Why do computers use electricity instead of light?

Most of us are aware of the fact that light travels quicker than electricity. In fact, in everyday electrical and electronic devices, the signals or energy travel as electromagnetic waves on the order of 50% – 99% of the speed of light, while the electrons themselves move even more slowly. A device such as a computer also draws power even when it’s turned off or in hibernation mode. So that leaves the question: wouldn’t our computers run much faster, and more efficiently, if they used light instead of electricity to operate?

Currently the reasons we use electricity instead of light to operate our computers are several-fold. One of the main reasons is that silicon electronics are cheap, especially when compared to optics, which are expensive for things on the same scale as silicon electronics. And unlike optics, silicon electronics can be made very small, which also makes them easier to use.

With silicon electronics, there’s a deeper understanding of how to make everything work when producing many devices on a single piece of material. On the other hand, optics have proven to be quite tough. Of course optical diodes and optical transistors are available to use through different methods, but not well enough that it’s possible to fabricate billions of them on a single piece of material and have the majority of them work successfully 100% of the time.

Then we have interconnects. On silicon, they’re simple because it’s basically just melting metal. With optics, alignment is difficult, and at best you’ll get about half the power from one side of the connector to the next for dissimilar interfaces.

CMOS, the most typical transistor technology for computers sucks power only when switching. There’s also leakage, but the bulk of power use comes from switching, meaning it sips power in small amounts. Because optics doesn’t have a CMOS equivalent, it would constantly be draining power. Furthermore, most optical switching is achieved through nonlinear optics, which also uses quite a bit of energy.

Both options are fascinating, and each bring about many applications, but because of the points above, it’s unlikely that we’ll be seeing a light-based computer take a seat at the more generic computing table anytime soon.

Source: Forbes