Apr 7 (Wed): "Monolithic Passive-active Integration of Epitaxially Grown Quantum Dot Lasers," Zeyu Zhang, ECE PhD Defense

https://ucsb.zoom.us/j/81008715558?pwd=SHRwODBZTnNDVkhnekt0VkdpbysyUT09

ABSTRACT:

The age of the Internet brings unprecedented challenges to the communication networks. The ever non-stopping increase of link traffic in data center demands wide bandwidth, densely integrated yet low cost optical transceiver circuits. For on-chip communication, copper interconnections are increasingly challenged by the stringent link budget presented by today's multi-core processing units. As an alternative, On-chip optical interconnect is being actively pursued due to its energy efficiency and scalability. Addressing these challenges brings photonic integrated circuit closer and closer to the processing electronics. Si photonics will undoubtedly be the key to achieving such feat due to its CMOS compatibility and its ability to offer compact, low-loss, and versatile photonic circuitry. Yet, silicon, being a non-direct bandgap material, need to be integrated with III-V material to create on-chip light source. One of the approaches to achieve this is by epitaxially growing quantum dot laser stack on silicon substrate.

Over the past few years, we, together with our colleagues around the world, have made significant improvements in the material quality of the epitaxially grown quantum dot lasers. Yet, little efforts have been taken in integrating the grown quantum dot material with passive waveguide structures.

In this dissertation, we first dive into the gain characteristics of the quantum dot laser material. A novel measurement technique is adopted to allow studying the unique properties of quantum dot active region under the influence of different growth techniques. Such knowledge provides insights on how to further improve the performance of quantum dot lasers. With sufficient understanding of the quantum dot material, we designed a novel device platform which enables integration of quantum dot active region with passive waveguide structure. By doing so, complex laser cavities such as DBR lasers, mode-locked lasers, and SGDBR tunable lasers are demonstrated in this platform. The same laser stack can be easily grown on the substrate of a silicon photonic chip to allow light coupling from the III-V laser cavity to the silicon waveguide.

BIO:

Zeyu Zhang is a PhD candidate in Prof. John Bowers group.

Hosted by: Professor John Bowers

Submitted by: Zeyu Zhang <z_zhang@ucsb.edu>