Research Bits: March 15

Interferometer on chip
Researchers at the University of Rochester developed an optical interferometer on a 2mm by 2mm integrated photonic chip that is capable of amplifying interferometric signals without a corresponding increase in extraneous noise.

Interferometers merge two or more sources of light to create interference patterns that provide information able what they illuminate. “If you want to measure something with very high precision, you almost always use an optical interferometer, because light makes for a very precise ruler,” said Jaime Cardenas, assistant professor of optics at the University of Rochester.

To make the chip, the team applied weak value amplification. “Basically, you can think of the weak value amplification technique as giving you amplification for free. It’s not exactly free since you sacrifice power, but it’s almost for free, because you can amplify the signal without adding noise—which is a very big deal,” Cardenas said.

Weak value amplification is based on the quantum mechanics of light, and basically involves directing only certain photons that contain the information needed, to a detector. The concept has been demonstrated before, “but it’s always with a large setup in a lab with a table, a bunch of mirrors and laser systems, all very painstakingly and carefully aligned,” Cardenas continued.

“Meiting [Song, a PhD student at Rochester] distilled all of this and put it into a photonic chip,” Cardenas says. “And by having the interferometer on a chip, you can put it on a rocket, or a helicopter, in your phone—wherever you want—and it will never be misaligned.”

A 2 mm by 2 mm integrated photonic chip developed by Jaime Cardenas, assistant professor of optics, and PhD student Meiting Song (lead author) will make interferometers—and therefore precision optics—even more powerful. Potential applications include more sensitive devices for measuring tiny flaws on mirrors, or dispersion of pollutants in the atmosphere, and ultimately, quantum applications. (Credit: University of Rochester photo / J. Adam Fenster)

Instead of using a set of tilted mirrors to bend light and create an interference pattern, as in a traditional interferometer, the device includes a waveguide engineered to propagate the wavefront of an optical field through the chip. “This is one of the novelties of the paper,” Cardenas said. “No one has really talked about wavefront engineering on a photonic chip.”

With traditional interferometers, the signal to noise ratio can be increased, resulting in more meaningful input, by simply cranking up the laser power. However, Cardenas noted that the traditional detectors used with interferometers can handle only so much laser power before becoming saturated, at which point the signal to noise ratio can’t be increased. The new device removes that limitation by reaching the same interferometer signal with less light at the detectors, which leaves room to increase the signal to noise ratio by continuing to add laser power. “If the same amount of power reaches the detector in Meiting’s weak value device as in a traditional interferometer, Meiting’s device will always have a better signal to noise ratio,” Cardenas concluded.

The researchers plant to adapt the device for coherent communications and quantum applications using squeezed or entangled photons to enable devices such as quantum gyroscopes.

Cool cables for EV charging
Researchers at Purdue University constructed an EV charging station cable that uses liquid-to-vapor cooling technology to cut the time it takes to charge.

Cooling is an important aspect of EV charging, as higher currents traveling through the cable generate more heat that must be removed for it to remain operational. The researcher’s cable and cooling system can deliver a current 4.6 times that of the fastest available EV chargers on the market today by removing up to 24.22 kilowatts of heat.

Liquid-to-vapor cooling systems capture heat in both liquid and vapor forms, enabling the removal of at least 10 times more heat than pure liquid cooling. This enables a smaller wire diameter inside the charging cable, making it easier to handle.

“The industry has a gap in knowledge and expertise needed to switch from pure liquid cooling to liquid phase change cooling. How do you design the system? What type of equations do you use to optimize it? But we do have this knowledge through our extensive research,” said Issam Mudawar, professor of mechanical engineering at Purdue.

Though the prototype hasn’t been tested on EVs yet, the team demonstrated in the lab that their prototype accommodates a current of over 2,400 amperes, much more than the 1,400-ampere minimum that would be needed to reduce charging times for large commercial EVs to five minutes. The most advanced chargers in the industry currently deliver currents up to 520 amperes, and most chargers available to consumers support currents of less than 150 amperes.

The prototype mimics a real-world charging station, and includes a pump, a tube with the same diameter as an actual charging cable, the same controls and instrumentation, and it has the same flow rates and temperatures.

Charge times will be dependent on the power output ratings of the power supply and charging cable, and on the power input rating of the EV’s battery. To obtain a sub-five minute charge, all three components will need to be rated to 2,500 amperes.

“The industry doesn’t really need EVs to charge faster than five minutes, but we think we can increase the current even more by modifying both the state of the incoming liquid and the design of the cooling space around the conductor wires in the charging cable,” Mudawar said.

The team intends to work with EV or charging cable manufacturers to test the prototype on EVs within the next two years. The testing will determine more details on charge speeds for specific models of EVs.

NFC clothing
Engineers at the University of California Irvine propose an e-textile “body area network” that can enable near-field communication (NFC) at larger ranges.

“If you’ve held your smartphone or charge card close to a reader to pay for a purchase, you have taken advantage of near-field signaling technologies. Our fabrics work on the same principle, but we’ve extended the range significantly,” said Peter Tseng, UCI assistant professor of electrical engineering & computer science. “This means you could potentially keep your phone in your pocket, and just by brushing your body against other textiles or readers, power and information can be transferred to and from your device.”

Amirhossein Hajiaghajani, a UCI Ph.D. student in electrical engineering & computer science, added that the invention enables wearers to digitally interact with nearby electronic devices and make secure payments with a single touch or swipe of a sleeve. “With our fabric, electronics establish signaling as soon as you hover your clothes over a wireless reader, so you can share information with a simple high-five or handshake. You would no longer need to manually unlock your car with a key or separate wireless device, and your body would become the badge to open facility gates.”

Compared to typical NFC, which has a range of a few inches, the researchers extended the signal reach to more than 4 feet using passive magnetic metamaterials based on etched foils of copper and aluminum.

A new high-tech fabric created by engineers at UCI enables wearers to communicate with others, wirelessly charge devices and pass through security gates with the wave of an arm. Credit: Steve Zylius / UCI

Tseng likens the technology to a railway that transmits power and signals as it crisscrosses a garment. Because it works on magnetic induction rather than a continuous hard-wired connection, it is highly flexible and tolerant of bodily motion. The system allows new segments to be added readily, and separate pieces of clothing can be paired to “talk” with one another, such as pants that measure leg movements communicating with a heart-rate monitoring shirt.

An application the researchers see as promising is hospital gowns. They also noted that materials involved in the system are low-cost and easy to fabricate and customize, and varying lengths and branches of the metamaterial “rails” can be heat-pressed onto existing clothing.