Study On Design And Application Of Optical Imaging Systems Based On Micro Lens Arrays

Optical systems play important roles in image identification,astronomical observation,medical instruments and weapon guidance as the extension of human vision.With the development of science and technology,the requirements of system volume,integration level,field of view and accuracy in optical system become higher.The traditional systems with single aperture can hardly match these requirements because of the limitation of diffraction limit and structure characteristics.It is necessary to apply new optical theories and imaging modes.The micro lens arrays which consist of serial of micron to millimeter sized micro lenses have advantages of small sized,high integration,easy machining,little transmission loss and special functions,and they have wide application prospect in optical systems.This paper studies on two typical application of micro lens arrays in light field imaging and compound eye imaging systematically.The light field systems based on planar micro lens array can record the location and direction information of the incident light rays synchronously,the information is stored as 4-dimensional data and can be reconstructed as large depth of field image.In another word,the light field systems can “capture first,focus later”.The size of the micro lens,the fill factor and the uniformity in the micro lens array effect the quality of captured light field information immediately;The compound eye systems based on curved micro lens array break through the limitation of single aperture optical systems and extend the field of view largely by simulating the structure of insect eyes.The optical surface structure and the arrangement of the ommatidia in the curved micro lens array affect the imaging quality and the field of view directly.In this paper,the design and fabrication of micro lens arrays have been studied based on the technical requirements in two typical application areas,and the performances of the imaging systems have been improved.The theories of light field imaging have been analyzed and the shortage of the utilization of the image sensors in existing system have been pointed out.To increase the light-use efficiency,a new system with overlapped square aperture micro lens array and a customized square diaphragm has been presented;The array is made by microinjection moulding,and the mould is processed by ultra-precision milling;The new imaging system has been set up and captures the 4-dimensional light field data.With the 4-D data,the multi-view images,the multi-depth of field images and the super resolution images are reconstructed successfully.The experiment shows that comparing with the traditional light field system,the new system increases the fill factor by 27%,increases the light-use efficiency by 96%,increases the range of depth of field and viewing angle by 1.4 times.The super resolution image also has more details.Based on the nature structure of insect eyes and optical theories,the functional relationship among the field of view,optical axis angle and overlapping area is established in mathematic;A single layered compound eye with 7 ommatidia applying freeform optical surfaces is developed and achieves the field of view of 40°.The functional relationship in compound eyes has been verified by this system;Combining the advantages of existing compound eye systems,a curved 2×8 compound eye system is designed and manufactured,which is close to the structure of insect compound eye.Sixteen 1/3 inch CCD sensors are assembled as a curved 2×8 image sensor array.And a curved 2×8 single layered micro lens array is designed and manufactured.All the lenses are perpendicular to the corresponding CCD sensor,which eliminate the off-axis aberration.The application of optical freeform surface and aspheric surface guarantees the imaging quality of single layered lens.And the single layered lens array reduces the difficulty of manufacturing and assembling of compound eye system.The system achieves high quality image capture in the field of view of 180°×75° with no gap.This paper studies on the design and manufacturing of typical structural micro lens arrays,the system theories and optical mechanism in imaging applications are also been studied.The performances of optical systems with large field of view and large depth of field are improved by new manufacturing method,precise optical surface and reasonable system structure.The development prospect,technical advantages and difficulties of micro lens arrays are defined,which provides guidance and reference for future work.