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
Stanford researchers create new special-purpose computer that may someday save us billions
21.10.2016 | Stanford University
New 3-D wiring technique brings scalable quantum computers closer to reality
19.10.2016 | University of Waterloo
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.
In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
24.10.2016 | Earth Sciences
24.10.2016 | Life Sciences
24.10.2016 | Physics and Astronomy