Power/Performance Bits: Oct. 9

Topological insulator waveguides
Engineers at the University of Pennsylvania and Polytechnic University of Milan applied topological insulators to photonic chips to make reconfigurable waveguides.

In topological insulators, charged particles can flow freely on the material’s edges but can’t pass through the interior. For photonics, topological insulators with edges that could be redefined means that the complexity of photonic waveguides available on a given chip could be maximized, saving space.

“This could have a big impact on large-information capacity applications, like 5G, or even 6G, cellphone networks,” said Liang Feng, assistant professor in Penn Engineering’s Departments of Materials Science and Engineering and Electrical and Systems Engineering. “We think this may be the first practical application of topological insulators.”

The researchers’ prototype photonic chip is roughly 250 microns squared, and features a tessellated grid of oval rings. By “pumping” the chip with an external laser, targeted to alter the photonic properties of individual rings, they are able to alter which of those rings constitute the boundaries of a waveguide.

Microscope details of the researchers’ photonic chip. (Source: Penn Engineering / University of Pennsylvania)

By changing the pumping patterns, photons headed in different directions can be routed around each other, allowing photons from multiple data packets to travel through the chip simultaneously.

“We can define the edges such that photons can go from any input port to any output port, or even to multiple outputs at once,” Feng said. “That means the ports-to-footprint ratio is at least two orders of magnitude greater than current state-of-the-art photonic routers and switches.”

“Our system is also robust against unexpected defects,” Han Zhao, a graduate student at Penn, noted. “If one of the rings is damaged by a grain of dust, for example, that damage is just making a new set of edges that we can send photons along.”

The system still requires an off-chip laser source to change the shape of the waveguides, making it not yet feasible for data centers or other commercial applications. However, the team will next tackle creating a fast reconfiguring scheme in an integrated fashion.

Soft tactile logic
Researchers at North Carolina State University and Jiangnan University devised a soft material that can sense and compute without a centralized processor. Called ‘soft tactile logic’ by the researchers, the system can make decisions at the material level, where the sensor receives input.

“Our approach was inspired by octopuses, which have a centralized brain, but also have significant neuronal structures throughout their arms. This raises the possibility that the arms can ‘make decisions’ based on sensory input, without direct instruction from the brain,” said Michael Dickey, a Professor of Chemical and Biomolecular Engineering at North Carolina State University.

The team’s prototypes are comprised of pigments that change color at different temperatures mixed into soft, stretchable silicone. The pigmented silicone contains channels that are filled with metal that is liquid at room temperature to effectively create a squishy wire nervous system.

Pressing or stretching the silicone deforms the liquid metal, which increases its electrical resistance, raising its temperature as current passes through it. The higher temperature triggers color change in the surrounding temperature-sensitive dyes, giving the overall structure a tunable means of sensing touch and strain.

The researchers also developed soft tactile logic prototypes in which deforming the liquid metal by touch redistributes electrical energy to other parts of the network, causing material to change colors, activating motors or turning on lights. Touching the silicone in one spot creates a different response than touching in two spots; in this way, the system carries out simple logic in response to touch.

“This is a proof of concept that demonstrates a new way of thinking about how we can engineer decision-making into soft materials,” Dickey said. “There are living organisms that can make decisions without relying on a rigid centralized processor. Mimicking that paradigm, we’ve shown materials-based, distributed logic using entirely soft materials.”

The researchers are currently exploring ways to make more complex soft circuits, inspired by the sophisticated sensors and actuators found in biological systems.

Graphene health monitors
Researchers at ICFO demonstrated three different health monitoring devices that utilize graphene and quantum dots for non-invasive optical-based sensors that can measure a broad set of vital signs. The devices are conformable to skin and can provide continuous measurement of heart rate, respiration rate and blood pulse oxygenation, as well as exposure to UV radiation from the sun.

Data from the devices is visualized and stored on a mobile phone interface connected to the wearable via Bluetooth. In addition, the device can operate battery-free, since it is charged wirelessly through the phone.

“The booming wearables industry is eagerly looking to increase fidelity and functionality of its offerings. Our graphene-based technology platform answers this challenge with a unique proposition: a scalable, low-power system capable of measuring multiple parameters while allowing the translation of new form factors into products,” said Antonios Oikonomou, business developer at ICFO.

“It was very important for us to demonstrate the wide range of potential applications for our advanced light sensing technology through the creation of various prototypes, including the flexible and transparent bracelet, the health patch integrated on a mobile phone and the UV monitoring patch for sun exposure. They have shown to be versatile and efficient due to these unique features”, said Emre Ozan Polat of ICFO.

The first device, a flexible and transparent wristband that adapts to the skin surface and provides continuous measurement during activity, incorporates a flexible light sensor that can optically record the change in volume of blood vessels due to the cardiac cycle, and then extract different vital signs such as heart rate, respiration rate and blood pulse oxygenation.

The second device, rather than being a wearable, is a graphene patch that can be placed on a mobile phone screen. When a user places a finger on the screen, the patch measures and displays vital signs in real time. The device uses ambient light to operate, resulting in low power consumption.

The third device is a UV patch capable of wirelessly transferring both power and data, and operating battery-free to sense the environmental UV-index. The patch operates with a low power consumption and has a highly efficient UV detection system that can be attached to clothing or skin, and used for monitoring radiation intake from the sun, alerting the wearer of any possible over-exposure.

“We are excited about the prospects for this technology, pointing to a scalable route for the integration of graphene-quantum-dots into fully flexible wearable circuits to enhance form, feel, durability, and performance.” said Prof. Frank Koppens, leader of the Quantum Nano-Optoelectronics group at ICFO. “Such results show that this flexible wearable platform is compatible with scalable fabrication processes, proving mass-production of low-cost devices is within reach in the near future.”