Physicists Unravel the Enigma of Trapped Waves: Shedding Light on 3D Light Localization

With the aid of advanced computing, researchers have successfully unraveled a longstanding mystery surrounding the confinement of light within three-dimensional structures. Their study has demonstrated that random arrangements of metallic spheres can effectively trap or “localize” light, opening up promising avenues for laser technology and photocatalysts. The findings, published in Nature Physics on June 15, mark a significant breakthrough in understanding the behavior of light in three dimensions.

Over the years, scientists have recognized that electrons in materials can either move freely, enabling electrical conduction, or become trapped, behaving as insulators. The occurrence of this phenomenon, known as Anderson localization, hinges on the presence of randomly distributed defects within the material. When physicist Philip W. Anderson introduced this concept in 1958, it revolutionized the field of condensed physics, encompassing both quantum and classical realms, including electrons, acoustic waves, water, and even gravity.

Nevertheless, the mechanics underlying the localization or trapping of electromagnetic waves in three dimensions have remained elusive, despite four decades of extensive research. Led by Professor Hui Cao, a team of researchers has finally provided a definitive answer regarding the potential for light localization in three-dimensional space. This groundbreaking discovery holds tremendous potential for fundamental research and practical applications involving three-dimensionally localized light.

The pursuit of three-dimensional Anderson localization for electromagnetic waves has spanned many decades, punctuated by numerous attempts and disappointments. Although several experimental reports claimed to have achieved 3D light localization, they were met with skepticism due to experimental artifacts or the misattribution of observed phenomena to other physical effects. Consequently, a heated debate ensued, questioning the very existence of Anderson localization for electromagnetic waves in random three-dimensional systems. Since completely eliminating experimental artifacts to obtain conclusive results proved exceedingly challenging, Cao and her colleagues turned to the “indignity of numerical simulation,” as Philip W. Anderson himself described it during his Nobel Prize lecture in 1977. Nonetheless, simulating Anderson localization in three dimensions has long been a formidable computational task.

Cao’s team recently forged a collaboration with Flexcompute, a company that made significant strides in accelerating numerical solutions with their FDTD Software Tidy3D, enabling substantial computational enhancements. This newfound computational power astounded Cao, who remarked, “The Flexcompute numerical solver runs at an astonishing speed. Simulations that we expected would take days can now be completed in just 30 minutes. This allows us to explore numerous random configurations, different system sizes, and various structural parameters to assess the possibility of three-dimensional light localization.”

Cao assembled an international team consisting of her long-term collaborator, Professor Alexey Yamilov from the Missouri University of Science and Technology, Dr. Sergey Skipetrov from the University of Grenoble Alpes in France, Professor Zongfu Yu from the University of Wisconsin, and Dr. Tyler Hughes and Dr. Momchil Minkov from Flexcompute.

By conducting their study free from the artifacts that previously plagued experimental data, they have finally put an end to the long-standing debate surrounding the plausibility of light localization in three dimensions, providing accurate numerical results. First and foremost, they demonstrated the impossibility of localizing light in three-dimensional random aggregates of dielectric materials like glass or silicon, which elucidated the failures of previous experimental efforts spanning several decades. Additionally, they presented unequivocal evidence of Anderson localization for electromagnetic waves within random packings of metallic spheres.

Cao expressed her excitement, saying, “When we observed Anderson localization in the numerical simulation, we were elated. It was truly remarkable, considering the relentless pursuit by the scientific community.”

The significance of their findings extends beyond resolving lingering questions. The research has opened up new possibilities for lasers and photocatalysts. Cao elaborated, “Confining light three-dimensionally in porous metals can amplify optical nonlinearities, optimize light-matter interactions, enable controlled random lasing, and facilitate precise energy deposition. Consequently, we anticipate a multitude of applications arising from these discoveries.”

Reference: “Anderson localization of electromagnetic waves in three dimensions” by Alexey Yamilov, Sergey E. Skipetrov, Tyler W. Hughes, Momchil Minkov, Zongfu Yu and Hui Cao, 15 June 2023, Nature Physics.
DOI: 10.1038/s41567-023-02091-7

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