Dec 6, 2002
Nanotechnology for an agile optical network
We live in an Internet-driven society. The volume of data transported across communications networks continues to grow, forcing service providers to design, build, and add capacity to their systems. Optical networks are essential to meet these future communications needs. Today, scientists are using nanotechnology to create these necessary technologies and components. Ted Sargent discusses the role nano-scale science plays in creating an agile optical network.
If the fibre-optic transmission systems of the past decade advanced telecommunications, then the agile optical networks of the coming decade have the potential to revolutionize. Instead of maximizing one parameter – speed – future optical communications will need to be simultaneously sensitive and responsive to the competing needs of many users. Optical switches will route beams of light from different points of origin into the many different fibres, amplifiers, and nodes of the network. But a smart and sophisticated strategy is needed to bring order and reliability to this potentially chaotic environment. Nanotechnology may, through new functions, offer the path to harmony.
For the past ten years, the number of bits of information which can be communicated over a fibre-optic link per unit time – its transmission capacity – has grown at an astonishing rate. This growth, though, has been uni-dimensional.
Nanotechnology adds new dimensions and directions to the progress of networking using light. It harnesses new and fundamental physics, chemistry, and engineering to enable not just higher speeds, but new capabilities. This nano-scale science could exploit the ways in which matter organizes into regular shapes and structures to integrate many such functions onto a single chip. The diverse functional possibilities of engineering on the nanoscale may deliver a new agility to the optical network.
Physics into novel function: connecting electrons and photons
Nanotechnology has the capacity to probe the structure and composition of atoms, molecules, and materials. Scientists are now investigating the function of matter and its constituents.
The prospective power of combined functional and structural imaging in nanotechnology is brought out by comparison with the field of medicine. Before the advent of real-time imaging of blood flow inside a living patient, doctors relied on external observation and measurements of the internal structure to determine patients’ health. Without functional imaging, the two could not be directly correlated. Today, doctors can follow the path of the flow of oxygenated blood, and map out structure-function relationships in their patients.
Our research group has recently used a nano-sized probe to study the potential and flow of electrons in a laser emitting an intense beam of light. We have observed -- with nanometre resolution -- the detailed flow of electrons to and from the laser’s active region, and have witnessed how healthy lasers successfully concentrate electron flow into the active region, while electrons bypass the region in unhealthy lasers. Our team uncovered blockages to electron flow and has traced their origins to the early stages of laser crystal growth.
The work illuminates the inner workings of lasers whose performance is critical in building better networks. Fibre-optic communications systems, connecting buildings within a metropolitan area, demand lasers which convert electrons efficiently and rapidly into photons. With the aid of functional laser imaging, we can now diagnose and treat impediments to the efficient production of light.
Researchers are turning physics into novel function on many other fronts as well. One research thrust involves the controlled merging of electronic and photonic materials. Materials which control the quantum behavior of electrons must confine these particles to a few nanometres. Quantum dots, or boxes, do just this, since they have dimensions in the dozens of atoms.
In order to control the flow of photons, light must be confined to sizes more on the scale of a micrometre, or one millionth of a metre. Photonic crystals, tiny lattice-like structures that may be able to manipulate light waves just as semiconductors manipulate electrical current, are the prototype for such optical control.
Through a combination of new theory and experiments, our group recently combined engineering on both the electron and photon length scales. Collaborating with the University of Toronto’s Dr. Eugenia Kumacheva and her research group, we have grown nanometre-sized quantum dots on the surfaces of micron-sized polymer spheres, and have induced the spheres to organize into regular arrays. Recent developments predict that these structures can enable functions urgently needed in the optical network – in particular, switches which automatically limit the power on an optical signal to a safe level, and which can restore and recalibrate optical pulses that have traveled over different distances. A dynamic optical network urgently requires components which can stabilize the network and groom the optical signals which it conveys.
Chemistry for integration: planting the seeds to orchestrate growth
The agile optical network needs not only new and complex functions. It needs to combine the monitoring and control of many disparate optical signals onto a convenient platform. Optical integration, wherein many different devices and their associated functions are conveniently combined on a planar substrate, could do for agile optical networks what the electronic integrated circuit did for computing; it could create the foundations of a technology which grows in performance and decreases in cost.
Photonic crystals could be a platform technology for optics just as silicon chips are for the electronic integrated circuit. The crystals allow scientists to control the flow of light. While researchers have been successful in creating a stable photonic crystal, they need to be able to control its placement, order, and configuration on the surface of materials.
Our group recently showed that we could specify how photonic crystals grow on a glass or silicon substrate, determining the pattern of crystal growth or its absence. We also discovered that the shape and size of the openings in their templates governed the properties of the crystals – whether they organized themselves according to square or hexagonal symmetries. These symmetries determine which wavelengths of light will be trapped and which ones will flow inside photonic crystals. Controlling this flow is the basis for developing a successful photonic circuit.
Four roads converged in the forest: chemistry and physics for information technology and medicine
Nanotechnology can do much more than enable a dynamic optical network. It creates an abundance of connections between biological and physical sciences and engineering. Living organisms are a triumph of the genesis of complex macroscopic structure and functioning of nano-sized genetic material. It is natural that humans should exploit the same principles to engineer technologies which harness new physics and chemistry in the service of applications in information technology and medicine. Through this nano-scale science and technology, people will obtain new scientific understanding and capabilities that will benefit all of society.
This article first appeared on EurekAlert!.
About the author
Edward (Ted) Sargent holds the Nortel Networks – Canada Research Chair in Emerging Technologies at the University of Toronto, Ontario, Canada.