https://www.hpcwire.com/2021/05/04/crystal-ball-gazing-at-nvidia-rd-chief-bill-dally-talks-targets-and-approach/

Conceptually the idea is pretty straightforward.

“This chart (below) shows the general architecture. We start with a laser comb source. This is a laser that produces a number of different colors of light. I say different colors [but they] are imperceptibly different by like 100 gigahertz in frequency, but it produces these different colors of light and sends them over a supply fiber to our transmitter. In the transmitter, we have a number of ring resonators that are able to individually modulate (on-and-off) the different colors of light. So we can take one color of light and modulate it at some bit rate on and off. We do this simultaneously in parallel on all of the other colors and get a bit rate which is a product of the number of colors we have and the bit rate we’re switching per color. We send that over a fiber with a reach of 10-to-100 meters to our receiving integrated circuit. [There] we pick off with ring resonators the different colors that are now either on or off with a bitstream and send that photodetectors and transimpedance amplifiers and on up to the receiver,” described Dally

Dally envisions a future optical DGX where a GPU will communicate via an organic package to an electrical integrated circuit that basically takes that GPU link and modulates the individual ring resonators that you saw in the previous figure on the photonic integrated circuit. The photonic integrated circuit accepts the supply fiber from the laser, has the ring resonator modulators, and drives that fiber to the receiver. The receiver will have an NVSwitch and has the same photonic integrated circuit. But now we’re on the receive side where the ring resonators pick the wavelengths off to the electrical integrated circuit, and it drives the switch.

“The key to this is that optical engine,” he said, “which has a couple of components on it. It has the host electrical interface that receives a short reach electrical interface from the GPU. It has modulator drivers to modulate the ring resonators as well as control circuitry, for example, to maintain the temperature of the ring resonators [which must be at] a very accurate temperature to keep the frequency stable. It then has waveguides to grating couplers that couple that energy into the fiber that goes to the switch