Research On Design Technology Of Off-axis Reflective Optical System With Freeform Surface

Space optical communication is a kind of communication mode which uses optical wave as carrier to realize wireless transmission of data and information in space.Because of its advantages of high transmission rate,strong anti-interference ability and confidentiality,many countries actively carry out research on key technologies of space optical communication,and many sets of space optical communication terminals have moved from experimental research stage to practical application stage.With the success of Falcon 9 rocket to send 60 satellites(Starlink Program)into space and the development demand of communication technology,it is the general trend to build a global space optical communication network,which brings opportunities and challenges to the development of space optical communication terminals.In this trend,the space optical communication terminal must first meet the Low SWaP(size,weight,and power)index to realize the requirements of space application for payload miniaturization,lightweight,and low power consumption.Optical antenna is one of the core components of optical communication terminal,which is mainly responsible for signal transmission and reception.Its performance will have a huge impact on the structure and performance of space optical communication terminal.However,the traditional optical antenna mostly adopts the structure of focusing and collimating the coaxial reflective optical system,which has the central blocking,low communication efficiency and relatively small effective field of view,resulting in the structure form of coarse and fine tracking separation adopted by the ATP system in the space optical communication terminal,which is relatively complex.Therefore,improving the efficiency of optical system and increasing the effective field of view of optical system become one of the key development directions of optical antenna.In recent years,freeform surface has been widely used in the field of imaging optical system,which is of great significance in improving the image quality of edge filed of view(increasing the field of view)and reducing the volume of the system.In this paper,the design of off-axis two mirror afocal optical antenna based on freeform surface is proposed.In this paper,an off-axis two mirror afocal optical system based on freeform surface is designed,which improves the optical efficiency through off-axis structure,increases the field of view through the introduction of freeform surface,in addition,uses the afocal structure,which can save the subsequent collimation optical group and reduce the optical length of the optical system.The design results show that the system has high imaging quality in a large field of view.Aiming at the problem of off-axis two mirror alignment tolerance analysis,an off-axis two mirror alignment tolerance analysis method based on vector aberration theory is proposed,and the mechanism of secondary mirror misalignment(alignment error)on the wavefront aberration of the system is revealed.The simulation results show that this method has a certain guiding significance for the tolerance allocation of secondary mirror assembly.In view of the problem of freeform surface machining and inspection,this paper calculates the relevant processing parameters,formulates the optical precision machining process,and defines the inspection means,which has certain guiding significance for the secondary mirror machining.