UC San Diego

Data explosion generates huge data traffic within the data center. The bottleneck of the data transportation is the optical transceiver. We study the critical component in the optical transceiver- optical modulator. The Figure-of-Merit (FOM), 3dB bandwidth/ V_π defines the modulation efficiency. In this dissertation, two approaches will be presented: 1. Utilizing GaN nano-pillars as electro optic material. GaN nano-pillars exhibits high second harmonic susceptibility, χ^((2)), which is proportional to the electro-optic coefficient. 2. A new design of the optical modulator: nano-slot conductive waveguide directional coupler modulator (DCM). The DCM modulation performance evaluation is based on Beam Prop mode simulation analysis. Using the 50Ω terminated lumped-element to calculate the 3dB bandwidth, the DCM shows a FOM of 202 GHz/V where the state-of-the-art silicon-organic hybrid (SOH) Mach-Zehnder modulator (MZM) is 150.3 GHz/V. The advantage of applying DCM as the modulator platform for high EO coefficient polymer is not only the DCM has higher modulation FOM, but also the ease of the modulator design and fabrication. The DCM does not require two phase shifters, Si waveguide to polymer slot waveguide couplers, and multi-mode interferometer (MMI). To prove the principle of the strong cross-coupling characteristic in DCM, we design and fabricate an air-slot, non-slab DCM, which includes the input/output mode size converter, adiabatic S-bend, and the air-slot waveguides. By scanning the central wavelength of the incident light, the output power collecting from each of the two ports exhibits wavelength dependence. The extinction ratio is ~10 dB and the peak-to-valley separation is ~1 nm. The measurement result matches with the Beam Prop simulation.