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Germanium-on-silicon mid-infrared grating couplers with low-reflectivity inverse taper excitation

Germanium-on-silicon mid-infrared grating couplers with low-reflectivity inverse taper excitation
Germanium-on-silicon mid-infrared grating couplers with low-reflectivity inverse taper excitation
A broad transparency range of its constituent materials and compatibility with standard fabrication processes make germanium-on-silicon (Ge-on-Si) an excellent platform for the realization of mid-infrared photonic circuits. However, the comparatively large Ge waveguide thickness and its moderate refractive index contrast with the Si substrate hinder the implementation of efficient fiber-chip grating couplers. We report for the first time, to the best of our knowledge, a single-etch Ge-on-Si grating coupler with an inversely tapered access stage, operating at a 3.8 µm wavelength. Optimized grating excitation yields a coupling efficiency of -11 dB (7.9%), the highest value reported for a mid-infrared Ge-on-Si grating coupler, with reflectivity below -15 dB (3.2%). The large periodicity of our higher-order grating design substantially relaxes the fabrication constraints. We also demonstrate that a focusing geometry allows a 10-fold reduction in inverse taper length, from 500 to 50 µm.
Diffraction gratings, Infrared, Integrated optics devices
0146-9592
4324-4327
Alonso-Ramos, Carlos
93f2937e-a94b-4b66-b6fc-276efa88272f
Nedeljković, Milos
b64e21c2-1b95-479d-a35c-3456dff8c796
Benediković, Daniel
5fdecaa0-eb77-4bd4-b2b7-18de41ea52be
Soler Penadés, Jordi
f18f3619-0d71-4547-95fd-dd38c37b7adb
Littlejohns, Callum
0fd6585d-030d-4d8f-a411-6fc03e083efa
Khokhar, Ali
2eedd1cc-8ac5-4f8e-be25-930bd3eae396
Perez-Galacho, Diego
59043094-c701-43fe-840e-641798157165
Vivien, Laurent
59537381-cb28-458b-9bca-2f76ce99b57a
Cheben, Pavel
ab8ffd13-bc5c-44cb-88ed-605e3c347848
Mashanovich, Goran
c806e262-af80-4836-b96f-319425060051
Alonso-Ramos, Carlos
93f2937e-a94b-4b66-b6fc-276efa88272f
Nedeljković, Milos
b64e21c2-1b95-479d-a35c-3456dff8c796
Benediković, Daniel
5fdecaa0-eb77-4bd4-b2b7-18de41ea52be
Soler Penadés, Jordi
f18f3619-0d71-4547-95fd-dd38c37b7adb
Littlejohns, Callum
0fd6585d-030d-4d8f-a411-6fc03e083efa
Khokhar, Ali
2eedd1cc-8ac5-4f8e-be25-930bd3eae396
Perez-Galacho, Diego
59043094-c701-43fe-840e-641798157165
Vivien, Laurent
59537381-cb28-458b-9bca-2f76ce99b57a
Cheben, Pavel
ab8ffd13-bc5c-44cb-88ed-605e3c347848
Mashanovich, Goran
c806e262-af80-4836-b96f-319425060051

Alonso-Ramos, Carlos, Nedeljković, Milos, Benediković, Daniel, Soler Penadés, Jordi, Littlejohns, Callum, Khokhar, Ali, Perez-Galacho, Diego, Vivien, Laurent, Cheben, Pavel and Mashanovich, Goran (2016) Germanium-on-silicon mid-infrared grating couplers with low-reflectivity inverse taper excitation. Optics Letters, 41 (18), 4324-4327. (doi:10.1364/OL.41.004324).

Record type: Article

Abstract

A broad transparency range of its constituent materials and compatibility with standard fabrication processes make germanium-on-silicon (Ge-on-Si) an excellent platform for the realization of mid-infrared photonic circuits. However, the comparatively large Ge waveguide thickness and its moderate refractive index contrast with the Si substrate hinder the implementation of efficient fiber-chip grating couplers. We report for the first time, to the best of our knowledge, a single-etch Ge-on-Si grating coupler with an inversely tapered access stage, operating at a 3.8 µm wavelength. Optimized grating excitation yields a coupling efficiency of -11 dB (7.9%), the highest value reported for a mid-infrared Ge-on-Si grating coupler, with reflectivity below -15 dB (3.2%). The large periodicity of our higher-order grating design substantially relaxes the fabrication constraints. We also demonstrate that a focusing geometry allows a 10-fold reduction in inverse taper length, from 500 to 50 µm.

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GOS_Grating RevManuscript.pdf - Accepted Manuscript
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More information

Accepted/In Press date: 12 August 2016
e-pub ahead of print date: 22 August 2016
Published date: 13 September 2016
Additional Information: Funded by Royal Society: Royal Society Fellowship (UF100047)
Keywords: Diffraction gratings, Infrared, Integrated optics devices
Organisations: Optoelectronics Research Centre

Identifiers

Local EPrints ID: 404442
URI: https://eprints.soton.ac.uk/id/eprint/404442
ISSN: 0146-9592
PURE UUID: 23a4b888-9e4a-4351-8d21-03ce81c7859c
ORCID for Milos Nedeljković: ORCID iD orcid.org/0000-0002-9170-7911
ORCID for Jordi Soler Penadés: ORCID iD orcid.org/0000-0002-1706-8533

Catalogue record

Date deposited: 10 Jan 2017 12:32
Last modified: 10 Dec 2019 06:16

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