Data Processing And System Calibration On Fiber Point Diffraction Interferometer

Point Diffraction Interferometer-a physical idea ,is invented by Smartt and Strong in 1972,advanced by Smartt and Steel,and used to test astronomical telescope,it has simple structure and has not special demand to source.recently.with the development of fiber's manufacture and coupling technology.the simple modern fiber's center is smaller than before,this make it possible to progress Fiber Point Diffraction Interferometer(PDI),in addition to test convergent wavefront ,it can test the reflective concave.the excellence of PDI is that it does not need standard mirror.in intereference testing,the standard mirror is the main reason which limit the improvement of precision ,PDI can avoid difficulty to provide the wide future for high precision testing .PDI, which produce the standard sphere wavefront, is an instrument which realize the phase shifting with piezoelectric transducer (PZT),and collect the interferogram With CCD,in this paper,a adjusting methord is described ,then data processing is obtained.First.adjust the fiber to get the interferogram,use the four-step phase shifting method control the change of phase,achieve phase shifting .In data processing,take the PZT'linear influence into account, calibrae the PZT.Unwrapping the phase,gain the continuity,get the actual phase.Analyzing the data with zernike orthogonal methord,fit polynomials that are not orthogonal over the data points,through Visual C++ program,obtain polynomial parameters .calculate the shape of the surface,compare the result with ZYGO,then achieve the better experimental result.