A few photons are enough
When the current electronics technology cannot meet the rapidly expanding needs of data communication, light comes to the rescue. A research group at TUT is developing light-based technologies and enabling applications that, until now, have been little more than dreams.
Professor Mircea Guina presents a photograph showing microscale light sources incorporating quantum-dot emitters.
Professor Mircea Guina has a sip of espresso and presents graphs and figures that illustrate the work his team has carried out at the Optoelectronics Research Centre over the past few years. One of the main interests of his group has been to explore the possibilities of photonics in advancing – and eventually, in certain applications, even replacing – the current silicon-based electronics technologies.
The age of the current silicon-based microelectronics is coming to an end. Nanofabrication techniques have developed to the point that electronic circuits can be incredibly densely-packed with extremely small devices and conductors, but further progress along this well-known path is facing a wall due to problems related to losses and power consumption. Guina points out that even at the current size scale, using metal conductors for transferring high-rate data on an electronic integrated circuit creates a lot of heat, which is detrimental to devices and consumes significant amounts of energy. In any case, increased communication speed is by default associated with increased power consumption.
Light is already commonly used for data transfer. The modern internet relies heavily on light pulses that travel in optical fibres. Rather than using light to link buildings and continents, Guina is interested in using it for the basic functions of an integrated device, just as electrons are used in current microelectronic devices.
“Our goal is to replace electrons with photons. We can already fabricate hybrid components, which combine light-emitting devices and silicon-based circuitry. However, there are still many challenges, such as achieving the necessary accuracy for aligning the different components with one another.”
In Mircea Guina’s illustrations, light travels in silicon waveguides trapped in a microscopic labyrinth. Using indium phosphide as the light-emitting material is the most common approach utilised by big companies like IBM, Intel, and Toshiba. However, Mircea Guina has chosen a different path: he uses materials based on gallium arsenide and gallium antimonide.
“We wanted to try a different approach for light generation and integration to silicon passive circuits, which turned out to be a good choice. Our materials can produce new wavelengths, which enables new applications and brings more functionality,” Guina explains.
Getting smaller and smaller
The problem of hybrid integration is that the photonic integrated circuits cannot be shrunk into small enough size. The solution to this could be monolithically integrated light sources. Since silicon cannot emit light, the typical solution is to cover it with a thin layer of light-emitting material.
“This step towards monolithic integration is crucial. It enables the miniaturisation of photonic circuits similar to how electronic integrated circuits have been shrunk down. This would mean significant progress in data transfer, fabrication, and a number of other areas.”
The latest research topic of Guina’s group in the field of photonic integration is light-emitting III-V semiconductor nanowires. These nanowires can be grown directly on a silicon surface and they can produce small quantities of photons very efficiently – in theory, at least.
“Light-based data transfer busses and waveguides have much smaller signal losses than current electronics. Thus, even a little bit of light is enough. Devices get smaller, more stable, and consume less energy.”
Taking things to next level
European Union has selected photonics as one of the five future technologies that have the highest potential to have significant financial and societal impact. The technologies developed by Guina’s group are currently being used only in rare applications due to their high price and low availability, but the market will only grow with the advances in research and development.
“We plan to start up a commercialisation project running in parallel with the basic research on photonic integrated circuits. This project will survey application possibilities in medicine, mobile technology, and sensing.” Mircea Guina estimates that the opportunities new light-based photonic integrated technologies offer in these fields will potentially have a big impact on national economics.
“In the beginning, it was difficult to get funding for this topic because the advantages offered by our approaches were not immediately obvious. Now many other groups are interested in our materials, but we already have a head start of several years.”
Science takes more than two to tango
Photograph of a photonic integrated circuit (PIC) for data communication showing arrays of optical amplifiers developed at ORC and mounted on top of passive silicon circuitry at VTT (Silicon Photonics group led by Dr Timo Aalto). Results obtained in FP7 project RAPIDO.
Mircea Guina’s research group works closely with VTT’s Silicon Photonics group. VTT’s knowledge in silicon platforms combined with TUT’s expertise in photonics has already resulted in several research projects. The group is running their third large EU project (MIREGAS http://www.h2020-miregas.eu) on this topic, and a fourth one is already on the drawing board. Altogether, the group has received nearly €5 million in EU funding in this field.
“VTT is a top-level player in the fabrication of silicon waveguides,” Mircea says.
“The level of integration of different material groups is a decisive factor in terms of the future of optoelectronics. Advancing the integration by joint efforts opens new possibilities,” Guina says.
In addition to the collaboration with VTT, Guina is thankful for his tightly woven research team, the members of which have grown into top-level professionals in the field.
“In science, it takes more than two to tango. Achieving harmony between different people and ideas makes for beautiful results.”