40x boost in CPU speed paves the way for plasmon-based optical communication
Nano antennas bring revolutionary improvement to CPU speed
Research team led by KU professor publishes results in Nature Communications 
 

▲ From the left, Wonjun Choi (first author), researcher at the IBS Center for Molecular Spectroscopy and Dynamics; Yonghyeon Jo (first author), researcher at the IBS Center for Molecular Spectroscopy and Dynamics; and Wonshik Choi, vice director of the IBS Center for Molecular Spectroscopy and Dynamics (corresponding author)

The speed of information processing in computers can be improved by enhancing the integration rate of the central processing unit (CPU). A higher integration rate leads to an increase in the number of elements that negatively affect performance. A recent study has improved the speed of electronic devices using optical signals, which are a few hundred times faster than electronic signals. For this technology to be commercialized, it is essential to overcome the bottleneck of signal delivery that occurs when converting optical into electronic signals.

The research team led by Wonshik Choi, vice director of the IBS Center for Molecular Spectroscopy and Dynamics, resolved the bottleneck by randomly scattering nano antennas on a thin metal film. This method allows the bandwidth to be 40 times larger than that of existing nano antennas.

* Central Processing Unit (CPU): The CPU acts as the brain of a computer and controls the entire system. It receives data from an input device and sends out results via an output device.

Nano antennas are made by drilling holes with a diameter of 200 nanometers (nm) into a thin metal film. Surface plasmon polaritons (SPPs) are generated when light (optical signals) is illuminated. In past research, SPPs were obtained from a regular array of nano antennas. As a result of the multiple antennas behaving like a single antenna, it was not possible to handle multiple signals at the same time.

* Plasmon refers to quasiparticles generated when free electrons oscillate in metal. When light collides with metal under certain conditions, an electron density wave is generated on the surface, similar to the formation of a ripple when a stone is thrown into a pond. This wave is the plasmon, and it moves quickly at optical frequencies. Plasmon that exists on the surface of metallic nanoparticles is called surface plasmon.

Surface plasmon can gather light in a very small area, and then converts optical signals into electric signals. Plasmonics, the study of plasmons, is being conducted around the world as it is expected to make significant contributions to future developments of ultra high-speed computers and the connection of electronic and optical circuits.

The team solved the aforementioned issue through random scattering of nano antennas. They reduced the interference between nano antennas by inducing multiple scattering of plasmon, thus enabling individual nano antennas to assume independent roles.

When multiple nano antennas are effectively implemented, it is possible to deliver maximum information through multiple-input and multiple-output (MIMO). This minimizes the loss of information that occurs when light, which travels in three dimensions, is converted into electrical signals for a two-dimensional surface.

* MIMO technology is used in antenna systems capable of multiple input and output. The increase in the number of antennas implies an increase in the number of multiple-input channels, which leads to a larger bandwidth for information delivery.

While plasmons increase the amount of multiple signals through scattering, it has been difficult to determine their movement. The team identified generation patterns by analyzing SSPs, and succeeded in adjusting the shape of light for SSP control. 

The team simultaneously sent plasmon signals to six microprocessors [Fig. 1]. Moreover, they successfully delivered optical images to SSPs [Fig. 2].

* A microprocessor is a computer processor that integrates various functions, such as arithmetic and logic units, registers, program counters, command decoders, and control circuits, in a small silicon chip. It analyzes and executes commands stored in the main memory device. It serves as the brain of electronic products such as refrigerators, televisions, and automated equipment.

Wonshik Choi, the vice director of the IBS Center for Molecular Spectroscopy and Dynamics and a professor of physics and Korea University, said, “This study presents a new method of connecting nano-scale microprocessors using ultra high-speed optical communication. We expect this to significantly improve the speed of computers.”

The team’s results were published in the online version of Nature Communications (IF 11.470) on March 6.

[ Description of Figures ]

Fig. 1: Plasman signals are delivered at the same time to six microprocessors. The red dots are combined to form a line. Plasmon signals can be delivered to the desired position when phase-controlled light is illuminated on the thin metal film containing the nano antenna.  

Fig. 2: Reconstruction of a 2D image delivered using plasmon signals. As shown in Fig. 2(a), a far-field illumination containing a flower pattern is delivered to randomly scattered nano antennas. As shown in Fig. 2(b), plasmon signals are measured in the counter-clockwise direction along the white dashed line. Using the pre-measured delivery matrix, the flower image is restored as shown in Fig. 2(c). This shows that optical signals that reach individual nano antennas are accurately delivered through plasmon signals.