Large depth of field imaging technology & it’s phase shift control

The role of cubic phase plate in large-depth-of-field diffraction limited system with CCD detector was discussed and the special phase shift phenomena caused by the cubic phase plate was studied.Mathematic functions indicating the relation between axial desfocus parameter ψ,cubic phase plate shape constant α and modulation transfer funetion(MTF) and image shift variable s were deduced.Spoke images for standard imaging system and that with large depth of field were shown when defocus variable w equals to 0,50,150 and 300 times wavelength respectively.Changing optical transfer function and reducing its sensitivity to axial defocus parameter,depth of field for imaging system was enlarged.Along with its enlargement,phase shift appeared simultaneously,which is related with both the extending ratio for depth of field and the constant for cubic phase plate.Thus phase shift could be very small and a satisfactory image might be achieved when the extending ratio was limited to a certain suitable range and a reasonable constant for cubic phase plate was chosen.