Caltech’s New Optical Switch Could Lead to Ultrafast Signal Processing

One of the most essential parts of computers, a switch, has been created by engineers at the California Institute of Technology (Caltech) utilizing optical, rather than electrical, components. The pursuit of ultrafast all-optical signal processing and computing may benefit from this advancement.

Optical devices can send signals far more quickly than electrical devices because they work with light pulses rather than electrical signals. To transfer data, newer gadgets frequently use optics for this reason. For instance, compared to traditional Ethernet cables, fiber optic cables offer substantially quicker internet rates.

The area of optics has the potential to transform computers by performing more, quicker, and with less power. However, one of the main drawbacks of today's optics-based systems is that, at some point, transistors based on electronics are still required for effective data processing.

An all-optical switch has now been developed by a team of engineers under the direction of Alireza Marandi, assistant professor of electrical engineering and applied physics at Caltech (more on that later). A switch like that could ultimately allow photonic data processing. On July 28, the study was published in the journal Nature Photonics.

One of a computer's most basic parts is a switch. When a signal enters the switch, the switch either permits the signal to go or stops it depending on specific circumstances. Digital transistors were created to provide this on/off feature, which is the basis for logic gates and binary processing. But until now, using light to perform the same role had been challenging. Contrary to electrons in transistors, which may significantly influence one another's flow and result in "switching," photons often do not interact with one another readily.

The materials Marandi's team utilized and how they employed them were two factors that enabled the breakthrough. They started by picking a crystalline substance called lithium niobate, which is made up of the elements niobium, lithium, and oxygen. Over the past 50 years, this material has shown to be crucial to the area of optics despite not occurring naturally. The material is naturally nonlinear: The optical signals it generates as outputs are not proportionate to the input signals because of the unique way the atoms are organized in the crystal.

While lithium niobate crystals have been utilized in optics for many years, new developments in nanofabrication methods have allowed Marandi and his team to develop integrated photonic devices based on lithium niobate that permit the confinement of light in a small area. The intensity of light increases with space size while using the same amount of electricity. As a result, a higher nonlinear response than would otherwise be conceivable might be produced by the light pulses conveying information through such an optical system.

The light was also spatially constrained by Marandi and his colleagues. They essentially made light pulses shorter and employed a particular design to maintain them that way as they traveled through the apparatus, which gave each pulse a larger peak power.

For a given pulse energy, the combined result of these two strategies—the spatiotemporal confinement of light—significantly increases the degree of nonlinearity, which implies that photons now interact with each other considerably more strongly.

The end result is a nonlinear splitter that can switch in less than 50 femtoseconds by splitting the light pulses into two separate outputs dependent on their energy (a femtosecond is a quadrillionth of a second). Modern electronic switches, in contrast, operate in tens of picoseconds (one picosecond is equal to one trillionth of a second), a difference of several orders of magnitude.