Optical Modulation And Control In Silicon Photonic Structure With Plasmonic Effect

Silicon photonic circuit is considered to be a promising solution thatcan provide future on-chip interconnects with large communicationbandwidths and low power consumptions which are required by Moore’slaw. In the past few years, remarkable progresses in silicon photonics havebeen made, which yields unprecedented control over the optical propertiesand the fabrication processes. Ultra-dense photonic integrated circuits canbe seamlessly integrated to the CMOS chip manufacturing process. Alot ofuseful silicon photonic components, including light sources, switches,electro-optic modulators and detectors have been fabricated. While thesesilicon-based electro-optic devices have been reported, they require largedevice footprints on the order of millimeter as a result of relatively lowmode confinement and weak non-linear electro-optical coefficient. Theoptical mode confinement can be increased by employing a high-Qresonator structure, however this will signifcantly sacrifce bandwidth.Furthermore, electrode-layout design challenges and thermal effects limitthe deployment of silicon photonics. These constrains can besimultaneously overcome by two aspects: firstly, to enhance the opticalmode overlap with the actively index-modulated region, e.g., the regionwith electro-optic effect; secondly, to enhance the light-matter-interactionof the optical mode with the actively index-modulated material viaincreasing the electromagnetic-feld strength. A silicon-plasmonic hybridplatform may provide us a solution to achieve both the above desiredfeatures. This platform combines the advantages including high modeconfinement of plasmonic structure and CMOS compatibility of traditionalphotonic structure, which could be an effective method for the future development of silicon photonics. The major research achievements andcontributions of this dissertation are summarized as follows:1) We propose a silicon-compatible plasmonic electro-optic modulatoremploying a silicon racetrack ring resonator coupled to a buswaveguide. A silicon-plasmonic hybrid phase shifter clad withelectro-optic polymer is introduced to achieve high-speed performanceand low energy consumption. Three dimensional finite-differencetime-domain method and optical transmission matrix are used toanalyze the hybrid phase shifter. Simulations show that the proposedmodulator can achieve a high extinction ratio of more than15dB at1550-nm wavelength under a1.2-V bias voltage. The operationprinciple of the hybrid phase shifter and the phase-velocity matchconditions have been demonstrated in dimensional parameterconfiguration process. The misalignment tolerance and fabricationfeasibility of the modulator are also discussed. The silicon-plasmonichybrid structure may provide us a solution to achieve more compactsilicon photonics.2) We have proposed a conductor-gap-dielectric (CGD) waveguide actingas an electro-optic phase shifter. Surface plasmon polaritons (SPPs)between the metal layer and slot layer are used to confine the opticalpower within a small dielectric gap. Compared with traditional phaseshifter based on silicon waveguides, the proposed CGD phase shifterhave two desired features: firstly, the CGD waveguide combines theoptical waveguide and metal electrode together to achieve a compactfootprint. However, in traditional modulators these two parts areisolated. Secondly, nonlinear polymer is used in the structure to realizeelectro-optic modulation and thus eliminating the carrier effect insidethe doped silicon region which limits the modulation bandwidth.Besides, the modulation performances and fabrication processes arealso demonstrated.3) We experimentally demonstrate a push-pull optical nonreciprocal transmission (ONT) mechanism induced by thermo-optic effect incascaded silicon microring resonators (MRRs). With thermo-optic (TO)effect, the mismatched cascaded MRRs can achieve push-pull resonanceshifts for different input-signal directions. A nonreciprocal extinctionratio of up to27dB and an operation bandwidth larger than0.15nm areachieved in the proposed ONT system. The device can operate with aresonance mismatch between the two cascaded MRRs from0.14nm to0.55nm. The proposed ONT device could potentially find applicationsin optical diodes and bidirectional control of light in future on-chipall-optical information processing systems.