Science and Technology Daily, Beijing, December 13th (Reporter Chengkuan Lu) - Nanophotonics technology based on polaritons can manipulate photons at deep sub wavelength scales, which is the key to achieving high-speed optical information processing in the future. Researchers from the National Center for Nanoscience and Technology and other institutions have successfully taken a photo of a low symmetric polariton and achieved real space imaging of the low symmetric phonon polariton, confirming the near-field "axial dispersion" effect and revealing a new feasible path for photon manipulation at the nanoscale. The related research results were published online on December 12th in the journal Nature Nanotechnology.

　　Surface phonon polaritons are a special electromagnetic mode that exists at the interface of polar crystals, and can also be considered as quasi particles formed by the coupling of photons and matter. "It can achieve efficient light field compression and energy focusing, regulate the direction of nanoscale light transmission, and has broad application prospects in nanophotonics, especially in the field of two-dimensional light field control." Qing Dai, co-author of the paper and researcher at the National Center for Nanoscience and Technology, introduced.

　　"However, previously reported phonon excitons exist on the surface of highly symmetric crystals, and their regulatory degrees of freedom are constrained by crystal symmetry, which limits their excellent performance." Qing Dai introduced.

　　Using near-field optical microscopy, Qing Dai's research group and collaborators studied the phonon polaritons of monoclinic crystal cadmium tungstate, and successfully imaged the real space of the surface phonon polariton wavefront of cadmium tungstate crystal, directly confirming the existence of near-field "axial dispersion" effect in low symmetry crystals.

　　"The monoclinic crystal cadmium tungstate has low symmetry, and we observed the optical mode of phonon polaritons on the surface of chromium tungstate crystals using a near-field microscope," said Debo Hu, co first author of the paper and associate researcher at the National Center for Nanoscience and Technology. This is similar to taking a photo of a water wave excited by a stone, but the water wave is not only not circular but also asymmetric in all directions.

　　Regarding this, Qing Dai stated that this study not only provides the most crucial evidence for the near-field "axial dispersion" effect, but also expands the research system of polaritons and provides new methods for controlling planar optical fields. In addition, the near-field "axial dispersion" effect revealed by it implies that different frequencies of phonon polaritons correspond to different optical axis orientations, which can be used to achieve nanoscale wavelength division multiplexing.

   Sources: 科技日报

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