Bright future for optical devices

Physicists at the University of Toronto have created a blueprint for a photonic crystal that may pave the way for better, faster and perhaps unprecedented optical devices.

Physics professor Sajeev John and graduate student Ovidiu Toader report that they have created a blueprint of a three-dimensional photonic bandgap crystal that opens a new door for the development of devices like all-optical micro-transistors, optical wavelength converters and other components for optical microchips.

‘In terms of making a material that’s three-dimensional with a large photonic bandgap, there’s been a bottleneck in the field over the past 10 years,’ said John. ‘Other types of designs or blueprints for large photonic bandgaps have been created but their production is so complex or time consuming that for all intents and purposes they are commercially unusable. Our blueprint can be mass-produced at a very low cost, and that’s the crux of the matter.’

Light is currently used in fibre optic cable as a super-efficient transmitter of information; in concentrated form, it is also used as laser beams to perform delicate surgery or scan compact discs or bar codes. John and Toader’s new blueprint allows optically based technology to be carried to the microscopic level.

The physicists say their design should come as a surprise to fellow scientists who didn’t believe it was possible.

‘People thought that to cover a broad wavelength range, photonic bandgap materials had to resemble a diamond lattice,’ explained Toader. ‘But diamond structures are very difficult to make because they have very intricate three-dimensional designs. In the past, scientists tried to mimic the diamond structure with something called the ‘woodpile’ structure – looking something like a stack of Lincoln logs – but they are extremely arduous to make. The structure must be grown one layer at a time, and after several years of work, they’ve only managed to grow about eight layers.’

The photonic bandgap crystal design created by John and Toader is based on a tetragonal lattice, like a cubic lattice with spiralling posts that are stretched in one direction. They say it is much easier to make and can be done by a micro-fabrication technique known as glancing angle deposition (GLAD), which grows the spiralling posts in a one step process.

‘Photonic bandgap crystals can do most of the functions required in telecommunications,’ said John. ‘It allows you to control the flow of light through passive optical devices, but also create active devices that no one has ever made before like micro-transistors. This could affect not only telecommunications but also the computing industry.’