November 30, 2010

The Scientist: Michal Lipson

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The observation and understanding of light in nature led to inventions of new technology and fields of science. Photosynthesis in plants inspired technologies to use sunlight as an alternative energy source. Light establishes an example of particle-wave duality, which contributed to the birth of the quantum mechanics. Light is the key matter in the theory of relativity. In reality, light is the fastest traveling matter on earth.

Prof. Michal Lipson, electrical and computer engineering, is a leading researcher in the field of nanophotonics — the study of understanding and utilizing light on the nanometer scale. A nanometer is one-billionth the size of a meter, and it is used frequently to describe the wavelength of light.

Light’s ability to travel quickly and efficiently gives it the potential to be the ideal medium to process data in electronic devices. In her laboratory, Lipson develops nanophotonic circuits that can be used compatibly with the current microelectronics in a single chip.

The quality and the speed of performance for the electronic devices greatly depend on the microprocessor, which incorporates the major functions of the central-processing-unit in a chip.

The current microprocessor only consists of the electronic components, such as diodes, transistors and MOSFETs. The advanced microprocessors, such as those used in personal computers and laptops, contain billions of transistors. The main drawback of the current microprocessor is that these transistors require large amounts of power to propagate data, which limits the amount of data and the speed at which they are processed.

“In the future, when you open up the chips, it won’t only have the electronic components but it will also have the optical components. Using optics to transfer data, the computers will be able to propagate more data at much lower power,” said Lipson.

Integrating optical components into the electronic components is not trivial. Most electronic components are made of semiconducting material, such as silicon, but silicon has poor optical properties.

Lipson exploited a way to change the optical properties of silicon by injecting carriers — charged particles that conduct electricity — into it.  Semiconductors, like silicon, conduct electricity using electron-hole pair. Based on the free-carrier plasma dispersion effect, the injection of carriers can change the refractive index of silicon. Refractive index is an optical property of a material which measures how fast the light propagates in it. This process increases the efficiency of light propagation between the optical components and the electronic components.

When embedded together, these two types of components need a way to communicate. This requires photonic circuits that can do various tasks, such as modulating, detecting and switching the light signals. Her group is one of the first to work with silicon to design and prototype these components.

For example, Lipson and her group members previously demonstrated that their silicon electro-optic modulator can transmit light at 18 Giga bytes per second. In comparison, commercial hard drivers process data at three to six Giga bytes per second.

According to Lipson, preliminary computer simulations showed that this could also decrease the power consumption of the electronic devices by an order of magnitude.

“As a result of our work, we expect to have the future supercomputer on a little chip,” said Lipson.

The impact of Lipson’s work in nanophotonics is evident in many ways. Her work appeared in leading academic journals, and has been cited over 100 times. She owns a number of patents, and she aims to start a company.

Recently, she was named as one of the MacArthur Fellows of 2010. The award exemplifies the innovation and potential impact of scientists, writers, artists, social scientists, humanists, teachers and entrepreneurs.

Among all the awards and honors, said Lipson, she is most flattered when her children recognize them. “It feels amazing when my son tells me about my award; that everyone in school knew that Ethan’s mom won the MacArthur award.”

Original Author: Eugene Choi