European research on materials known as photonic crystals has made important progress in the race to build all-optical chips for computers and communications systems. The scientists developed a relatively inexpensive way to make high-quality photonic crystals, and showed how these can be integrated into conventional silicon chips.
Photonic crystals are materials whose optical properties vary in a regular, repeating way on a scale of a few hundred nanometres. An ideal photonic crystal can be designed to transmit light of one particular wavelength, and to block all other wavelengths. This gives photonic crystals some very useful properties.
The simplest material of this kind has a layered structure, like a film of oil on water. ‘One-dimensional’ structures like this are used as mirrors, non-reflective coatings, and paints whose colours change with the viewing angle. The gemstone opal, with its shimmering colour, is a natural photonic crystal.
The PHAT project worked with more complex structures whose optical properties vary in two and three dimensions (2D and 3D). Two-dimensional photonic crystals can act as waveguides, channelling light to where it is needed, and as filters to separate different wavelengths – a valuable property in optical communications. Three-dimensional photonic crystals can even trap light within their structures, potentially allowing them to act as optical switches.Shrinking silicon
Communications technology has been revolutionised by electro-optical devices based on the semiconductors gallium arsenide (GaAs) and indium phosphide (InP), optical fibres, and even all-optical amplifiers. But as PHAT spokesperson Gudrun Kocher points out, these devices tend to be much larger than the components needed to make computer chips. GaAs and InP are also expensive materials, and integrating them with silicon brings extra complexities. As a result, she says, most researchers agree that it will be 10-15 years before we see all-optical chips based on conventional (silicon) technology.
This is where photonic crystals come in. A combination of 3D photonic crystal optical switches and 2D waveguides could yield devices that are 10 or even 100 times smaller than those made at the moment. These could be used to assemble all-optical chips made entirely from silicon.Mix and pour
Beads of plastic (PMMA) or silica, 250-900 nm in diameter, are first mixed with water to form a colloidal suspension. Then a solid surface is drawn slowly out of the water, and the beads stick to it in a regular lattice structure. The PHAT team assembled their ‘artificial opals’ by allowing capillary forces to draw the beads along microscopic channels cut in sheets of silicon or silica. In a single dip, they were able to form layers up to 10 mm long and more than 10 beads deep – the minimum practical thickness for a 3D photonic crystal.
The resulting structure of beads separated by air is known as a ‘direct opal’. The resulting refractive index is too low for many applications, so a subcontractor in St. Petersburg used chemical vapour deposition (CVD) to fill the empty spaces with silicon, after which the beads themselves are removed, leaving holes.
A further task was to use electron beam lithography to create a defect layer in the 3D crystals. “That’s because if the crystal is perfect, there’s no way to get light into or out of it,” Kocher explains. Finally, the plan is to sandwich two 3D crystals around a 2D crystal to act as a waveguide.
PHAT was coordinated at the Tyndall National Institute in Cork, Ireland, and had four other partners: the French Atomic Energy Commission (CEA) and University of Montpellier II, Mainz University, Germany, and the Technical Research Centre of Finland (VTT). “This was an ambitious project, and we didn’t manage everything that we set out to do,” says Kocher.
But by the time the project ended, in February 2007, it had two really big achievements under its belt. “We had developed a spatially-selective method of growing photonic crystals, and we had managed to integrate 3D photonic crystals with waveguides, which was a first,” says Kocher.
The crystal fabrication method was patented by two of the project partners, Tyndall and VTT. “This was a significant advance in photonic crystals, and it brings us a step closer to a practical optical computer, ” concludes Kocher.
Christian Nielsen | alfa
Powerful IT security for the car of the future – research alliance develops new approaches
25.05.2018 | Universität Ulm
Supercomputing the emergence of material behavior
18.05.2018 | University of Texas at Austin, Texas Advanced Computing Center
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences