New Device Platform Combines Sound And Light For Improved Wireless Communications Performance

Chuck Bednar for redOrbit.com – Your Universe Online
While sound typically travels far slower than light, engineers from the University of Minnesota have created sound that is loud enough so that slower sound waves can bend faster-moving light waves on a computer chip.
This new device platform, which is described in a recent edition of the journal Nature Communications, could improve wireless communications systems using optical fibers, and could also one day be used for computations involving quantum physics.
According to the study authors, sound normally travels 768 miles per hour, while light can reach speeds of in excess of 670,000,000 miles per hour. However, the new National Science Foundation (NSF) and Air Force Office of Scientific Research-funded study creates and confines both types of waves so that the sound can control the light.
The chip used in the experiment was created using a silicon base coated with a layer of aluminum nitride which conducts an electric charge. Applying alternating electrical signals to the material causes it to periodically deform, generating sound waves that grow on its surface similar to how seismic waves generate from an earthquake’s epicenter. This technology has previously been used in cell phones, microwave filters and other wireless devices.
“Our breakthrough is to integrate optical circuits in the same layer of material with acoustic devices in order to attain extreme strong interaction between light and sound waves,” lead author Mo Li, an assistant professor in the Department of Electrical and Computer Engineering, said in a statement.
Li and his colleagues used this cutting-edge type of nanofabrication technology to develop arrays of electrodes that were just 100 nanometers (0.00001 centimeters) wide in order to excite sound waves at an unprecedented high frequency – one higher than 10 GHz, the frequency commonly used for satellite communications.
“What’s remarkable is that at this high frequency, the wavelength of the sound is even shorter than the wavelength of light. This is achieved for the first time on a chip,” said Semere Tadesse, a graduate student in the University of Minnesota’s School of Physics and Astronomy and first author of the study. “In this unprecedented regime, sound can interact with light most efficiently to achieve high-speed modulation.”
“In addition to applications in communications, researchers are pursuing quantum physics applications for the novel device,” the university added. “They are investigating the interaction between single photons (the fundamental quantum unit of light) and single phonons (the fundamental quantum unit of sound). The researchers plan to use sound waves as the information carriers for quantum computing.”
The device was fabricated in the cleanroom at the Minnesota Nano Center at the University of Minnesota. The project was conceived and supervised by Li, while the experiments were designed and the paper co-authored by both he and Tadesse. Tadesse also performed the fabrication, and measured and analyzed the resulting data.
Back in October 2012, Li was part of a University of Minnesota team which invented a unique microscale optical device capable of dramatically increasing download speeds while also lowering the cost of bandwidth. That device used the force generated by light to rapidly turn a mechanical switch of light on and off, a breakthrough which offered superior performance while also reducing power consumption.
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