| This paper addresses the problems of near-infrared signals in satellite-to-earth optical communications being affected by the atmosphere,fast attenuation of optical links,unstable links,and lack of core communication devices in mid infrared space communications.To solve these problems,a 3.65 μm nonlinear magnesium oxide lightly doped lithium niobate ridge optical waveguide with high conversion efficiency is designed in this paper.And for the 3.65 μm mid infrared laser generated by this waveguide,the research of transmission characteristics and transmission comparison analysis in the multi-layer dynamic slope atmosphere were carried out.First of all,for the generation problem of high power 3.65 μm mid-infrared laser,this paper adopts a three-wave mixing wavelength conversion method based on first-order phase matching.Theoretical analysis of parameters affecting the efficiency of mid infrared generation such as temperature,crystal size,polarization period,wavelength conversion range,and quasi-phase matching receiving bandwidth.And carry out the electromagnetic wave transmission simulation,parameter optimization research.The optimal parameters such as the crystal length of 50 mm,the polarization period of 30.4 μm and the temperature of 51.3℃ are obtained.When the incident laser power is 1 W,a mid-wave infrared laser with a center wavelength of 3.65 μm and the linewidth of 6nm is generated in a bulk crystal with a cross-section of 1mm2,with a maximum output power of 0.3 W and a maximum conversion efficiency of 30%.Furthermore,a high refractive index magnesium oxide lightly doped lithium niobate ridge waveguide with a crosssection of 19.5 μm2 was designed to enable single-mode transmission of 3.65 μm mid-infrared laser in the waveguide.Compared to the bulk crystal,the output optical field energy was increased by three times.For the analysis of the influence of atmospheric turbulence on the 3.65 μm carrier in the free-space dynamic oblique transmission link,isotropic simplification is often used for the characterization of atmospheric turbulence characteristics,resulting in poor estimation accuracy of its influence.It is proposed to use a multi-turbulence power spectrum joint model according to different atmospheric levels,.A multi-turbulence power spectrum model is proposed for different atmospheric height layers,and the scintillation model of the uplink and downlink links in atmospheric slant paths is corrected using Rytov theory.By introducing parameters such as atmospheric turbulence anisotropy factor and zenith angle into the turbulence model,the accuracy and the universality of the model are improved.And based on the revised model,a simulation analysis of the influence of atmospheric turbulence on the transmission of 3.65 μm mid infrared laser was carried out.The results show that when the zenith angle is 30° and the transmission distance is 2 km,the scintillation indices of the 1.55 μm near-infrared and the 3.65 μm infrared laser are 0.02 and 0.0067,respectively,the anti-atmospheric scintillation property of 3.65μm mid infrared laser is 27.2%higher than that of near-infrared 1.55 μm near-infrared laser.This research has practical and guiding significance. |
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