DESIGN OF DIFFRACTIVE PHASE ELEMENTS THAT REALIZE AXIAL-INTENSITY MODULATION BASED ON THE CONJUGATE-GRADIENT METHOD

We employ the conjugate-gradient method to design diffractive phase el ements (DPE's) that implement the predefined axial-intensity modulatio n over a given axial region. We introduce an error function for guidin g the design of DPE's and for evaluating their performance. Numerical simulations are carried out for several examples, for instance, the de sign of the DPE that generates four foci with equal or unequal spacing between the consecutive foci along the optical axis and the DPE that produces a sinusoidlike axial-intensity modulation. The obtained resul ts show that the designed DPE's can satisfactorily match practical req uirements. (C) 1998 Optical Society of America.