With the rapid growth of worldwide internet traffic in data centers and clouds, silicon photonics has been utilized to provide enormous data bandwidth and outstanding energy efficiency over electronics. Computing servers and storage servers that are connected by communication links are relying more on optical rather than electrical means mainly due to the high bandwidth and low power consumption requirements. However, there are still many challenges for integrating photonic devices on an electronic chip, such as high power consumption and size mismatch. This dissertation is mainly focused on solving two of the challenges. One of them is the efficient coupling of light into the sub-micron photonic devices. The other is about building Electro-Optic Modulators (EOMs) with an ultra-compact size, low power consumption and high bandwidth.
As for the first challenge, we investigate how to achieve efficient coupling from free space into nano-sized plasmonic slot waveguide using optical nano-antennas. Four types of nano-antennas−dipole antenna, Yagi-Uda antenna, antenna array, and bow-tie antenna−are designed to exhibit the capability of achieving high coupling efficiency. Furthermore, a plasmonic integrated circuit has also been designed and fabricated with these four types of nano-antennas. Direct and efficient optical coupling from an optical fiber into the plasmonic integrated circuit is demonstrated, and the couple-out efficiencies for these four nano-antennas are directly compared and evaluated.
As for the second challenge, two types of EOMs are reported, one being integrated with plasmonic slot waveguide and the other being built on a standard silicon-on-insulator (SOI) waveguide. The two modulators, which are designed and experimentally developed here, uniquely utilize the transparent conducting oxides (TCOs) whose Epsilon-Near-Zero (ENZ) effect has made plasmonic material combine with electro-optic modulation. Therefore, the modulators are capable of leading to brand new next-generation photonic devices. Both of the EOMs are in micron scale and have >70 nm optical bandwidth, large enough for WDM applications. These properties show that the unique utilization of plasmonics is indeed a viable proposition for future EO interconnect applications. Moreover, the second type of EOM has demonstrated a dynamic modulation speed up to 2.5 GHz driven by a small Vpp of merely 2V. These two types of devices can be utilized as on-chip high-speed and high-energy-efficiency optical interconnects