Power/Performance Bits: July 28

Programmable photonics; speedy Internet; anti-counterfeiting with light.


Programmable photonics
Researchers from the University of Southampton developed a method for making programmable  integrated switching units on a silicon photonics chip. By using a generic optical circuit that can be fabricated in bulk then later programmed for specific applications, the team hopes to reduce production costs.

“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.”

Previously, the researchers developed an erasable version of the grating coupler optical component 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 team used the same germanium ion implantation technique to create erasable waveguides and directional couplers. Together, these components can be used to make reconfigurable circuits and switches. The work also 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.”

To demonstrate the approach, the researchers fabricated waveguides, directional couplers and 1 X 4 and 2 X 2 switching circuits at 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.

The technique physically changes the routing of the photonic waveguide, so no additional power is needed to retain the configuration. 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 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 researchers are working with ficonTEC to make this technology practical outside the laboratory by applying the annealing process using a conventional wafer prober.

Speedy Internet
Researchers from Monash University, Swinburne University, RMIT University, City University of Hong Kong, Xi’an Institute of Optics and Precision Mechanics, and INRS-Énergie Matériaux et Télécommunications recorded the world’s fastest Internet speed from a single optical chip.

The team managed a data speed of 44.2 Tbps from a single light source.

They used a new device that replaces 80 lasers with a single micro-comb, an optical component that is smaller and lighter than existing telecommunications hardware. Micro-combs create a rainbow of infrared light allowing data to be transmitted on many frequencies of light at the same time, vastly increasing bandwidth. It was planted into and load-tested using existing fiber-optic infrastructure, which mirrors that used across Australia’s National Broadband Network (NBN).

“We’re currently getting a sneak-peak of how the infrastructure for the internet will hold up in two to three years’ time, due to the unprecedented number of people using the internet for remote work, socializing and streaming. It’s really showing us that we need to be able to scale the capacity of our internet connections,” said Dr Bill Corcoran, co-lead author of the study and Lecturer in Electrical and Computer Systems Engineering at Monash University. “What our research demonstrates is the ability for fibers that we already have in the ground, thanks to the NBN project, to be the backbone of communications networks now and in the future. We’ve developed something that is scalable to meet future needs.”

The researchers installed 76.6km of ‘dark’ optical fibers between RMIT’s Melbourne City Campus and Monash University’s Clayton Campus. Within these fibers, researchers placed the micro-comb, which acts like a rainbow made up of hundreds of high quality infrared lasers from a single chip. Each ‘laser’ has the capacity to be used as a separate communications channel. Researchers were able to send maximum data down each channel, simulating peak internet usage, across 4THz of bandwidth.

The researchers say the technology has the capacity to support the high-speed internet connections of 1.8 million households in Melbourne, Australia, at the same time.

Reaching 44.2 Tbps showed the potential of existing Australian infrastructure, said Arnan Mitchell, Distinguished Professor at RMIT. “Long-term, we hope to create integrated photonic chips that could enable this sort of data rate to be achieved across existing optical fiber links with minimal cost,” Mitchell said. Initially, these would be attractive for ultra-high speed communications between data centers. However, we could imagine this technology becoming sufficiently low cost and compact that it could be deployed for commercial use by the general public in cities across the world.”

The team hopes to scale up the current transmitters from hundreds of gigabytes per second towards tens of terabytes per second without increasing size, weight or cost.

Anti-counterfeiting chip
Researchers from the University of Tsukuba, Leibniz Institute of Photonic Technology, Rikkyo University, and National Institute for Materials Science developed an anti-counterfeiting measure that uses the whispering-gallery effect to create a pattern that can’t be duplicated.

The team deposited small dye particles, where fluorescence from the particles can be turned on and off, onto a small microchip. They then selectively lit up the chip in a defined pattern with regions of bright particles and regions of dark particles.

Each dye particle has a unique diameter and shape. Thanks to the principles of the whispering-gallery effect, the fluorescence emitted by each particle is unique.

“Instead of using sound waves, we used light waves to follow the concave surface of micrometer-size dye particles,” said Professor Yohei Yamamoto of the University of Tsukuba. “This creates a complex color pattern that cannot be counterfeited.

“We attained a pixel density of several million per square centimeter on our optimized microchips,” said Yamamoto. “We have developed a high-security, two-step optical authentication system: the micropattern itself, and the underlying pixel-by-pixel fluorescence fingerprint of the microchip.”

The researchers created a millimeter-size approximation of the Mona Lisa that contained a unique, embedded fluorescence fingerprint. Applications could include preventing fraud and vouching for the integrity of data and equipment.

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