Design Of Common-aperture Optical System For Multi-band Spectral Reception And High-speed Imaging

A common-aperture optical system for multi-band spectrum receiving and high-speed imaging is designed in this paper.The front end of the optical system adopts the classical Cassegrain structure.The back end is the refractor group of the visible-light high-speed imaging system and the spectral receiving system.The two parts are connected with each other by a beam-splitting system.The system requirement is that when the environmental temperature is-20℃～50℃,visible-light high-speed imaging and multi-band spectrum receiving(0.2μm～0.4μm 、0.4μm～0.76μm and 0.76μm～2.5μm)can be realized for flight targets with diameter 0.5m at a distance range of 0.5km～1.5km.Firstly,the optical basic parameters of the visible-light high-speed imaging system and each spectrum receiving system are determined according to this requirement.A Cassegrain system is constructed based on aberration theory,which is used as the common-aperture part of the multi-band spectrum-receiving and high-speed imaging system.At the same time,a beam splitting methods by a prism system and a plane parallel plate system are proposed for the wide spectrum.After comparing the two methods,the beam splitting method by a plane parallel plate system with higher engineering feasibility is adopted.The problem of astigmatism caused by tilted plane parallel plates is solved successfully by utilizing two cylindrical lenses in the visible-light high-speed imaging system.The deviation of optical axis caused by the tilted plane parallel plates is compensated by adding a reverse tilted plane parallel plate.After the visible-light highspeed imaging system is optimized with thermal aberration,the MTF values of each field of view in the visible light high-speed imaging system are all greater than 0.5 at Nyquist frequency 35lp/mm.This result is extremely close to the curve of diffraction limit.Then,the spectrum-receiving systems are designed while the parameters of primary and secondary mirrors remain unchanged.The spectrum-receiving systems meet the requirements of fiber coupling.The tolerance analysis of the visible-light high-speed imaging system and the spectrum-receiving system shows that the system can meet the requirements of actual fabrication and alignment.The structural design of Cassegrain system,the lens hood,beamsplitting system and refracting lens groups for each branch are also completed by utilizing Solidworks software.The thermal analysis of the primary and secondary mirrors show that in the temperature range of-20℃～50℃,the maximum deformation amount of the primary and secondary mirrors are both less than 9μm,which meet the requirements of surface accuracy of primary and secondary mirrors.