Hybrid photonics expands capabilities

By Hank Hogan for Photonics – The integration of various new materials with and beyond silicon may lead to improvements in data centers, photovoltaic cells, x-ray machines, and displays.

Alone, nothing is perfect. So when various materials in photonics applications work in tandem, a better performing hybrid approach arises, and teamwork prevails. Examples of such hybrid photonics can be found in existing and emerging commercial products. However, to successfully compete with incumbent technologies, hybrids must integrate different materials and simultaneously achieve required performance and reliability.

One place where a hybrid approach is both successful and commercially important is in data centers, said Eric Mounier, an analyst at the Lyon, France-based research firm Yole Développement. Increasingly, the centers use optical transceivers based on hybrid photonics for data communication. Silicon and related oxides or nitrides provide the optical waveguide function, and other semiconductors handle different tasks.

“In the receiver, for example, InP [indium phosphide] or Ge [germanium] is used because of the good performances in photodetection,” Mounier said. “For the transmitter, InP is used for the uncooled laser source because of the lasing capability of this material.”

A silicon base offers the best platform for the integration of electronic and optical components. But because light cannot be generated from silicon, a hybrid material approach is the only possibility for achieving successful and fully functional integration.

InP, a III-V semiconductor, can be incorporated into a silicon photonic chip in various ways. Santa Clara, Calif.-based Intel grows InP on relatively small 2- or 3-in. wafers. The wafer is diced into little pieces and the pieces are integrated at specific spots in silicon photonic chips, which are fabricated on a 300-mm (12-in.) wafer.

When the two materials are brought together, there are benefits, according to Robert Blum, general manager for new business at Intel’s Silicon Photonics Product Division. “In addition to the full suite of passive silicon photonics components, we can integrate indium phosphide photodiodes and active components such as lasers with very different wavelengths,” he said.

This ability to integrate makes it possible to multiplex various lasers and data channels on the same chip. Multiple lasers enable higher data rates because, for example, four 25-Gb/s channels can be combined to create a 100-Gb/s connection. As the speed capability of individual channels increases, the total bandwidth realized by multiplexing can, too.

Blum said electronic and photonic chips may both be built largely out of silicon but with various fabrication technologies. At the same time, there is, of course, an increasing demand for faster data communication rates. One solution is to combine everything — hybrid photonics and electronics — into a single package that puts the photonics as close as possible to the electronics, an approach Intel followed when it created a 12.8-Tb/s (12,800-Gb/s) network switch. He said such approaches to packaging for data communications, as well as for sensing, are a big focus for Intel.

The company is keeping an eye on emerging photonic materials. Integration with silicon could open up a range of new applications in sensing, biotech, and elsewhere, Blum said… Full article