Design and research of long-infrared dual-wavelength confocal metalens

Multi-wavelength confocal lens is an indispensable part of optical system, the traditional optical confocal systems often by adding a certain number of optical lenses, or use a different combination of optical lenses of different materials to implement multi-wavelength confocal, which is bound to make the system has a larger volume and weight, and which is difficult to meet the requirements of high integration and miniaturization of the system. As an optical element composed of two-dimensional planar subwavelength micro-elements structure, the metalens has the advantages of flatness, ultra-thinness and regulating light waves, and has great potential application in highly integrated and miniaturized optical confocal systems. According to relevant literature reports, it is known that the existing research schemes of multi-wavelength confocal metalens have some shortcomings, such as relatively complex structure, relatively low focusing efficiency. In this paper, a kind of metalens composed of simple micro-elements structure is proposes and designs, which can simultaneously realize the long infrared dual wavelength confocal function. Based on the generalized Snell's law and the transmission phase modulation mechanism, a scientific evaluation function is established to select the optimal array of micro-elements structure to form a metalens. With the elliptical nano silicon column in the simple micro-elements structure, the wavefront phase of the long infrared dual wavelength in the orthogonal linear polarization state can be independently and efficiently adjusted, while reducing the wavelength crosstalk and improving the focusing efficiency. The design results show that the proposed metalens achieves dual wavelength confocal with a wavelength of 10.6μm and 9.3μm, and has a high focusing efficiency, The focusing spot is close to the diffraction limit. Quantitative analysis of the redundancy of the structural parameters of the metalens micro-elements structure is made, and the trend of its influence on the focusing efficiency and the allowable deviation range of the micro-elements structure parameters are obtained, which provides a theoretical basis for further precision control of device fabrication. The matalens designed in this paper is expected to meet the requirements of integration and miniaturization of long infrared optical confocal system, and has important application value in laser surgery, industrial cutting and welding and other fields.