Team achieves dual-band optical processing

A team led by Vanderbilt engineers has achieved the ability to transmit two different types of optical signals across a single chip at the same time.

The breakthrough heralds a potential dramatic increase in the volume of data a silicon chip can transmit over any period of time. With this work, the research team moved beyond theoretical models and demonstrated dual-band optical processing, a significant advance in silicon photonics.

Using patterned silicon to transmit optical signals uses less power without heating up or degrading the signal. Silicon photonics uses light rather than electrical signals to transmit data. The need for faster and expanded processing has all but outstripped the limits of adding more wire to smaller and smaller chips, which requires more power, creates more heat, and risks data integrity.

Still, doing more with the same chip has been challenging. Silicon waveguides provide the principle building block of on-chip photonics, confining light and routing it to functional optical components for signal processing. Different forms of light need different waveguides, but linear scaling to accommodate more waveguides would quickly surpass the available space of a silicon chip in the standard form factor.

“It has been difficult to combine near-infrared and mid-infrared transmission in the same device,” said Mingze He, a Vanderbilt mechanical engineering PhD student and first author of the paper. “Guided Mid-IR and Near-IR Light within a Hybrid Hyperbolic-Material/ Silicon Waveguide Heterostructure,” was published online and in print in Advanced Materials.

Joshua Caldwell, associate professor of mechanical engineering, and Cornelius Vanderbilt Professor Sharon Weiss, professor of electrical engineering, led the team.

Two innovations—a novel approach and device geometry—allowed disparate frequencies of light to be guided within the same structure. Such frequency multiplexing is not new but the ability to expand the bandwidth within the same available space is.

Leveraging the infrared properties of hexagonal boron nitride, researchers devised a hybrid, hyperbolic-silicon photonic waveguide platform.

The structure was demonstrated to guide long, mid-infrared wavelengths within nanoscale thick- ness slabs, with the optical modes following the path of the underlying silicon waveguide.

A novel approach and device geometry allow the guiding of disparate frequencies of light within the same structure, a significant advance in silicon photonics.

Mid-IR is widely used in the chemical and agricultural industries. Applications of near-IR include telecommunications and medical diagnostics.