Xi'an Institute of Optics and Fine Mechanics has made new progress in the field of metasurface nonlinear photonics

Recently, the Research Group of Nonlinear Photonics Technology and Applications in the State Key Laboratory of Transient Optics and Photonics Technology of Xi'an Institute of Optics and Fine Mechanics has made important progress in the field of super surface nonlinear photonics. Relevant research results were published in the internationally famous journal Nanoscale Horizons. The first author of the paper is Zhang Congfu, a 2021 doctoral student.

The mid infrared band (3-5 μ m) plays a crucial role as an atmospheric window in many fields such as biomedical and environmental monitoring. Traditional mid infrared detection and imaging technology faces many problems such as low detector sensitivity and large size. Nonlinear frequency upconversion technology converts mid infrared signal light into near-infrared or visible light bands, which can achieve high-sensitivity detection using silicon-based detectors with small size and high quantum efficiency, providing a new technological approach for mid infrared detection and imaging. Numerous studies have shown that metasurfaces can enhance the interaction between light and matter in sub wavelength nanostructures, breaking through the phase matching limitations of traditional nonlinear optical parametric processes. However, existing metasurfaces typically rely on narrowband high-quality factor resonances to achieve local field enhancement, which poses significant challenges for the further development of ultra wideband nonlinear frequency conversion technology.

Figure (a) Metasurface structural unit; (b) Dielectric constant curve; (c, d) absorption spectra; (e, f) Localized fields at different wavelengths

Figure (a) 3160 nm; (b) 916 nm;  (c) 710 nm. Distribution of electric field Ez component; (d, e) Upconverted light intensity generated by different signal light and pump light; (f) Upconversion light intensity generated under different signal light intensities

In response to the above issues, the research group proposed a method of using gap plasma mode to achieve mode field overlap and broadband enhancement. By designing hyperbolic metamaterials (HMMs) composed of Au ZnO multilayer structures with triangular pyramid shapes, the ultra wideband nonlinear frequency upconversion technology was theoretically verified for the first time in the 3-5 μ m mid infrared band. The gap plasma mode in HMMs multilayer structure excites high-order narrowband resonance at near-infrared pump light wavelength, while the slow light effect generated by dipole and hyperbolic dispersion achieves ultra wideband near-field enhancement at mid infrared wavelength. The symmetry breaking of the triangular structure localizes these resonance modes at the tip of the structure, which not only enhances the localized field in the dielectric material, but also achieves mode field overlap at different signal and pump wavelengths, significantly enhancing the nonlinear frequency conversion process. Thanks to the slow light effect, manipulating the geometry and materials of the basic units of metasurfaces can adjust the above modes, thereby achieving frequency conversion processes at specific wavelengths. The research results provide new ideas for the development of nonlinear frequency conversion technology based on metasurfaces, and provide technical support for the research of new mid infrared optoelectronic detection systems. It has important application value in the fields of mid infrared detection, imaging, sensing, and communication.

Source: Xi'an Institute of Optics and Fine Mechanics