| Optical sparse aperture(OSA)telescope is the trend of next-generation deep space exploration.As one of the forms of the optical synthetic aperture system,the OSA imaging system,by using separated sub-apertures,can improve the resolution equivalently the large aperture system.Compared with single-aperture system,the system has advantages such as smaller-scale mirrors,changeable aperture arrangement,less weight and flexible baseline.Meanwhile OSA system is supposed to meet the requirement of sub-apertures in common phase.As the result of that,the study of combining-beams error becomes necessary for the system.This thesis focuses on combining-beams errors,by analyzing the point spread function(PSF),specifically researching the relationship between combining-beams errors and resolution of OSA system.With different fill factors and baseline lengths,this study model sparse systems,and the effects of them on the PSF of the system are analyzed.The simulation results show that the smaller the fill factor is,the less frequency components of optical information can be transmitted,the greater the absence of the mid-frequency band of the system,and the lower the imaging resolution.The longer the baseline length,the higher the side lobe light energy,and the greater the visibility of the fringes.In this thesis,the system with piston error and tilt error is modeled and theoretically studied.PSF and MTF of the system under different error values are obtained by simulation.The results show that PSF is a periodic displacement,and the period is equal to wavelength of the incident light,and the displacement direction is consistent with the baseline direction.At the same time,the imaging resolution of plane target will decrease with the increase of piston error.In addition,the tilt error causes the non-uniform distribution of PSF,and the midfrequency missed.Meanwhile,the absence of the mid-frequency increases with the increase of the tilt error value.Apart from what have mentioned above,an experimental set for OSA system is built to conduct experimental research on beam combining errors.By using Spatial Light Modulator(SLM),the experimental results are consistent with the simulation results.Loading a gradient grayscale picture,the SLM simulate tilt error,and PSF changes non-uniformly.In addition,the effect of the piston error on the imaging effect is studied experimentally,and the results show that the piston error will reduce the restoration resolution. |
