The Need for Photonic Integration

This wiki is largely drawn from a presentation by Larry Dalton delivered July 21, 2008. The steaming version of the persentation is available here.

One of the things that we all face as scientist is deciding what topics we want to pursue for our research career. Two things are useful one is the professional society which hold special symposia on hot topics such as high temperature super conductivity. An ever better avenue is that funding agencies hold workshops on emerging topics. In 2007 both the NSF and the Defense Science Board which make recommendations for defense spending, held workshops on photonics integration. So this is perceived as a hot research topics.

Types of photonic integration

There are two type of photonic integration. Type one refers to simply taking the photonic devices such as lasers, modulators and optical circuitry and attaching it by conventional means like wires and fibers to electronic technology. Type two is the more exciting aspect ,that is actually photonic and electron function on the same chip.

Particles suitable for telecommunication

In the universe there four types of particles involved in the communication of information.

Electrons—Negatively charged particles and the lightest of the three particles (electrons, protons, and neutrons) that make up atoms. The electron is most easily perturbed by the application of an electric field. If you take an single atom the energy levels are quantized. The highest occupied orbital is bound state so electrons are localized. But in metals, electrons in the highest occupied band conists of electrons that are not tightly bound to any specific atom known as the conduction band. That movement can be used convey information.

Photons—The smallest (quantized) units of light.

Phonons—Quantized vibrations or quantized sound waves however these are short ranged so we will ignore them. We have convert phonons into electrical or optical signals in order to convey them over distance.

Plasmons—Quantized waves in metals excited by light. These are short ranged so we will ignore. They are useful for engineering extremely small scale circuits connected by nanowires carrying plasmons.

Trends for Data in Telecommunications

Signaling with Mance heliograph, 1910

The history of modern telecommunication by wire and wireless dates back to the telephone in which we transduce the phonon vibrations of the human voice into electrical signals that were carried over copper wire. The wireless telecommunication date back to the heliograph which uses mechancial modulation of light. These original devices had very limited bandwidth because you could only run a shutter so fast. Copper wire was ok for the amount of data that a voice stream demands. Telecommunications has evolved to involve "machine-to-machine" telecommunications. This has placed dramatically larger demands on bandwidth– the amount of information we send per unit time. We also want more capability in smaller and smaller devices. Copper has given away to optical fiber. Wireless frequencies has extended to 100 gigahertz carriers, eg gGigabeam inc. You only have to look at the advertisements for bandwidth and integration for consumer devices to release how important these have become as drivers.

Moore’s Law- the History of Integration

Nano-engineering has been around for a long time. For example silicon CMOS technology has built smaller and smaller transistors and placed more transistors on a chip. Moore’s law shows feature size decreasing over the years and has allowed us to place 10 billion transistors on a chip in 2010 with a bandwidth of 30 GHz. This has resulted in a great reduction in cost. You can buy a computer today for about the same cost as 30 years ago but the functionality has exponentially increased. Tools such as reactive ion etching (RIE) and e-beam lithography have enabled nano-engineering.