<title>Hybrid diffractive refractive broadband design in visible wavelength region</title>

Abstract

The diffractive optical element (DOE) is modeled as an aspherical thin lens with infinitely large index which can be implemented in commercial lens design software. The corresponding relation between the aspherical coefficient and the DOE phase profile is studied. Broad-band achromatic doublet and triplet designs in the visible wavelength region are discussed to show the design principles. Trade-offs using hybrid doublet or triplet to correct chromatic aberrations are analyzed. In addition, third order aberrations and design freedoms of the DOE and refractive glass thin lenses are compared. For a hybrid design with DOE lens required to be hosted on a flat surface, it is shown that the glass selection for the hosting lens can be used to reduce coma and maintain the same image qualities as the all glass design. Finally, a hybrid 20X 0.5 microscope objective lens is designed and compared with the all refractive optical element design, both approaches achieve similar imaging qualities. It is shown that the hybrid design approach reduces the number of optical elements, other advantages of this design include no high dispersion glasses used and a much more compact optical system.