How will the calculations be done in a light processor?

informatics

Technological Innovation Website Editor – 10/07/2022

computer technologies

Ecosystem of light computing technologies.
[Imagem: Shuming Jiao et al. – 10.29026/oes.2022.220010]

light processors

Whether you’re reading this story on your cell phone or on your computer, your device’s processor is running at full speed. a small chip containing billions of basic components called transistors, mounted in structures called logic gates.

And the fact that we expect our next device to be faster doesn’t come by chance: It really needs to be to meet the demands of new applications and new features.

But this is becoming more and more difficult because it is not possible to indefinitely increase the number of transistors on each chip, not to mention that they heat up more and more and consume the battery more and more quickly.

One of the alternatives for this is to replace the electricity that makes the transistors work with light: There is nothing faster than light and computing with photons practically does not release heat, in addition to drastically reducing energy consumption.

Furthermore, a light field has amplitude, phase, time, space, frequency, polarization, and other dimensions, which can be used to represent information, while reflection, refraction, interference, diffraction, and other optical effects can be used to process information. So it seems natural to use light for computing.

That is, optical computers, with their processors that use light instead of electricity, are definitely an option to consider, replacing electronic devices with photonic devices, and electrical signals with optical signals.

To see where we are on this path, Shuming Jiao and his colleagues at the University of Science and Technology of Southern China have reviewed the entire field of research, and have shown the most advanced in the true zoo of options presented so far.

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Simple logic gates assembled with nanowires (input marked in red and output marked in blue).
[Imagem: Shuming Jiao et al. – 10.29026/oes.2022.220010]

optical logic ports

The challenge to make these optical processors viable is to build logic gates that do the calculations with light. One of the most promising avenues is in an optical component called an optical semiconductor amplifier (AOS), which resembles an optical version of the electronic transistor.

An AOS allows you to obtain a variety of non-linear effects between input and output light signals of different frequencies, which can be used to build mathematical relationships typical of logic gates, such as AND, OR, XOR, etc. In addition, AOS has the effect of four-wave mixing: Through appropriate settings, two light signals of different frequencies can be used as input to generate a third light frequency as an output, and the phase of the output signal is the sum. of the phases of the two input signals.

Highly non-linear optical fibers (HNLF) represent another option. It is another type of optical component that has many properties similar to AOS and can also be used in the assembly of optical logic gates.

computer technologies

Schematics of logic gates in semiconductor optical amplifiers (top) and photonic crystals (bottom).
[Imagem: Shuming Jiao et al. – 10.29026/oes.2022.220010]

waveguides

More recently, with the development of integrated photonics and manufacturing technology at micro and nano scales, it has become possible to build waveguides and other components in an integrated way inside optical chips, allowing the construction of the first miniaturized versions of optical logic gates. – remember that the wavelength of light is huge compared to the size of most modern transistors, something around two orders of magnitude.

In the waveguide, it is easier to adjust the phase, since the light propagation length can be changed. The light intensity after the interference of these two light waves can be used as the output of a logic gate: Depending on the difference in amplitude and phase of the input signal, the light intensity after a constructive or destructive interference can be equivalent to the value output of the logic gate, something comparable to traditional 0s and 1s.

computer technologies

Hybrid implementation with linear and micro-ring waveguides.
[Imagem: Shuming Jiao et al. – 10.29026/oes.2022.220010]

Ring Micro-Resonators

A derived strand combines linear waveguides with ring-shaped micro waveguides, or ring microresonators, which are mounted in a system in which light waves can be propagated through multiple coupling resonances, such as multiple mechanical gears, to achieve a type of logic port operation.

And there are also more “exotic” options, with optical logic gates being assembled using surface plasmons, nanowires, photonic crystals, lithium niobate-based optoacoustic components, etc.

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open future

As with quantum computing, we still don’t know which of these platforms will finally make optical or photonic computers viable.

Shuming Jiao and his colleagues concluded that we are still a long way from designing and building a qualified optical logic gate for practical applications.

In fact, getting the appropriate logic outputs is just a first step. Then it will be necessary to make a series of them work together, make circuits with error correction, etc.

“To truly achieve an ‘Excellent’ score, optical logic gates need to outperform electronic logic gates, showing obvious advantages such as faster calculation speed and lower power consumption. many challenges. Most existing optical logic ports cannot meet all requirements,” the team wrote.

And one cannot escape the eventual need for disruptive innovation either: “Of course, photons and electrons are inherently different, and it is also open to debate whether the ‘bottom-up’ computer structure of the electronic world, built from the single logic gates, still applicable in the photonic world. Optical logic gate research still has a lot of room for further exploration and development in the future,” concluded Shuming Jiao and his colleagues.

Bibliography:

Article: All-optical logic gate computing for high-speed parallel information processing
Authors: Shuming Jiao, Junwei Liu, Liwen Zhang, Feihong Yu, Guomeng Zuo, Jingming Zhang, Fang Zhao, Weihao Lin, Liyang Shao
Magazine: Opto-Electronic Science
DOI: 10.29026/oes.2022.220010

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