Research On The Aberration Of DMD In Coded Aperture Imaging Spectrometer Optical System

The coded-aperture-spectral-imaging-systems(CASIS)which has the advantages such as high optical flux,high signal-to-noise ratio and flexible coding mode,has become a research hotspot in the field of the spectrometer.With the rapid development of the microelectro-mechanical technology in recent years,the digital micromirror device(DMD)has replaced the traditional mechanical template and liquid crystal spatial light modulator with the high code error rate and low optical flux in the CASIS and has become the best choice for the coding aperture device.Therefore,the DMD can make great contribution to the high optical flux and the high signal-to-noise ratio of the CASIS.However,the DMD is different with the plane mirror which has only one rotation axis.Each micromirror on the DMD surface rotates around its own rotation axis,which results in the optical path difference(OPD)between the light incident to the DMD surface with different image heights,and leads to a series of aberrations.If the aberration in the system is too large and not compensated,the resolution of the system will be reduced and the number of spectral channels will be decreased.That will ultimately affect the working efficiency of the whole system.At present,the main research of the CASIS is about algorithm implementation,while the optical system of the CASIS has not been deeply studied and discussed.Based on the wide application prospect of the CASIS and the research blank of the DMD aberration in this optical system,this thesis analyzes and studies the DMD aberration characteristics under different working conditions,the image quality evaluation and the aberration compensation method.The main work content includes the following aspects:Firstly,the working principle and the modeling method in the optical system of the DMD are studied in detail.By the means of strict ray tracing,theoretical derivation and simulation,the relationship is analysed between the off-axis optical path difference(OPD)of the different image height optical rays on the DMD surface and the incident angle,the DMD pixel size with the DMD tilt angle.Based on this,the focal depth is used as the criterion to evaluate the influence of the off-axis OPD caused by the DMD to the final imaging quality of the system.In addition,the OPD compensation method is also researched and verified through the experiment.Secondly,considering the adjustment angle error of the DMD when the system is fabricated,this thesis also analyzes the relationship between the off-axis optical path difference(OPD)of the different image height optical rays on the DMD surface and the incident angle,the DMD pixel size with the tilt angle.Moreover,the aberration characteristics of the marginal rays are also analysed and researched,that can be described as coma and defocus.Finally,the DMD optical module of the CASIS is designed in the thesis.Through the design progress and result,it is verified that the effect of the DMD to the imaging quality of the optical system and the actual result of the image plane tilt to compensate the aberration.The content of this thesis has certain application value for the design and fabrication of the DMD-based CASIS.