Optical engineers at the University of Pennsylvania have created the first computer circuit where logic is performed with light instead of electricity. Dubbed “metatronics,” this light-based logic could enable smaller, faster, and more energy efficient computer chips.

The team, led by Nader Engheta, demonstrated that it’s possible to make resistors, inductors, and capacitors that act on light. By creating a chip that has a comb-like array of nanorods — tiny pillars of silicon nitride (pictured below) — the flow of light can be controlled in such a way that the “voltage” and “current” of the optical signal can be altered. By changing the height and width of the nanorods, and by altering their arrangement, different effects can be achieved. For example, if light has to pass by a short rod and then a tall rod, it might create a resistor-like effect — but a square of four short rods might act as an optical capacitor. The metatronic name comes from the fact that these nanorods are a metamaterial; a material that has has properties that can’t be found in nature.

Because Engheta and co are working with light instead of electricity, their metatronic chip has some very odd properties. For example, light’s polarization — whether the light wave undulates left/right or up/down — affects how it moves through the nanorods. When the light is aligned with the nanorods (pictured above), the circuit fires in parallel; but when light is perpendicular, the circuit is serial. In effect, one set of nanorods can act as two different circuits, which Engheta calls “stereo-circuitry.”

Furthermore, if you rotate the circuit itself through 45 degrees, the light wave would hit the nanorods obliquely, creating a circuit that is neither series or parallel — a setup that doesn’t occur in regular electronics. Eventually — and be careful, this might make your brain explode — you could even build 3D arrays of nanorods, where a single arrangement could act as dozens of different circuits.

To put this into perspective, imagine a low-power, ultra-high-speed CPU that turns into a GPU when you change the input signal — that’s the kind of functionality that metatronic circuits might one day enable. In the short term, though, work needs to be done on optical interconnects– and, as yet, the closest we’ve come to creating an optical transistor is MIT’s optical diode. In the short term it is much more likely that optoelectronic chips — chips that mix electronic logic with optical interconnects, and which can be built using standard semiconductor processes — will be used commercially.

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