Science

All-optical switch device paves the way for faster fiber optic communications

Schematic diagram of an optical cavity with a one-molecule-thick layer of tungsten diselenide (WSe2) at the antinode, which is the point of maximum optical field intensity. Credit: Deng Lab, University of Michigan

Modern high-speed internet uses light to quickly and reliably transmit large amounts of data through fiber optic cables, but currently optical signals become a bottleneck when data processing is required. To do so, it must be converted into an electrical signal for processing before being sent further.

Devices called all-optical switches can use light to control other optical signals without the need for electrical conversion, saving both time and energy in fiber-optic communications.

A University of Michigan-led research team has demonstrated an ultrafast all-optical switch by pulsing spirally twisted circularly polarized light into an optical cavity lined with ultrathin semiconductors. The study was recently published in the journal Nature Communications.

The device can function as a standard optical switch, switching signal beams of the same polarization when a control laser is turned on or off, or as a type of logic gate called an exclusive-OR (XOR) switch. The optical input twists clockwise and the other counterclockwise, but not when both inputs are the same.

“Switches are the most fundamental building blocks of any information processing device, so all-optical switches are the first step toward building all kinds of optical computing and optical neural networks,” said UM’s physics doctoral student. said Lingxiao Zhou, student and lead author of the book. the study.

Optical computing has lower losses, which makes it more desirable than electronic computing.

“Extremely low power consumption is the key to the success of optical computing. The research our team has conducted does just that by using unusual two-dimensional materials to switch data at very low energy per bit. We addressed the problem,” said Stephen Forrest, Peter A. Franken Distinguished Award recipient. Professor of Electrical Engineering at UM and contributor to this study.

To accomplish this, the researchers pulsed a helical laser at regular intervals through an optical cavity (a series of mirrors that captures light and moves it back and forth over and over again), increasing the laser’s intensity by two orders of magnitude.

When a one-molecule-thick layer of the semiconductor tungsten diselenide (WSe2) is embedded within an optical cavity, intense oscillating light expands the electronic band of available electrons within the semiconductor. This is a nonlinear optical effect known as the optical Stark effect. . This means that when an electron jumps to a higher orbit, it absorbs more energy, and when it jumps down, it releases more energy. This is known as a blue shift. This changes the fluence of the signal light, or the amount of energy delivered or reflected per unit area.

In addition to modulating the signal light, the optical Stark effect generates a pseudomagnetic field that affects electronic bands in the same way as magnetic fields. Its effective strength was 210 Tesla, much more powerful than Earth’s strongest magnet, which is 100 Tesla. This extremely strong force, felt only by electrons whose spins match the helicity of light, temporarily splits bands of electrons with different spin orientations and directs all electrons in the aligned bands toward the same orientation.

By changing the direction in which the light is twisted, the researchers were able to change the order of electronic bands with different spins.

The short uniform spin directionality of electrons in different bands also breaks what is called time reversal symmetry. Essentially, time-reversal symmetry means that the underlying physics of the process is the same before and after, implying conservation of energy.

This cannot normally be observed in the macroscopic world because of the way energy is dissipated by forces such as friction, but if you can take a video of a spinning electron, you can play it back or forward. Also, electrons obey the laws of physics. When it rotates in one direction, it turns into an electron that rotates in the opposite direction with the same energy. However, the time reversal symmetry is broken in a pseudomagnetic field. Because when unwound, electrons spinning in opposite directions have different energies, and the energies of different spins can be controlled by the laser.

“Our results have many new implications, both in basic science, where control of time-reversal symmetry is a requirement for creating exotic states of matter, and in technology, where the exploitation of such huge magnetic fields becomes possible. It opens the door to possibilities,” said Hui Deng. Professor of Physics and Electrical and Computer Engineering at UM and corresponding author of the study.

More information: Lingxiao Zhou et al., Cavity Floquet Engineering, Nature Communications (2024). DOI: 10.1038/s41467-024-52014-0

Provided by University of Michigan School of Engineering

Source: All-optical switch device paves the way for faster fiber optic communications (October 19, 2024) from https://phys.org/news/2024-10-optical-device-paves-faster-fiber 2024 Retrieved October 19, 2016. html

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