UC Berkeley

Spontaneous Emission Rate Enhancement Using Optical Antennas

by Nikhil Kumar

Doctor of Philosophy in Engineering - Electrical Engineering and Computer Sciences University of California, Berkeley

Professor Eli Yablonovitch, Chair

The miniaturization of electronics has relentlessly followed Moore's law for the past several decades, allowing greater computational power and interconnectivity than ever before. However, limitations on power consumption on chip have put practical limits on speed. This dissertation describes the role that optical antennas can play in reducing power consumption and increasing efficiency and speed for on-chip optical interconnects.

High speed optical communication has been dependent on the laser for its narrow linewidth and high modulation bandwidth. It has long outperformed the LED for both practical reasons and very suitable physical characteristics. Lasers however have some downsides when considering short distance communications which may not require narrow linewidths. Typically, they require high powers, take up more space and the rate is inherently limited by gain saturation. Light Emitting Diodes (LEDs) on the other hand are limited by spontaneous emission, a rate that is dependent upon its electromagnetic environment. The use of metallic optical nano-antennas can significantly increase a light emitters coupling to its environment and potentially achieve a rate orders of magnitude faster than stimulated emission. Coupling a light emitter into an efficient nano-optical antenna serves three purposes - 1) a much faster modulation speed can be achieved due to a faster rate of spontaneous emission, 2) the footprint of such a device would be shrunk to the nano-scale, ultimately necessary for large scale integration and 3) the overall efficiency of the emitter can be increased.

While the main motivation behind this work is for short distance communications, optical antennas can serve in a host of applications including photodetectors, solar cells, nano-imaging, bio-sensing and data storage.

In this thesis we derive the theory behind optical antennas and experimentally show an enhanced spontaneous emission rate.