Fiber guiding at the Dirac frequency beyond photonic bandgaps

Kang Xie*, Wei Zhang, Allan D. Boardman, Haiming Jiang, Zhijia Hu, Yong Liu, Ming Xie, Qiuping Mao, Lei Hu, Qian Li, Tianyu Yang, Fei Wen, Erlei Wang

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Light trapping within waveguides is a key practice of modern optics, both scientifically and technologically. Photonic crystal fibers traditionally rely on total internal reflection (index-guiding fibers) or a photonic bandgap (photonic-bandgap fibers) to achieve field confinement. Here, we report the discovery of a new light trapping within fibers by the so-called Dirac point of photonic band structures. Our analysis reveals that the Dirac point can establish suppression of radiation losses and consequently a novel guided mode for propagation in photonic crystal fibers. What is known as the Dirac point is a conical singularity of a photonic band structure where wave motion obeys the famous Dirac equation. We find the unexpected phenomenon of wave localization at this point beyond photonic bandgaps. This guiding relies on the Dirac point rather than total internal reflection or photonic bandgaps, thus providing a sort of advancement in conceptual understanding over the traditional fiber guiding. The result presented here demonstrates the discovery of a new type of photonic crystal fibers, with unique characteristics that could lead to new applications in fiber sensors and lasers. The Dirac equation is a special symbol of relativistic quantum mechanics. Because of the similarity between band structures of a solid and a photonic crystal, the discovery of the Dirac-point-induced wave trapping in photonic crystals could provide novel insights into many relativistic quantum effects of the transport phenomena of photons, phonons, and electrons.

Original languageEnglish
Article numbere304
JournalLight: Science and Applications
Issue number6
Publication statusPublished - 19 Jun 2015

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  • Band structure
  • Dirac equation
  • Optical fiber
  • Optical mode
  • Photonic crystal


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