It began like an ancient riddle. The young visionary goes to the master builder and asks the seemingly impossible: "Make me a house that's full of windows, but from which light cannot escape." The builder laughs, but is intrigued by the dreamer's vision. "How could it be possible?," he asks. "Build it as perfectly as an opal," replies the seer, "and make it from the world's most abundant material, silicon, and you will trap light. And more than that," he says enticingly, "you will control it."
The visionary of this tale is theoretical physicist Dr. Sajeev John, while the master builder is materials chemist Dr. Geoffrey Ozin. Together, the University of Toronto professors created the world's first photonic crystal capable of caging light, a major step on the road to optical microchips operating at the speed of light.
But beyond this singular breakthrough the researchers have formed a rich and enduring collaboration across disparate realms of science, an achievement for which they've been awarded the inaugural Brockhouse Canada Prize for Interdisciplinary Research in Science and Engineering.
Dr. John had travelled the world for a decade lecturing about his revolutionary idea of trapping and channeling light in a tiny silicon crystal lattice, all the while trying to get someone to take up the challenge of building the structure.
He first glimpsed the idea in the mid-1980s as a Ph.D. student. Electrons and photons both behave as waves. We're able to localize electrons, to control where they flow in everything from power lines to microchips, so would it be possible to trap a photon moving at 300,000 kilometres per second? Yes, believed Dr. John. What it required was to create a perfectly sized structure from silicon so as to create a photonic band gap, a region in which, because of its size, wavelengths of light couldn't travel.
"As it turns out, it is much more difficult to localize light than electrons," says Dr. John.
That's an understatement. Dozens of scientists around the world told him it was impossible. Nonetheless, the theoretician persisted, and in August 1998 went looking for the builder in his own backyard. Dr. John crossed the University of Toronto commons between the Physics and Chemistry departments and went to see Geoffrey Ozin.
"I was the perfect person to do the experiment," says Dr. Ozin.
For almost 30 years the materials chemist had dedicated himself to making synthetic structures of perfectly controlled size, shape and function. But most importantly he was a world-leader in making these structures porous, full of molecule-sized holes like a perfectly symmetrical block of Swiss cheese. Known as zeolites, these materials are the basis of a billion-dollar industry as separators and, due to their large surface area, as catalytic surfaces. He was one of the few scientists to have made nano-sized silicon into zeolites.
But, recalls Dr. Ozin, the light cage idea was completely different. For one, it was at a much larger scale – microns (the wavelengths of light) instead of nanometers (the size of the molecules used to make zeolite holes). And this wasn't about controlling a chemical reaction, it was about controlling light, a foreign concept at the time to the materials chemist.
Yet, something in that first meeting clicked. Whereas others had said it was pie-in-the-sky, Dr. Ozin laughed with some appreciation of the beauty of the idea. A year later, Dr. Sajeev John returned with a proposition too tempting to refuse. He'd coaxed the perfect template for his light cage, a synthetic opal of silica, from Spanish colleagues.
Within months, Dr. Ozin used his zeolite science skills to create the world's first silicon-based inverse-opal material. And, as their paper in Nature described, the material did indeed trap light, causing it to pulsate back and forth within the crystal at a quadrillion times a second (a quadrillion is a million billion, or 1 followed by 15 zeros).
It was 1999, the peak of the telecommunications boom, and the discovery caused an enormous wave of excitement and expectation as the basis for the creation of insanely fast optical microchips in which the movement of light could be tightly controlled.
Since then it's become clear, says Dr. Ozin, that bringing the concept from demonstration of proof-of-concept to an engineered optical chip component will be more challenging than many first imagined. So he and Dr. John have continued to explore ways to make photonic band gap materials more efficiently and how to extend this to the design and fabrication of optical chip components, including three-dimensional ones.
"It's very, very rare to get this kind of complementarity and to take it to a very high level on a very hot topic with a breakthrough and then stick together," observes Dr. Ozin.
For the past five years the two scientists have regularly shared a lunch table at the University of Toronto's Faculty Club, beating around ideas for next steps into the unknown. "Sajeev is the guru," says Ozin, adding that he proposes a bevy of possible routes, most of which his table mate rejects out of hand on theoretical grounds (avoiding the time and cost of hit-and-miss chemistry), but then runs with the one idea in ten that has theoretical potential. In part inspired by these conversations, Dr. Ozin has extended the possible use of photonic crystals into the realm of structure-based colour. In collaboration with industry partners, his lab is working on creating coloured photonic ink and optical chromatography.
"He's a very clever materials chemist," says Dr. John of his colleague. "He has a certain boldness, and we're not afraid to express our ignorance to one another."
And why does the collaboration work so well? "To work it's got to be like a marriage, full of mutual respect and trust," says Dr. Ozin. And above all, they say, it's based on good communication.
"We come from very different scientific backgrounds. The last common course we took was probably in first year university," says Dr. John. "Often people like that don't understand one another perfectly well."
However, Dr. Ozin notes that, "(Dr. John) is able to communicate very complex issues in a sufficiently simple way that a practising synthetic chemist like myself can come to terms with it."
They both emphasize that interdisciplinary research of the kind they're pursuing is now essential to the discovery process in many sciences, including nanoscience, since the insights sit at the boundaries of disciplines. They've created an interdisciplinary graduate seminar to help foster this boundary land exploration.
"People in general are very reticent to go outside of what's familiar to them," says Dr. John. "I think it's important to encourage that more and more. I think more exciting discoveries will be made that way."