Eli Yablonovitch sheds light on photonic crystals in Newton Lecture

9 November 2015

An effect discovered more than a century ago has led to modern devices for manipulating light and spawned research into applications that could surpass lasers in optical communications, Professor Eli Yablonovitch said in this year’s Isaac Newton Lecture.

Eli Yablonovitch

Yablonovitch was invited to give the lecture at the IOP’s London centre on 6 November as winner of the Institute’s 2015 Isaac Newton Medal and Prize. He is Professor of Electrical Engineering and Computer Sciences at the University of California, Berkeley, and was awarded the prize for “his visionary and foundational contributions to photonic nanostructures”.

Yablonovitch explained that Lord Rayleigh showed in 1887 how electromagnetic waves propagating through a periodic structure would experience reflection and distortion, with light of certain wavelengths passing through while other wavelengths would be stopped, creating “photonic bandgaps”. Rayleigh had described how this would operate in one dimension, but extensive research in two and three dimensions did not take off until the 1980s, when Yablonovitch and others worked on building nanostructures with these properties.

Such nanostructures, which he had named “photonic crystals”, had been found to be common in nature, he noted. They were responsible for effects such as the iridescence of some beetles’ wings, the ability of chameleons to change colour and, as he illustrated with an amusing video clip, the colourful displays of birds of paradise. “We did eventually develop a structure that had a built bandgap, but it took years of trial and error,” he said. Even then, it was hard to suppress all spontaneous emission of photons, which was regarded as “undesired and parasitic”, he said.

The research had shown how it was possible to inhibit spontaneous photonic emission, but for some applications it would be useful to know how to enhance spontaneous photonic emission instead, he realised. This had prompted his research on optical antennas. “In the next year or two we are going to see tremendous enhancement of spontaneous emission through optical antennas – enhancement rates of 2,500 times, though with 50% efficiency, should be possible,” he said, enabling even faster communications than those based on lasers.

During questions, the IOP’s president, Professor Roy Sambles, asked how Yablonovitch was coping with the historical divide between engineering and physics, and whether he would agree that physicists needed to “wise up a bit”. Yablonovitch said: “Yes, but I won’t be popular for saying that. I was told that I was given the best physics education you can have, but when I came to start my own company, I realised that I knew nothing.”

Similar fields, such as the physics of information and signal processing, were known by different names in the two disciplines, while many new and interesting things had been discovered in applied maths that had not yet been applied in physics, he said.