Study Of Plenoptic Camera Wavefront Measurement And Application

The air refractive index varies randomly due to the influence of atmospheric turbulence.When propagating through the atmosphere,the wavefront of the light wave will be distorted.It leads to a blur image of the observation target on the imaging device.Adaptive optics is the most effective technique to overcome the influence of atmospheric turbulence,and wavefront sensor is one of the key components of the adaptive optics system.At present,several wavefront sensors are widely used,such as Shack-Hartmann wavefront sensor,pyramid wavefront sensor and curvature sensor.As a new technique of wavefront sensing,plenoptic camera is getting increasing attention of scholars.It has a simple optical structure,high light energy utilization efficiency and high accuracy.The plenoptic camera can avoid the overlapping and crossing of sub-images due to its unique optical structure.Therefore,it has great advantages in wavefront sensing of extended sources.This paper mainly investigates the key theory and technique of plenoptic camera in wavefront sensing.The dissertation's main work is listed as follows.Firstly,the wavefront sensing technique of plenoptic camera is investigated in depth.By starting from the optical structure of plenoptic camera,the characteristic of the light field captured by plenoptic camera is analyzed.Based on it,slope measurement formulation is derived and slope filtering characteristic of micro lens are analyzed.At the same time,various error sources are discussed,the influence of various factors on the accuracy of measurement is investigated,and the approximate error calculation formulas are derived.Work above lays a solid foundation for further research.Secondly,the wavefront sensing system based on plenoptic camera is established,and its wavefront sensing performance of point sources and extended sources is studied in depth.Specifically,the performance is evaluated by several parameters including linearity and accuracy.The result shows that the linearity is poor in case of wavefront sensing of point sources and is associated with lens size.In contrast,plenoptic camera has a better linearity when sensing wavefront of extended sources.As for sensing point source wavefront,the methods of modulation and defocusing are put forward to improve the linearity.The modulation method is more effective,while the defocusing method has simple structure and needs no extra optical equipment.As for sensing extended source wavefront,the effects of reference image size,target type and assembling error on detecting accuracy are analyzed.The possibility that the number of plenoptic camera sub-apertures can be adaptively adjusted is verified.The computational complexity of image phase method in image displacement estimation is rather extensive,thus a more efficient correlation spectroscopy phase method is proposed.Result shows that accuracy of both methods is equivalent,while computational complexity of the former is reduced to that of centroiding method.Furthermore,plenoptic camera and traditional Shack-Hartmann wavefront sensor are carefully compared.It shows that accuracy of both matches,while signal-to-noise ratio of plenoptic camera is higher,making it suitable for detecting dim objects.Finally,the theory of plenoptic camera wavefront sensing technique is studied.By setting up adaptive optics simulation system based on plenoptic camera,control capability of the system and detecting ability of plenoptic camera in closed loop is researched.Theories of simulating various modules of adaptive optics system are studied,the corresponding simulation models are established,and an adaptive optics simulation system of 61 units is then set up.Closed-loop control algorithm is studied;modes of deformable mirror are discussed and theory and method of mode choosing are analysed.A number of closed-loop imaging simulations of point and extended sources are carried out.It shows that it is practicable to use plenoptic camera for wavefront sensing in adaptive optics systems,especially in the case of extended objects detecting.