| Optical filters designed based on metal micro-nano structures have the advantages of exceeding the diffraction limit,spectral modulability,optical stability in complex environments and compatibility with existing micro devices in the application of the new generation of optical devices,and this has already been the focus of research.The midinfrared wave in the atmospheric window of 3-5 microns provides a new spectral platform for the field of photoelectric detection.In recent years,researchers have conducted relevant studies on the spectral characteristics of metal surface plasmons in the mid-infrared band.It is still a big problem in this field to design the micro-nano structure of precious metals to achieve effective modulation of transmission spectral information.At the same time,if the research is to be applied commercially,it is necessary to design more than the traditional technical scheme to improve the filtering performance and adopt appropriate micro and nano processing technology to reduce the experimental cost.In this paper,theoretical model design and experimental research are carried out for these contents.Firstly,in the aspect of theoretical research,based on the basic principle of surface plasmons,the transmission spectrum of metal micro-nano hole array filter structure is analyzed and simulated.The effects of hole structure shape and size,metal film thickness,light source radiation angle and metal material on spectral transmittance characteristics in the middle infrared 3.0～5.0 μm band were analyzed.The results show that in the aspect of structure shape,the difference of the half-width,central wavelength and transmission intensity of the transmission spectrum between the circular hole and the square hole is very small,and the average difference of the three parameters is 5.1%,5.8% and 1.8%respectively;The increase of metal film thickness leads to the decrease of spectral transmission intensity;The radiation angle of the light source mainly affects the transmission intensity,and has no effect on the peak position of transmission;In terms of metal materials,the transmission intensity of Au and Al is lower than that of Ag.Moreover,based on these theoretical level simulation data,this paper establishes mathematical relationships between different parameters of the design model,which provides the conditions and foundation for achieving high transmittance and modulability of multichannel spectra in the theoretical simulation stage.Secondly,in the aspect of experimental exploration,based on the results of simulation design,the preparation and characterization of metal micro-nano structure filter samples and the transmission spectrum testing and analysis were carried out.The experimental preparation of the micro-nano structure is mainly carried out according to the period of 4.0μm and 3.0 μm of the simulation design,and the spectral test of the prepared structure samples is carried out.Transmission intensity spectral line results of the single-channel micro-nano structure filter prepared by the experiment are consistent with the theoretical simulation results,and the main error is in the transmission peak position,which is caused by the uneven exposure in the experimental photolithography process.In addition,the simulation parameters are adjusted according to the size of the prepared sample,and the error is simulated and analyzed iteratively.The simulation results are compared with the measured transmission spectrum,and the matching degree between the spectral lines is improved.In this paper,based on the super-transmission characteristics of surface plasmons,the medium-wave infrared metal micro-nano structure filter is designed and prepared,and its transmission characteristics are tested and analyzed,and it is proved that the micro-nano structure designed in this paper has the function of transmission spectrum modulation.Which has important theoretical value and practical significance for the further application and development of metal micro-nano structure in optical devices. |
