Isolators are nonreciprocal or “one-way” devices, analogous to electronic diodes. They protect laser sources from back reflections and are needed for routing light signals around optical networks. Currently, the dominant technology for making such nonreciprocal devices requires materials that alter their optical properties in response to magnetic fields, the researchers said.
In a research published in the Nature Photonics journal, the team explains how they apply the minuscule coupling between sound and light to provide a unique solution that enables nonreciprocal devices with virtually any photonic material.
However, the device’s physical size and the availability of materials are not the only issues, the researchers said.
Laboratory attempts at producing compact magnetic optical isolators have always been plagued by large optical loss. 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 magnet-less approach that is competitive.
Benjamin Sohn, Lead Author
The new device is just 200 by 100 µm in size – about 10,000 times smaller than a centimeter squared – and made of aluminum nitride; a transparent material that conveys 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 seeking ways to raise bandwidth or data capacity of these isolators and are assured that they can overcome this obstacle. Once improved, they visualize transformative applications in photonic communication systems, GPS systems, gyroscopes, 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.”
Apart from the technological potential, the researchers cannot help but be captivated by the vital science behind this progress.
In everyday life, we don’t see the interactions of light with sound. 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.
Gaurav Bahl, Co-Author
This research was supported by the United States Defense Advanced Research Projects Agency and the Air Force Research Laboratory.