Friday, April 8, 2022

New spin lasers for ultra-fast data transfer

Martin Hofmann receives funding as part of a Reinhart-Koselleck project for the development of spin lasers.
Credit: RUB, Marquard

The conventional type of Internet data transmission soon reaches fundamental physical limits. The process can only become faster if you rely on a different principle. Bochum researchers do that.

The transfer of data today is based on light pulses that are sent through fiber optic cables. The faster the light intensity varies, the faster you can transfer information. However, fundamental physical limits of the lasers that generate the modulated light prevent the process from becoming much faster than it is currently. The team led by Prof. Dr. Martin Hofmann, chair of photonics and terahertz technology at the Ruhr University Bochum. With the help of spin lasers, the researchers want to encode information in the polarization of light instead of in light intensity. The German Research Foundation will support the work in the future as part of a Reinhart-Koselleck project with 1.25 million euros for five years.

Change the spin instead of moving electrons

Changes in light intensity are brought about by electricity modulation. To do this, many electrons have to be moved, which is not as fast as possible, but with a maximum frequency of around 40 gigahertz. It looks different when you code the information in the polarization of light, more precisely in a polarization oscillation: in linearly polarized light, light waves always vibrate on the same level. If the vibration level rotates, one speaks of circular polarized light. The Bochum researchers created a special form of circular polarized light, the polarization state of which varies extremely quickly.

These polarization oscillations use a quantum mechanical property of the electrons, the spin, and are therefore not subject to the same limitations as the change in light intensity. By specifically influencing the spin of electrons in a laser, the researchers can trigger the oscillation.

Five times faster than standard lasers

The basis for this are so-called vertical cavity surface emitting lasers, which Martin Hofmann and his team would like to examine in more detail as part of the Reinhart-Koselleck project. The researchers inject electrons into these semiconductor lasers. They align their spin in such a way that polarization oscillations arise. Published in a journal Nature in 2019 Work they showed that this principle could potentially achieve modulation frequencies of over 200 gigahertz. "This is more than five times faster than the fastest intensity-modulated standard lasers currently used," says Hofmann.

The aim of the Bochum engineers is to implement components based on vertical cavity surface-emitting lasers that are not only many times faster than conventional technologies, but also significantly more energy efficient than the current standard lasers.

Source/Credit: Ruhr University Bochum | Julia Weiler

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