Future high-performance information devices should meet both the high-speed operation function and the ultra-large-scale integration requirements. Compared with electrons, photons have the advantages of high speed, low energy consumption, high capacity, etc., and are expected to dramatically improve the information processing capability in the future. Therefore, optoelectronic fusion systems are considered to be an important direction for building the next generation of high-efficiency, highly integrated, low-energy information devices. Optoelectronic interconnection (electrical-optical-electrical conversion) is the basis of photoelectric fusion, equivalent to the toll booths of the intersection of two highways of photoelectricity. The existing silicon-based optoelectronic integration scheme has low efficiency (relying on the multiple photoelectric effect), large size (the optical module can not break through the diffraction limit) and other problems, restricting the flow of information between optoelectronic devices. However, photons do not carry charge and light transmission is limited by the optical diffraction limit, compared to electrons that can be easily regulated by electricity, the nanoscale localization and manipulation of photons is not easy.

     China's solid-state physicist Kun Huang academician in 1951 through the famous "Huang equation" predicted the formation of photons and matter quasiparticles - polarization excitations. After years of research and deeper discovery, polarized excitations have been proven to easily break through the optical diffraction limit, compressing the light wavelength to the nanometer scale, and their field distribution is closely related to the dielectric environment.

    Qing Dai's research team at the National Center for Nanoscience (NCN) has proposed a new idea of using polarized excitons as a medium for optoelectronic interconnection, giving full play to their advantages of high compression and easy regulation of light. Constructing a light-polarized exciton-electric conversion path is equivalent to transforming a highway toll station into an overpass, which has significant advantages: first, high efficiency, the efficiency of light/electric excitation of material surface waves has a huge potential to improve compared to the photoelectric effect; second, high integration, light waves into material surface waves can be converted into a wavelength compression of hundreds of times to easily break through the diffraction limit, which significantly improves the integration of the optical module; third, the arithmetic is strong, the surface waves of materials with photonic properties can be efficiently parallelized, and the material surface waves can be converted into light waves. With the photonic nature of the material surface waves can be efficient parallel computing, thus expanding the existing photoelectric fusion of "optical transmission, electrical computing" into "optical transmission, electrical computing + optical computing", to achieve "1 + 1 > 2 The effect of "1+1>2" is realized.

      In recent research, Qing Dai's group and his collaborators have discovered the "axial dispersion" effect of polarized excitons in low-symmetry crystals (Nat. Nanotech. 2023, 18, 64), solved the problem of long-range transport of graphene equipartitioned excitons (Nat. Commun. 2022, 13: 1465), and proposed a method for heterogeneous excitons (Nat. Commun. 2022, 13: 1465). ), and proposed a new mechanism for heterojunction modulation of polarized excitons (Nat. Nanotech. 2022, 17, 940).

     On this basis, the research team designed and constructed a micro- and nanoscale graphene/molybdenum oxide van der Waals heterojunction, which fully exploits the nanophotonics properties of the different materials, in which the thickness of the atomic layer provides the basis for highly compressed optical modes, the van der Waals stacking satisfies the near-field matching of the mode hybridization, and the linear energy-band structure provides the platform for the modulation of the electric gate voltage. The "phototransistor" function, in which one polarized exciton is used to modulate the switching of another polarized exciton, is thus realized. It is shown that the transistor can realize the dynamic modulation of positive and negative refraction of light, which provides a basis for the construction of optical logic units such as and non-gates. This research is geared toward the significant need for efficient and compact photoelectric interconnections for large-scale integration of optoelectronic fusion devices, and scientifically provides new ideas for solving the difficult problem of breaking through the diffraction limit for efficient photoelectric modulation.

     On February 10, the related research results were published online in Science under the title of Gate-tunable negative refraction of mid-infrared polaritons. National Center for Nanoscience (NCNS) researcher Qing Dai, Professor Javier Abajo of the Institute of Photonic Sciences (IPPS) in Spain were the co-corresponding authors of the article, Associate Researcher Hai Hu of NCNS was the co-first author and one of the co-corresponding authors, and doctoral students Na Chen and Hanchao Teng were the co-first authors. The above research work was supported by the National Key Research and Development Program of China (NKRDP) and the National Natural Science Foundation of China (NSFC).

Link to paper. 

https://www.science.org/doi/10.1126/science.adf1251

Media Coverage:

Science Journal Highlight（https://www.science.org/doi/10.1126/science.adh0386）

Chinese Academy of Sciences（https://www.cas.cn/syky/202302/t20230210_4874522.shtml）

CCTV News（https://content-static.cctvnews.cctv.com/snow-book/index.html?item_id=349057996908596017&toc_style_id=feeds_default&share_to=wechat&track_id=518c8511-bee7-4f9b-abe1-dbca86fe1dce）