Study On Key Technology Of Phased Telescope Array Imaging

It can be found from the Rayleigh criterion that the larger the telescope aperture,the higher the spatial resolution at a constant wavelength.It is difficult for conventional monolithic telescopes to meet the demands of the high resolution in varied scientific fields such as deep-space exploration,remoting sensing,and so on,since the increasing of the aperture is limited to the manufacturing material,cost,mass,payload volume,and so on.The phased telescope arrays utilizing several phased small apertures to achieve the high resolution equivalent to a large aperture,have advantages of small volumes,low costs and flexible forms of realization,which will be one of the main means to achieve high resolution imaging in the future.This thesis performs deep research on the key technologies of the phased telescope array,such as the sensing and correction of both co-phasing errors and sub-aperture aberrations,and image restoration for Fizeau mode,as well as the correction of co-phasing errors,and wide filed imaging for Hypertelescope mode.The following works have been done.First,the object-image relationships for both Fizeau and Hypertelescope telescope arrays have been studied,with their corresponding mathematic models built.By means of simulation,we have discussed the influences of the phase errors for Fizeau telescope arrays,and analyzed the direct imaging principle and the limitations of the field-ofview for Hypertelescope arrays with pupil densification.The theoretical research lays the foundation for the following work.Secondly,a method of piston correction using the stochastic parallel gradient descent(SPGD)algorithm has been proposed.Based on simulation setup,the proposed method achieves piston corrections for both Fizeau and Hypertelescope telescope arrays.Next,we propose a new method for wavefront sensing and image restoration,termed spatial modulation diversity technology.To start with,it is demonstrated in traditional single-aperture systems.Then inspired by the structure of multi-aperture systems,we develop the technique for Fizeau telescope arrays via shutter modulation.For imaging faint objects,the method succeeds in restraining the photon noises and improving the accuracy of the sensed wavefront and quality of the restored image by being combined with the blocking-matching and 3D filtering algorithm.Then,the algorithm of the incoherent Fourier ptychography is improved by embedding a mathematic model built for estimation of the optical transfer function.After testing the validity of the modified algorithm in single-aperture systems by simulation,we propose an active Fizeau imaging technique using transmitter modulation with that algorithm,capable of digitally correcting sub-aperture aberrations and co-phasing errors,and restoring images with higher resolution.This technology makes it possible to modulate both the paths of transmitters and image receivers,providing a new insight to address the crucial problems.Furthermore,we develope a Fizeau binocular telescope array in our laboratory,which is phased by SPGD close-loop algorithm.It is verified based on the testbed that the spatial modulation diversity technonogy can sense the sub-aperture aberrations and restore high-quality images.Besides,we introduce and analyze the interesting phenomenon of the spatial frequency shift appearing in the procedure of the system development.Combining the horizontal two telescopes with another single one generates a Golay-3 telescope array.From experimental results,it can be seen that it is available for the system to synthesize both point sources and extended objects.This phased Golay-3 telescope is the first Fizeau interferometric imager in China.To obtain higher resolution,future phased telescope array for deep-space exploration will develop towards larger arrays with long baselines,to which Fizeau imaging mode doesn't apply.For such long baseline arrays,Hypertelescope imaging mode with pupil densification has shown the potential to realize direct imaging.However,though providing very high resolution,Hypertelescope is limited to a narrow field-of-view.To address the physical limitation of the field-of-view,a multiplexing strategy of optical design is proposed.The microlens arrays are used to sample a wide field,making it available to realize independent tilt-tip and piston correction in each sampled field channel.Such a Carlina Hypertelescope array with multiplexed fields has been established in Zemax.Several independent working fields generated by the Zemax optical model can be received by the same science detector,thus achieving discrete wide field imaging.