Illinois researchers have demonstrated that sound waves can be used to produce ultraminiature optical diodes that are tiny enough to fit onto a computer chip. These devices, called optical isolators, may help solve major data capacity and system size challenges for photonic integrated circuits, the light-based equivalent of electronic circuits, which are used for computing and communications.

Isolators are nonreciprocal or “one-way” devices similar to electronic diodes. They protect laser sources from back reflections and are necessary for routing light signals around optical networks. Today, the dominant technology for producing such nonreciprocal devices requires materials that change their optical properties in response to magnetic fields, the researchers said.

“There are several problems with using magnetically responsive materials to achieve the one-way flow of light in a photonic chip,” said mechanical science and engineering professor and co-author of the study Gaurav Bahl. “First, industry simply does not have good capability to place compact magnets on a chip. But more importantly, the necessary materials are not yet available in photonics foundries. That is why industry desperately needs a better approach that uses only conventional materials and avoids magnetic fields altogether.”

In a study published in the journal Nature Photonics, the researchers explain how they use the minuscule coupling between light and sound to provide a unique solution that enables nonreciprocal devices with nearly any photonic material.

However, the physical size of the device and the availability of materials are not the only problems with the current state of the art, the researchers said.

“Laboratory attempts at producing compact magnetic optical isolators have always been plagued by large optical loss,” said graduate student and lead author Benjamin Sohn. “The photonics industry cannot afford this material-related loss and also needs a solution that provides enough bandwidth to be comparable to the traditional magnetic technique. Until now, there has been no magnetless approach that is competitive.”

The new device is only 200 by 100 microns in size – about 10,000 times smaller than a centimeter squared – and made of aluminum nitride, a transparent material that transmits light and is compatible with photonics foundries. “Sound waves are produced in a way similar to a piezoelectric speaker, using tiny electrodes written directly onto the aluminum nitride with an electron beam. It is these sound waves that compel light within the device to travel only in one direction. This is the first time that a magnetless isolator has surpassed gigahertz bandwidth,” Sohn said.

The researchers are looking for ways to increase bandwidth or data capacity of these isolators and are confident that they can overcome this hurdle. Once perfected, they envision transformative applications in photonic communication systems, gyroscopes, GPS systems, atomic timekeeping and data centers.

“Data centers handle enormous amounts of internet data traffic and consume large amounts of power for networking and for keeping the servers cool,” Bahl said. “Light-based communication is desirable because it produces much less heat, meaning that much less energy can be spent on server cooling while transmitting a lot more data per second.”

Aside from the technological potential, the researchers can’t help but be mesmerized by the fundamental science behind this advancement.

“In everyday life, we don’t see the interactions of light with sound,” Bahl said. “Light can pass through a transparent pane of glass without doing anything strange. Our field of research has found that light and sound do, in fact, interact in a very subtle way. If you apply the right engineering principles, you can shake a transparent material in just the right way to enhance these effects and solve this major scientific challenge. It seems almost magical.”

STMicroelectronics (NYSE:STM) and USound, a fast-growing audio company, have delivered the first silicon micro-speakers resulting from their technology collaboration announced last year. Engineering samples are now with lead customers, and trade demonstrations will take place during CES 2018, in Las Vegas.

These extremely small speakers, expected to be the thinnest in the world and less than half the weight of conventional speakers, enable wearable tech such as earphones, over-the-ear headphones, or Augmented-Reality/Virtual-Reality (AR/VR) headgear to become even more compact and comfortable. Their extremely low power consumption saves extra weight and size by allowing smaller batteries, and unlike conventional speakers they generate negligible heat.

As MEMS (Micro Electro-Mechanical Systems) devices, the speakers are leveraging technology that has already revolutionized the capabilities of smartphones and wearables. High-performing MEMS motion sensors, pressure sensors, and microphones built on silicon chips are the critical enablers for context sensing, navigation, tracking, and other features that mobile users now rely on every day. With MEMS advancements now coming to speakers, designers can further miniaturize the audio subsystem, reduce power consumption, and create innovative features like 3D sound. MEMS-industry analyst Yole Développement values the overall micro-speakers market at $8.7 billion^[1] currently, and expects MEMS manufacturers to capture share with silicon-based devices.

“This successful project combines USound’s design flair and ST’s extensive investment in MEMS expertise and processes, including our advanced thin-film piezo technology PeTra (Piezo-electric Transducer),” said Anton Hofmeister, Vice President and GM of MEMS Microactuators Division, STMicroelectronics. “Together, we are winning the race to commercialize MEMS micro-speakers by delivering a more highly miniaturized, efficient, and better-performing solution leveraging the advantages of piezo-actuation.”

“ST has provided the production expertise and manufacturing muscle to realize our original concept as a pace-setting, advanced product ready for consumer-market opportunities,” said Ferruccio Bottoni, CEO of USound. “These tiny speakers are now poised to change the design of audio and hearable products, and open up new opportunities to develop creative audio functionalities.”

In addition to applications in mobiles, audio accessories, and wearables, the new piezo-actuated silicon speakers support innovation in a wide variety of hearable electronics, including home digital assistants, media players, and IoT (Internet-of-Things) devices.

USound will demonstrate prototype AR/VR glasses containing multiple MEMS speakers per side, to invited guests at ST’s private suite during CES 2018. The demo will leverage the speakers’ ultra-thin form factor, low weight, and high sound quality to show how miniaturized audio systems can deliver outstanding experiences, and advanced features such as beam forming for private audio, within the extremely tight size, weight, and power constraints imposed by glasses and other wearables.

Researchers at Aalto University, Finland, have developed a biosensor that enables creating a range of new easy-to-use health tests similar to home pregnancy tests. The plasmonic biosensor can detect diseased exosomes even by the naked eye. Exosomes, important indicators of health conditions, are cell-derived vesicles that are present in blood and urine.

A rapid analysis by biosensors helps recognize inflammatory bowel diseases, cancer and other diseases rapidly and start relevant treatments in time. In addition to using discovery in biomedicine, industry may use advanced applications in energy.

Researchers created a new biosensor by depositing plasmonic metaparticles on a black, physical body that absorbs all incident electromagnetic radiation. A plasmon is a quantum of plasma oscillation. Plasmonic materials have been used for making objects invisible in scientific tests. They efficiently reflect and absorb light. Plasmonic materials are based on the effective polarizabilities of metallic nanostructures.

The carriers containing Ag nanoparticles are covered with various dielectrics of AlN, SiO2 and the composites thereof that are placed on a black background to enhance the reflectivity contrast of various colours at a normal angle of incidence. Credit: Aalto University

“It is extraordinary that we can detect diseased exosomes by the naked eye. The conventional plasmonic biosensors are able to detect analytes solely at a molecular level. So far, the naked-eye detection of biosamples has been either rarely considered or unsuccessful”, says Professor Mady Elbahri from Aalto University.

Plasmonic dipoles are famous for their strong scattering and absorption. Dr. Shahin Homaeigohar and Moheb Abdealziz from Aalto University explain that the research group has succeeded in demonstrating the as-yet unknown specular reflection and the Brewster effect of ultrafine plasmonic dipoles on a black body host.

“We exploited it as the basis of new design rules to differentiate diseased human serum exosomes from healthy ones in a simple manner with no need to any specialized equipment”, says Dr. Abdou Elsharawy from the University of Kiel.

The novel approach enables a simple and cost-effective design of a perfect colored absorber and creation of vivid interference plasmonic colors.

According to Elbahri, there is no need to use of sophisticated fabrication and patterning methods. It enables naked-eye environmental and bulk biodetection of samples with a very minor change of molecular polarizability of even 0.001%.