Graphene Modulators for Silicon Photonic Optical Links

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The backbone of today’s society is the transfer of information. Next-generation data network infrastructures need to support Tb/s data rates. Existing optical fibre communication networks cannot support Tb/s data transmission without consuming an unsustainable amount of power. Optical transceivers send and receive information encoded in light, relying on electro-optic modulators to convert the electrical data signal into the optical domain, and photodetectors to convert the optical signal back into the electrical domain. Power consumption can be reduced by using efficient and compact modulators and photodetectors to integrate the optics closer to the electronics and thus minimise the losses of electrical interconnect at high frequencies. Si photonics technology offers a cost-effective solution for fabricating integrated photonic circuits by combining electronic and photonic components in the same circuit by using existing CMOS technology. This thesis focuses on the development of a scalable graphene-based platform for integrated photonics, and specifically on the electrooptic modulator. I have focused on a double single-layer graphene modulator design in three different configurations that can be used for different types of optical links. This includes a graphene-based electro-absorption modulator, ring resonator modulator, and Mach-Zehnder modulator. The double-layer structure enables the absorption and phase of an optical carrier signal to be electrostatically controlled without the need for doped waveguides. This is the most efficient graphene-based phase modulator to-date with an extracted VπL ∼ 0.12 V·cm, which is ∼ 2 times better than the lowest reported graphene phase modulator. As well as showing very efficient phase modulation, the graphene phase modulator is capable of being operated in the transparency regime where graphene becomes transparent to absorption via interband transitions. Operating in the transparency regime means that the graphene phase modulator is capable of pure phase modulation which is a desirable property for complex modulation formats. Benefiting from efficient phase modulation, the graphene ring resonator modulator has demonstrated an FOM(EA) ∼ 4.48, ∼ 2 times better than the highest currently reported for graphene-based modulators. These results represent a step towards the development of a future graphene-based platform for efficient and compact modulators and photodetectors needed for next-generation optical links.

Ferrari, Andrea C
Graphene, Modulators, Integrated Photonics, Nanotechnology, Opto-electronics, Optical Communication
Doctor of Philosophy (PhD)
Awarding Institution
University of Cambridge
Engineering and Physical Sciences Research Council (1799076)