben, P.
9a2e25a5-6aa0-414e-a061-23416efedebc
Soler Penadés, J.
f18f3619-0d71-4547-95fd-dd38c37b7adb
Nedeljković, M.
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Mashanovich, G.Z.
c806e262-af80-4836-b96f-319425060051
Wangüemert-Pérez, J. G.
e47666bd-f999-42e2-a234-0745e356c30c

Sánchez-Postigo, A., Ortega-Moñux, A., Pereira-Martín, D., Molina-Fernández, , Halir, R., Cheben, P., Soler Penadés, J., Nedeljković, M., Mashanovich, G.Z. and Wangüemert-Pérez, J. G. (2019) Design of a suspended germanium microantenna for efficient fiber-chip coupling in the long-wavelength mid-infrared range. Optics Express, 27 (16), 22302-22315. (doi:10.1364/OE.27.022302).

Record type: Article

Abstract

Recent developments of photonic integrated circuits for the mid-infrared band has opened up a new field of attractive applications for group IV photonics. Grating couplers, formed as diffractive structures on the chip surface, are key components for input and output coupling in integrated photonic platforms. While near-infrared optical fibers exhibit large mode field diameters compared to the wavelength, in the long-wave regime commercially available single-mode optical fibers have mode field diameters of the order of the operating wavelength. Consequently, an efficient fiber-chip surface coupler designed for the long-wave infrared range must radiate the power propagating in the waveguide with a higher radiation strength than a conventional grating coupler in the near-infrared range. In this article, we leverage the short electrical length required for long-wave infrared couplers to design a broadband all-dielectric micro-antenna for a suspended germanium platform at 7.67 µm. The design methodology is inspired by fundamental grating coupler equations, which remain valid even when the micro-antenna has only two or three diffractive elements. A simulated coupling efficiency of ~ 40% is achieved with a 1-dB bandwidth broader than 430 nm, which is almost twice the typical fractional bandwidth of a conventional grating coupler. In addition, the proposed design is markedly tolerant to fiber tilt misalignments of ±10°. This all-dielectric micro-antenna design paves the way for efficient fiber-chip coupling in long-wavelength mid-infrared integrated platforms.

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Accepted/In Press date: 28 May 2019
e-pub ahead of print date: 23 July 2019
Published date: 5 August 2019

Identifiers

Local EPrints ID: 433403
URI: https://eprints.soton.ac.uk/id/eprint/433403
ISSN: 1094-4087
PURE UUID: a9e0b7e9-9050-491b-8313-af84aca68fa3
ORCID for J. Soler Penadés: ORCID iD orcid.org/0000-0002-1706-8533

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Date deposited: 20 Aug 2019 16:30
Last modified: 17 Sep 2019 00:32

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Contributors

Author: A. Sánchez-Postigo
Author: A. Ortega-Moñux
Author: D. Pereira-Martín
Author: Molina-Fernández
Author: R. Halir
Author: P. Cheben
Author: M. Nedeljković
Author: J. G. Wangüemert-Pérez

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