Research On Key Technology Of Adaptive Optics Based High Resolution Micro-imaging System

The adaptive optics (AO) is a new technology which views the optical wavefront aberration asresearch object, corrects the aberration of optics system real-timely and allows the optical imagingsystem performs well in different working conditions. The development of the technology makes itpossible to correct human eye aberration and image vivo human eye retina with high resolution. Basedon the AO principle and visual optics theory, the related principles, key technologies, software andhardware technologies etc. in micro-imaging system were studied. Combined with the correction rangeand capability of micromachined membrane deformable mirror (MMDM), the dynamic andcombination characteristics of the human eye aberration were studied, based on which the aberrationcorrection control model were optimized to improve the performance. On the basis of the obtained AOretina images, the image restoration technique was employed to eliminate the influence of aberration onimage quality staticly to obtain retina images of high resolution. Finally, a set of high resolution retinaimaging system which can achieve the clinical application requirement effectively was established. Themain research contents are listed as follows:(1) The characteristics of human eye aberration and aberration combination were studied. Therepresentation model of human eye aberration was established with Zernike modes. The dynamiccharacteristics of human eye aberration, relationship between Zernike aberration and optical quality ofhuman eye, and influence of different pupil diameter on human eye aberration and optical quality wereanalyzed systematically. The linear conjugated combination models of Zernike modes were proposedthrough analysis of the correlation among Zernike modes, and influence of the novel model on opticalquality was studied emphatically.(2) The aberration measurement principle and wavefront reconstruction algorithm of Hartmann-Shack (H-S) wavefront sensor were studied. An adaptive spot centroid detection method withpositioning spot regions dynamically, segmenting threshold levels dynamically and locking optimaldetection window was proposed according to the structure features of H-S wavefront sensor anddistortion characteristics of the actual human eye spot pattern. In view of the wavefront reconstructionmodel with Zernike modes, the SVD and LGRE based wavefront reconstruction algorithms wereproposed in order to meet the real-time requirement in AO system and high precision in AO imagerestoration respectively.(3) The influence function, wavefront compensation and aberration correction of MMDM werestudied. According to the SVD based principal component analysis on influence function, the mirrormode aberration with poor correction performance was filtered by the method of low-rankapproximation of influence function matrix. The common solving model of voltage control signal for compensating aberration was established, based on which performances of OKO and BMC deformablemirror were analyzed. The compensation and correction ability of the deformable mirrors on Zernikemode aberration and Thibos model human eye aberration were further investigated, which provided thetheoretical method for choosing the deformable mirror for the imaging system.(4) The closed-loop control model of AO system was established. According to the automatic controltheory, AO continuous and sampling system models were proposed. Performances of the closed-loopsystem of different controllers, namely pure integral, proportion integral and Smith pre-compensationcontroller based on the continuous system and dead beat controller based on the sampling system, wereanalyzed. According to the modern control theory, the state space analysis based AO discrete systemmodel, AO state space model and Kalman filter based LQG optimization control model were proposed.The aberration correction algorithms based on the pure integral, proportion integral, Smithpre-compensation and dead beat controller were designed and the dynamic aberration correction withhigh bandwidth was realized both in simulations and experiments. The aberration correction algorithmbased on the LQG optimal control was further designed, the feasibility of which was also verified bysimulation.(5) The obtained images from AO system were restored for higher quality. The Semi-IBD restorationalgorithm, making full use of the residual aberration, for AO image was proposed. The new algorithm,utilizing the relative accurate initial estimate of image and PSF and employing frequency-domainconvergence criterion with internal and external circulation iterative, PSF frequency-domain bandwidthconstraint and PSF space support automatic adjustment, provided good performances in the tests forretina images with simulation degrading and ones from actual subjects.(6) The AO based high resolution micro imaging system prototype was developed and tested by therelevant state agencies. The optical, structure, electrical and software system of the imaging systemwere designed. Property tests and experiments were carried out and jobs for combining thetechnologies of AO and retina imaging were finished. Testing results form relevant state agenciessuggest that the distinguishing distance on the retina is about2.36μm, the field angle is about±3.0°×±3.0°, the fact enlargement ratio is about8.03, the frequency of measuring and correcting humaneye aberration is11~15Hz, the residual aberration is below0.1λ, the high resolution retinal images canbe obtained.