Power/Performance Bits: July 6

Configurable photonics
Researchers from the University of Southampton developed a configurable/one-time programmable silicon photonic circuit that could reduce production costs by allowing a generic optical circuit to be fabricated in bulk and then later programmed for specific applications such as communications systems, LIDAR circuits or computing applications. Additionally, once programmed, its signal routing is retained without the need for additional power consumption.

“Silicon photonics is capable of integrating optical devices and advanced microelectronic circuits all on a single chip,” said Xia Chen from the University of Southampton. “We expect configurable silicon photonics circuits to greatly expand the scope of applications for silicon photonics while also reducing costs, making this technology more useful for consumer applications.”

“The technology we developed will have a wide range of applications,” said Chen. “For example, it could be used to make integrated sensing devices to detect biochemical and medical substances as well as optical transceivers for connections used in high-performance computing systems and data centers.”

The new work builds on earlier research in which the investigators developed an erasable version of an optical component known as a grating coupler by implanting germanium ions into silicon. These ions induce damage that changes silicon’s refractive index in that area. Heating the local area using a laser annealing process can then be used to reverse the refractive index and erase the grating coupler.

The researchers applied the same germanium ion implantation technique to create erasable waveguides and directional couplers, components that can be used to make reconfigurable circuits and switches. They say this represents the first time that sub-micron erasable waveguides have been created in silicon.

“We normally think about ion implantation as something that will induce large optical losses in a photonic integrated circuit,” said Chen. “However, we found that a carefully designed structure and using the right ion implantation recipe can create a waveguide that carries optical signals with reasonable optical loss.”

They demonstrated the new approach by designing and fabricating waveguides, directional couplers and 1 X 4 and 2 X 2 switching circuits, using the University of Southampton’s Cornerstone fabrication foundry. Photonic devices from different chips tested both before and after programming with laser annealing showed consistent performance.

Because the technique involves physically changing the routing of the photonic waveguide via a one-time operation, no additional power is needed to retain the configuration when programmed. The researchers have also discovered that electrical annealing, using a local integrated heater, as well as laser annealing can be used to program the circuits.

The researchers are working with ficonTEC to make this technology practical outside the laboratory by developing a way to apply the laser and/or electrical annealing process at wafer scale, using a conventional wafer prober, so that hundreds or thousands of chips could be programmed automatically. They are currently working on integrating the laser and electrical annealing processes into such a wafer-scale prober being testing at the University of Southampton.

Shrinking photonics
Researchers at the University of Sydney and Friedrich Schiller Universität Jena combined traditional chip design with photonic architecture in a hybrid structure to shrink the size of photonic chips.

“We have built a bridge between industry-standard silicon photonic systems and the metal-based waveguides that can be made 100 times smaller while retaining efficiency,” said Dr Alessandro Tuniz from the University of Sydney Nano Institute and School of Physics.

The team’s design utilizes hybrid plasmonic elements based on off-the-shelf silicon-on-insulator waveguides. The plasmonic ICs consist of a plasmonic rotator and a nanofocusser, which generate the second harmonic frequency of the incoming light. This compresses the light and allows for manipulation of information at the nanoscale, 100 times smaller than the wavelength of light carrying the information.

“This sort of efficiency and miniaturization will be essential in transforming computer processing to be based on light. It will also be very useful in the development of quantum-optical information systems, a promising platform for future quantum computers,” said Stefano Palomba, associate professor at University of Sydney and Nanophotonics Leader at Sydney Nano. “Eventually we expect photonic information will migrate to the CPU, the heart of any modern computer. Such a vision has already been mapped out by IBM.”

“As well as revolutionizing general processing, this is very useful for specialized scientific processes such as nano-spectroscopy, atomic-scale sensing and nanoscale detectors,” said Tuniz.