Reimagining the optical diode effect
22.03.2024 - New material shows a large nonreciprocal absorption of light depending on the direction of light propagation.
At the heart of global internet connectivity, form an indispensable foundation. Key to this foundation are optical isolators, created by combining multiple components. The result is a complex structure that transmits light in only one direction, to prevent damage to lasers and minimize noise by avoiding the reversal of light. However, some magnetic materials have an optical diode effect – an unconventional nonreciprocal absorption of light manifested by the material itself. This effect leads to a change in transmittance depending on the direction in which the light travels. If this phenomenon can be enhanced, it is expected that optical isolators can be made more compact and efficient.
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Illustration of the optical diode: The arrows indicate the direction in which the light travels, and the size of the cylinder indicates the intensity of the light. The intensity of light transmitted through a magnetic material changes when the direction of light travel is reversed. (Source: Osaka Met. U)
A team of researchers led by Kenta Kimura of the Graduate School of Engineering at Osaka Metropolitan University investigated the phenomenon of nonreciprocal optical absorption in the magnetoelectric antiferromagnet LiNiPO4 at shortwave infrared wavelengths. Their results showed that the absorption coefficient differs by a factor of two or more when the direction of light propagation is reversed. This large nonreciprocal absorption is attributed to the magnetic properties of the divalent nickel ions. Furthermore, the researchers have shown that it is possible to switch the optical diode effect with an applied magnetic field in a non-volatile manner.
“The optical diode effect is an interesting subject of study because it is such an unconventional phenomenon that is far removed from common sense and has the potential to realize unexpected applications. However, there are still many problems at present, such as the low operating temperatures,” explained Kenta Kimura. “Nevertheless, this research has demonstrated the usefulness of compounds containing nickel, which has greatly expanded the scope of material selection. Based on this knowledge, we will continue the development of materials exhibiting a higher performance optical diode effect.” (Source: Osaka Met. U.)
Link: Dept. of Materials Science, Osaka Metropolitan University, Osaka, Japan
