Letting in light

Light anchors the age of information. Light rays pulse through a network of undersea cables tangled across the globe, linking continents and countries, and bringing lightning-fast data onto our devices. The data between two servers are connected and transmitted by optical fibres. While optical fibres take care of what goes on outside the servers, much of what happens within the server is a different story, carried out by electrical signals travelling through copper cables between circuit boards. But as artificial intelligence (AI) drives an explosion of data exchange, copper has struggled to keep up.  

The remedy could be light. The semiconductor industry is realising that to facilitate high-speed data transfer, optical fibres need to replace a majority of electrical connections inside servers. The new role brings light transmission right up to the chip, and makes optical interconnects — the system of data transmission using light — an area of growing interest. 

Rohin Kumar betted on Graphics Processing Units (GPUs) getting better at computing almost five years ago. The bottleneck, he rightly assessed, would be moving high-frequency data. "We foresaw interconnects as the bigger issue because AI applications were no longer a single GPU problem," says Kumar, Co-founder of LightSpeed Photonics, an electronics company based in Hyderabad. A single AI model needs multiple GPUs connected via direct attach copper cables. "The skin effect limits how much high-frequency data can be transferred in a copper cable," he explains. The skin effect refers to the tendency of current to flow near the outer surface of the wire, thereby reducing the effective area of charge transfer.