2024-05-07 09:30:38
Scientists used electrical pulses to transfer magnetic information associated with electron spin into a polarized light signal. This new technique makes it possible to significantly increase the information encoding frequency and might revolutionize long-distance optical telecommunications.
In addition to being negatively charged elementary particles, electrons have another interesting property called spin. They behave like tiny magnets rotating on themselves, which is why the spin of electrons can be compared to a magnetic moment. And in the same way that a magnet has a north pole and a south pole, the spin is oriented in two different ways, upwards (up) or downwards (down), so that one of the orientations can be assigned to one bit with a value of 0 and the other to a bit with a value of 1. Such a property therefore offers the possibility of storing information in digital devices such as MRAM (Magnetic Random Access Memory) memories found in computers.
To use this property, this type of equipment must be made from ferromagnetic materials, but once the electrons are removed from this storage device, the spin information is quickly lost and therefore cannot be transported. An international team of scientists1, led by the Jean Lamour Institute, used electrical pulses to transfer magnetic information by converting it into a polarized light signal. Their discovery, which was the subject of a publication in the Nature magazine (free access on the site Nature), might revolutionize long-distance optical telecommunications.
Concretely, the technology developed consists of using light-emitting diodes, a few hundred microns in size, which emit light, that is to say an electromagnetic wave (an electronic field associated with an alternating magnetic field), and to manipulate the circular polarization of this light. When these diodes are used as is, this polarization of the light is not controlled and occurs 50% to the left and 50% to the right. The scientists added a ferromagnetic layer to these diodes and then injected electrons through it. Result: when the spin of an electron is injected in the “up” position into the diode layer, the polarized light orients to the left and when the spin is injected in the “down” position, it orients to the right. In this way it is possible to convert a magnetic signal into an optical signal.
A sharp increase in the frequency of information encoding
Until now, to modulate this spin state on the polarization of light, the technique employed consisted of using magnetic fields. Except that they must be generated by powerful electromagnets, therefore very bulky, unwieldy, and the encoding frequency remains relatively slow, of the order of kHz (kilohertz) or MHz (Megahertz). In this research work, scientists used for the first time an electrical pulse, without magnetic fields, to modulate the magnetization of the injector, converting the spin of the electron into an optical signal exhibiting a specific circular polarization thanks to a quantum effect called “spin-orbit coupling”. Thanks to this effect, the encoding frequency will be able to increase from 10 to 100 GHz (gigahertz) and the experimental device generating these pulses will have a reduced size which makes its implementation much easier.
“The concept of spin-LEDs was initially proposed at the end of the last century, declares Yuan Lu, CNRS researcher at the Jean Lamour Institute of the University of Lorraine. However, to move to practical application, it must meet three crucial criteria: operation at room temperature, absence of magnetic field and electrical control capability. After more than 15 years of dedicated work in this field, our collaborative team has successfully overcome all obstacles. We are very excited to push this technology toward another important spintronic application beyond the magnetoresistance effect.”
In the future, through its implementation in semiconductor laser diodes, called spin lasers, this highly efficient information coding might pave the way for rapid communication over interplanetary distances since the polarization of light can be preserved during space propagation, which would potentially make it the fastest means of communication between Earth and Mars. This new coding might also enable the development of several advanced technologies on earth, such as optical quantum communication and computing, neuromorphic computing for artificial intelligence, ultra-fast and high-efficiency optical transmitters for data centers or applications. Light-Fidelity (LiFi).
1 This research work was carried out in collaboration with the Albert Fert Laboratory (France), the University of Toulouse (France), the Université Paris-Saclay (France), the Ruhr-Universität Bochum (Germany), the Institut of Semiconductors and the Institute of Physics (Chinese Academy of Sciences), National Institute of Advanced Industrial Science and Technology (Japan), University of Minnesota (United States), National Renewable Energy Laboratory (United States) and University at Buffalo (United States).
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