The Light Side of Communication


Though signal lamps are no longer a go-to form for relaying messages, modern communication still relies heavily on sending messages with pulses of light. In fact, as optoelectronic technology gets smaller, fiber-optic cables may increasingly connect even the relatively-close components inside a laptop or smart phone.

Associate professor of electrical engineering, physics, and applied physics Hong Tang and electrical engineering postdoctoral fellow Menno Poot are leapfrogging over such a development. Eliminating at least one source of fiber-optic cable entirely, their latest device places the optics directly onto a silicon chip, a process that reduces coupling losses, enhances the device stability, and makes the entire system easily scalable. Their research was published in Applied Physics Letters.

On-chip phase shifting optics, with results

The information in Tang and Poot’s device is encoded in optical signals by modifying the phase of the light field. One way to do this is to use a small heater on the chip, a method that creates decent results but that becomes too hot to effectively implement at the cryogenic temperatures required for superconducting detectors. A second way is to use electro-optical circuits, a method that achieves significantly faster results than the photothermal method and uses less power, but the tradeoff is a lower control range for the resulting chip.

Tang and Poot instead pursued a third methodology, electromechanical phase shifting. “Our method doesn’t require as much power and heat as the photothermal method, and it’s also faster,” says Tang. “And compared to the electro-optical effect, the electromechanical method sacrifices a small amount of speed in favor of a smaller footprint and a larger tunable range.” The phase shifting is accomplished using nanoelectromechanical controlled waveguides. By varying the separation between the waveguides, Tang and Poot’s device changes the effective refractive index of the waveguide and can induce a controlled phase shift in the propagating light signal.

The next step for the team’s research is to see further integration of components and chip, with the ultimate end goal to create a quantum circuit.