Doctoral research project

Person in charge of the project:
DE MEYER CHRISTINA, member of research team Associated Section of ESAT - INSYS, Integrated Systems
CMOS Circuitry for Low Power Ring-based Silicon Photonics Optical Link
Project summary:
In the near future, Tb/s-class aggregate bandwidth input/output (I/O) circuits will be needed for high-end performance computing systems. A high-performance I/O using optical transmission technology is being considered to overcome the limitation of a conventional electrical I/O in termsof data rate per channel, a bandwidth per millimeter and power consumption.A silicon photonics technology is very promising candidate to realized Tb/s-class aggregate I/O bandwidth with improved energy efficiency targeting cost-effective short-range optical links. Silicon photonics offers many unique advantages such as the transparency of silicon at telecom wavelengths and a very high index contrast between a silicon and its oxide. This high contrast enables optical modes to be confined and guided in a small footprint silicon waveguide combined with a very low optical loss. To convert an electrical data stream into the optical domain, silicon photonics can offer a broad selection of different types of optical modulators. One of the most promising modulators is the micro ring modulator, which, thanks to a very small footprint and a low control voltage, can ensure fast and energy efficient optical modulation. High speedoptical detection and conversion back to the electrical domain can alsobe efficiently realized in this technology by taking the advantage of germanium waveguide photodiodes with high responsivity. Finally, the fabrication of silicon-based photonic circuitry with the existing CMOS infrastructure can potentially translate into a higher yield and a lower costat high volumes.To enable high speed and low power optical link, the silicon photonics devices must interact with an energy efficient CMOS control circuitry. The focus of this dissertation is put on the design and demonstration of low power and high speed CMOS circuits to control the photonic devices. In order to efficiently transmit data by modulating an optical beam, a novel concept of driver circuit is presented. The driver is able to provide a differential signal with a voltage swing higherthan the power supply voltage in order to maximize the optical modulation amplitude and minimized the insertion loss. Low power and efficient data conversion from the optical to the electrical domain on the receiverside of the link is demonstrated with low noise and high speed transimpedance amplifier (TIA).Low power and efficient data conversion from the optical to the electrical domain on the receiver side of the link isdemonstrated with the use of a low noise and a high speed transimpedance amplifier (TIA). The proposed architecture of the TIA allows for a sufficiently high gain and bandwidth even when using a low supply voltage CMOS technology node.The design of the CMOS circuitry is verified through two demonstrators, which validate the design and the architecture concept. The flip-chip integrated CMOS die on top of co-design silicon photonics chip allow to demonstrate optical transmission at 10Gb/s and 20Gb/s with very competitive when compared with the stage-of-the-art results. The optical link energy efficiency and demonstrated bandwidth provingthat this technology in a near future will seriously compete with the electrical chip-to-chip interconnect solutions.
ph.D student :
Faculty of Engineering Science
Doctoral Programme in Engineering Science (Leuven)

ph.D defence : 27.11.2014
Full text ph.D