High-Speed Integrated GrapheneSilicon Electro-Optic Modulator

The information age has become a digital explosion, with data growing exponentially at a rate of tenfold every five years. Today's information society is generating an unprecedented amount of data that is stored and processed in data centers and transmitted between data centers and users. In this scenario, data is stored and processed in electrical domain, while information transport takes place in optical domain. Optical communication has been employed to meet the requirement for high-speed data communication. Electro-optic (E/O) modulator converts the information from the electrical domain to the optical domain, thus, is a crucial component for a high-speed optical communication system. A large variety of E/O modulators, including those based on silicon, III-V material, Lithium niobate, Barium titanate, organic electro-optic material and plasmonics have been investigated and demonstrated. Ideally, E/O modulator should encode data at high speed, with large modulation depth, compact footprint, low insertion loss and low driving voltage. However, a modulator that can simultaneously meet all these desirable performance requirements remains elusive. In this thesis, high-speed integrated graphene-silicon E/O modulators have been successfully demonstrated and achieved high overall performance in terms of bandwidth, modulation depth, footprint and driving voltage. This work includes theoretical analysis, numerical simulation, device fabrication and characterization of the graphene-silicon E/O modulators. First, slot waveguide structure is introduced to enhance the light-graphene interaction. Second, a double-layer graphene on silicon slot waveguide-based electron absorption modulator was investigated and demonstrated at both 1.5 μm and 2 μm wavelength bands. The measurement results have shown enhanced modulation efficiency and bandwidth compared with state-of-the-art graphene modulators. Third, double-layer graphene on silicon slot microring modulators were investigated and demonstrated at 1.5 μm and 2 μm wavelength bands, respectively. Graphene microring E/O modulators working at both low Fermi levels and high Fermi levels were characterized. At the low Fermi level region, the graphene modulator shows strong amplitude modulation. While at the high Fermi level region, it shows enhanced phase modulation with negligible amplitude modulation and overcomes the trade-off between the modulation bandwidth and modulation efficiency. As the result, large modulation bandwidth, high modulation depth, compact footprint, acceptable driving voltage and insertion loss were achieved simultaneously.