Research On The Key Technologies Of Extending The Depth Of Field With Wavefront Coding And Its Application In Micro-imaging System

When the distance between the object and image does not meet the conjugate relationship to an ideal optical imaging system,the beams at the original conjugate image position cannot focus,but form a diffused spot and the image becomes blurred quickly which cause the loss of detail and texture.The image with large depth of field or focus contains more information.Therefore in current research and industrial production,the extended depth of field or focus of optical imaging systems has been an active research topic for optical designers.In the past the methods of the extended depth of field such as pupil filtering method is at the cost of system resolution,normal image synthesis methods using the complex synthesis algorithm,large amount of calculation and increases the running time of hardware.However the newly emerged method of the wavefront coding(WFC)technology to extend the depth of field has solved the contradiction between the resolution and depth of field,the research of the wavefront coding technology,has been widely concerned,great progress has been made in theory and technical research meanwhile which has been widely used in machine vision,biological or medical microscopic imaging,infrared imaging and other field.WFC imaging technology is two steps imaging which combined optical design and digital imaging restoration.WFC is that modulate wavefront by adding a special pure phase mask on the pupil of the optical system,which makes the optical transfer function(OTF)and point spread function(PSF)insensitive to the object distance's change in a large depth of field of the optical system.Thus,we get a series of consistent middle blurred images and restore them to final sharp images by the digital image decoding technique.This paper carried out three related key problems to research on the present WFC technologies:the wide field effect of WFC system,a new type of tunable phase encoding mask,WFC microscopic imaging system experiment.This paper elaborates the analysis and solution of the above key technologies of WFC from theoretical analysis,system design,software simulation,imaging experiment and so on.The main research works are summarized as follows:First,it establishes an unified evaluation system to eight kinds of one-dimensional separable non-rotational symmetry phase mask.It has analyzed and evaluated from two indicators Hilbert space angle and the modulation transfer function(MTF)curve containing area and has gotten a large number of reliable analysis data;the wide spectrum imaging characteristics of cubic phase mask(CPM)system is analyzed and measured the degree of deviation of the point spread function(PSF)of various wavelengthes through the calculation of phase deviation;it analyzes the defocus MTF characteristics of CPM and the traditional system and the phase mask parameter influence to the extension of the depth of field;it has compared the effect of the extension of the depth of field of the CPM?polynomial phase mask and high power phase mask.Second,the structure of two symmetrical CPM structure is put forward to solve the large field of view effect of WFC system.For the first time it has been using WFC technique in ultra wide angle imaging lens and design the ultra wide angle WFC system;it has simulated the system by using the designed phase mask and using the two symmetrical CPM structure which can solve imaging difference effectively of the meridian and sagittal direction which caused by large field of view and also shows the good capability of extending the depth of field.Third,It puts forward new tunable cosine phase mask based on the original theoretical analysis of tunable phase mask.It analyzed the character of defocus insensitively and tunable of the frequency bandwidth of the new cosine tunable phase mask under different displacement combination.The simulation results show that the function of bandwidth control of new system is more flexible,and easier to institutions requirement.Forth,based on the current inexpensive domestic Phoenix 195 biological microscope,it designs a 10X WFC micro-imaging system and build an experimental platform for WFC system and verified the effectiveness of WFC technique,analyzes the imaging consistency of spatial and frequency domain of WFC micro-imaging system.The experiment results show that the focus of field of WFC system is 15 times compared with the original 10X microscopic system.