Research On Focal Depth Extension Characteristics Of Infrared Systems Based On Wavefront Coding

In order to enlarge the focal depth of the traditional optical system,the general way is reducing the F number of the optical system.However,that will result in the reduction of the entrancing energy of the imaging light,at the same time result in reduction of the angle resolution and SNR,unable to obtain high frequency information of the image effectively.The wavefront coding technology as a new imaging technology,including optical image and digital image processing,has a great advantage in enlarge the focal depth of the optical system.Compared with the traditional optical system,the wavefront coding system has an order improvement in enlarge the focal depth of the system.However,as a cross discipline,there are many characteristics of the wavefront coding technology don't known by the people.This paper is devoted to the study the wavefront coding system with cubic phase mask,hope that can make some contributions to the design,assembly and image restoration work of wavefront coding system with cubic phase mask,the primary research contents and innovations of this paper are as follows:1)Combined with the cubic phase mask encoding theory,analysis the deviation characteristics of the point spread function of the encoding system which with cubic phase mask.Calculation the relationship of phase mask parameters with defocus amount when the point spread function without deviation,at the same time,analysis the Strehl ratio of on-axis when wavefront coding system on focus and defocus condition.Point out the reasons of on-axis Strehl ratio is not suitable for phase mask optimization process of wavefront coding system,thus leading to off-axis Strehl ratio and simultaneously analysis the characteristics of off-axis Strehl ratio.2)Proposed the phase mask parameters optimization method which based on off-axis point Strehl ratio,with the help of the optical system design software(CODE V)and data processing software(MATLAB),using the genetic algorithm to realize the phase mask parameters optimization which based on off-axis point Strehl ratio.Using this way optimization the classical cubic phase mask and variations of the cubic phase mask.Give the wavefront coding system design ideas and design process.3)In order to engineering the wavefront system with cubic phase mask,analyzed the tilt effect of the phase mask in the actual lens assembly process,and established the mathematical model by means of the coordinate transformation.At the same time,deducing formula of different temperature conditions phase mask profile changes,given the profile changes between different temperature conditions.In the last of this part,compare the result of imaging performance of the conventional optical system to wavefront coding system with cubic phase mask at different temperature.4)After optimized,a long wave infrared system is fabricated and assembled.The optical path is set up and obtained the images of different distances,after that restored the encoding images.By contrast of wavefront coding system images and conventional optical system images,confirmation the depth of field of wavefront coding system has been greatly improved.