长波红外与激光共孔径双模导引光学系统研究

Research on Long-Wave Infrared and Laser Common-Aperture DualMode Guided Optical System

为提高导引结构的特征分辨能力和全天候工作能力,提出一种长波红外与激光共孔径的双模导引光学系统设计方案,利用被动红外模块搜索目标,通过主动激光雷达模块锁定目标并精确制导。为解决导引头内光学系统尺寸受限的问题,以Ritchey-Chretien结构为共用部分,通过次镜镀分光膜实现长波红外(8~12μm)反射光路与激光(1.064μm)透射光路的组合,并分析了不同光学遮拦情况对非相干成像系统调制传递函数衍射极限的影响。展示了F数为0.98、光学遮拦比为1/3的共孔径双模导引系统的实例,使用多片折射镜片实现对主、次镜残余像差的补偿,利用光学被动式消热差方法完成-40~60℃范围的长波红外无热化,具有良好的热稳定性和可加工性,可为双模导引光学系统的分析与设计提供参考。

Objective As the optical technology develops,in order to adapt to complex and changeable battlefield environments,composite guided modes have received more and more attention.Longwave infrared(LWIR)/laser dualmode seeker can provide complementary benefits such as allweather operation,antielectronic interference,and high hit accuracy.Currently,commonaperture dualband systems with a laser of 1.064μm and an LWIR of 8-12μm mostly use a halfreflecting mirror to realize beam splitting.The image space resolution and field of view of the infrared optical system still need to be improved.Aiming at improving the feature resolution ability and allweather working capability of the guidance structure,this paper proposed a new dualmode guided optical system based on a secondary mirror splitting method.The passive infrared module was used to search for the target,and the active lidar module was utilized to lock the target and realize guidance accurately,and thus the highprecision scanning and patrol in a compact structure could be realized.Methods The RitcheyChretien(RC)structure was used as a common component to address the issue of the seeker's limited optical system size,and the secondary mirror was coated with a beam splitter film to combine the longwave infrared reflection optical module with the laser transmission optical module.In addition,the paper studied the initial structure solution method of the catadioptric system,as well as the effect of various optical obscuration conditions on the diffraction limit of the modulation transfer function of the incoherent imaging system.An illustration of a commonaperture dualmode guided system with an optical obscuration ratio of 1/3 and an Fnumber of 0.98 was presented.The residual aberrations of the primary and secondary mirrors were compensated for by using several refractive lenses,and an optical passive athermalization method was used to complete the longwave infrared athermalization in the range of-40-60℃.By using Monte Carlo analysis,the assembly tolerance and optical component tolerance were simulated.The resulting tolerance distribution was reasonable and workable.Results and Discussions According to the optical transfer function(OTF)of the annular obstructing optical system(Fig.4),a reasonable obstruction ratio was determined,and the lens aperture of the system with a small Fnumber and large aperture was weighed against the lightgathering ability of the optical structure.First,the secondary imaging structure was used to reduce the light height of the edge field of view,and the optical aperture after being obstructed was fully utilized.The longwave infrared imaging structure,with good image quality,consists of two reflectors and five refractive lenses(Fig.6),and the MTF of this structure at 42 lp/mm is higher than 0.32(Fig.7).The reflectivity in the longwave infrared band exceeds 90%,and the transmittance in the laser band exceeds 80%,which allows for highprecision target scanning and precise guidance.Then,through the selection of optical and structural materials and the distribution of optical power,the athermalized design of the longwave infrared module in the temperature range of-40-60℃was realized,which shows good thermal stability(Fig.11 and Fig.12)and processability(Table 3).Finally,this paper kept the infrared optical module's common aperture part,used the left side of the secondary mirror as a refracting material,and optimized the design of the laserreceiving optical module.The light in the receiving system with a laser of 1.064μm was parallel after optimization(Fig.9),and a narrowband filter was added to avoid wavelength shift caused by largeangle incidence.The light of all fields of view was focused within 0.5 mm of the detector target surface(Fig.10),which can enhance the signaltonoise ratio of the laser module.Conclusions A design method for the dualmode guided optical structure was proposed and demonstrated in this paper.In addition,the effect of different obscuration ratios on the MTF diffraction limit of the catadioptric optical structure was studied,and a dualmode guided imaging system with a small Fnumber and a common aperture of an LWIR of 8-12μm and a laser of 1.06μm was designed.The method of secondary mirror splitting simplifies the system structure effectually,and the secondary imaging structure increases the field of view and reduces stray light.In order to enhance the signaltonoise ratio effectively,a narrowband filter was introduced into the laser module's smallangle light.The longwave infrared optical module has good imaging quality in the 4°×3°field of view,and the modulation transfer function(MTF)at 42 lp/mm is higher than 0.32.The optical obstruction ratio is only 1/3.Through the combination of different materials,an athermalization design under a temperature of-40-60℃was achieved.The overall size is reflected by only 98 mm(length)×70 mm(width)×70 mm(height),and the structure is compact,which meets the application requirements of lightweight and engineering and can provide a certain reference for the design of multimode guided optical structures.