Pure photonic CPUs: a future without electronics?

By using all-optical logic, memory, and multiplexing, Akhetonics is harnessing THz-frequency light on-chip, bypassing electronic speed limits and creating photonic processors that can advance AI inference, networking, and cryptography.

By Michael Kissner, CEO, Akhetonics

“What is the difference between electronic computing and photonic computing?” This is a question that we at Akhetonics often get asked. The quick answer is that one uses electrical signals and the other optical. Yet under the hood, both are just electromagnetic (EM) wave processors. At first glance, an electronic chip and a PIC even look alike, until you inspect them under a microscope and notice that photonic waveguides are much larger.

The difference really comes down to frequency. At low frequencies (Hz to MHz), the EM wave’s wavelength is enormous compared to chip features, so it makes sense to think of electrons shuttling through transistors instead of focusing on the wave. But once you move to the GHz domain, the wavelength is on the order of a millimetre – still much larger than most components, but it no longer covers the entire circuit in a single oscillation. Radio-frequency engineers must therefore think about guiding the wave as well, even if only in a fairly simple way.

When we increase the signal’s frequency by another factor of 1000, we reach the hundreds of THz, and it is all about the EM wave travelling through the system. The wavelength, now around a micrometre, has the same order of magnitude as the components needed to guide and process it on a chip. And this is precisely when we start calling it photonic – instead of electronic – processing.

In short: electronic integrated circuits cram billions of tiny transistors running at GHz speeds with long wavelengths. PICs have fewer components – tens of thousands – but operate at much higher frequencies and shorter wavelengths, allowing for blazing signal rates. It therefore makes sense that any THz CPU would need to be photonic in nature – and this is exactly what Akhetonics does.