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Light it up: Reimagining the optical diode effect

January 18, 2024
Osaka Metropolitan University
A research group has discovered significant nonreciprocal optical absorption of LiNiPO4, referred to as the optical diode effect, in which divalent nickel (Ni2+) ions are responsible for magnetism, by passing light at shortwave infrared wavelengths used in optical communications. Furthermore, they have uncovered that it is possible to switch the optical diode effect by applying a magnetic field. This is a step forward in the development of an innovative optical isolator that is more compact and can control light propagation, replacing the conventional optical isolators with complex structures.

At the heart of global internet connectivity, optical communications 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.

A team of researchers led by Associate Professor 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 (Ni2+) 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 Professor 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."

Their findings were published in Physical Review Letters.

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Materials provided by Osaka Metropolitan University. Note: Content may be edited for style and length.

Journal Reference:

  1. Kenta Kimura, Tsuyoshi Kimura. Nonvolatile Switching of Large Nonreciprocal Optical Absorption at Shortwave Infrared Wavelengths. Physical Review Letters, 2024; 132 (3) DOI: 10.1103/PhysRevLett.132.036901

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Osaka Metropolitan University. "Light it up: Reimagining the optical diode effect." ScienceDaily. ScienceDaily, 18 January 2024. <>.
Osaka Metropolitan University. (2024, January 18). Light it up: Reimagining the optical diode effect. ScienceDaily. Retrieved March 4, 2024 from
Osaka Metropolitan University. "Light it up: Reimagining the optical diode effect." ScienceDaily. (accessed March 4, 2024).

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