Engineers Demo First Processor that Uses Light for Ultrafast Communications

Estimated reading time: 5 minutes

The researchers came up with a number of key innovations to harness the power of light within the chip.

Each of the key photonic I/O components - such as a ring modulator, photodetector and a vertical grating coupler - serves to control and guide the light waves on the chip, but the design had to conform to the constraints of a process originally thought to be hostile to photonic components. To enable light to move through the chip with minimal loss, for instance, the researchers used the silicon body of the transistor as a waveguide for the light. They did this by using available masks in the fabrication process to manipulate doping, the process used to form different parts of transistors.

After getting the light onto the chip, the researchers needed to find a way to control it so that it can carry bits of data. They designed a silicon ring with p-n doped junction spokes next to the silicon waveguide to enable fast and low-energy modulation of light.

Using the silicon-germanium parts of a modern transistor - an existing part of the semiconductor manufacturing process - to build a photodetector took advantage of germanium's ability to absorb light and convert it into electricity.

A vertical grating coupler that leverages existing poly-silicon and silicon layers in innovative ways was used to connect the chip to the external world, directing the light in the waveguide up and off the chip. The researchers integrated electronic components tightly with these photonic devices to enable stable operation in a hostile chip environment.

The authors emphasized that these adaptations all worked within the parameters of existing microprocessor manufacturing systems, and that it will not be difficult to optimize the components to further improve their chip's performance.

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