GeSi Franz-Keldysh modulator for silicon photonic integrated circuits

Abstract

The growing of Internet has driven recent development of Silicon Photonics in the attempt of coping with the unceasing demand of bandwidth at cheap cost; datacentres with large footprint and enormous computational performances are deployed every year with a rate that, by 2021, will represent the 53% of the total count of installed servers. An ambitious yet necessary objective is envisioned by 2030, link speed above 1 Tb/s allowing sophisticated web-services to grow and reach users worldwide. Offering a fast, power efficient and easy to produce, integrated optic modulator working in the C and L band of the communication spectrum for datacentre applications, this thesis presents an innovative Franz-Keldysh based modulator, integrated in a rib waveguide on the 800 nm platform and fully CMOS compatible. The novelties of this design are found in the thick platform, which permits better optical confinement, and the wrap-around junction design that enables definition of wide rib while keeping strong electric field distribution in the active portion of the rib.

Starting from a blank canvas, this project benefited from simulation study, process development and fabrication run. A simulation platform was, in fact, built to estimate electro-optic performances of design variations and define process recipes; the design reference was, then, translated in a set of masks used in the fabrication run. As a result, a device with cutting edge performances was realised, measuring dynamic extinction ratio of 5.2 dB at 56 Gbps with 3dB bandwidth of 56 GHz. Scattering parameters measurements also permitted to evaluate a power consumption of 44 fJ/bit, confirming the exceptional electro-optical efficiency of the design. A side study investigating material engineering by means of rapid thermal annealing to tune the device absorption spectrum, that together with the possibility of customising the device design, permits to expand the operation bandwidth while supporting either the transverse electric or transverse magnetic polarisation, is also presented.

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Identifiers

ORCID for Lorenzo Mastronardi: orcid.org/0000-0003-1489-2778

ORCID for Frederic Gardes: orcid.org/0000-0003-1400-3272

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