Our bi-focal and tri-focal lenses have diffractive pattern etched on the planar side of plano-convex refractive lens (Fig. 1). Collimated plane parallel incident beam gives rise to three main beams: +1st order, zero order (in the case of tri-focal lenses) and -1st order, with focal lengths L1 , L0 and L-1. Our experiments confirmed that the structure of each focal spot is very near to those of refractive lens, except of some reduction of contrast caused by defocused images of other spots.
 

Fig. 1. Optical arrangement for multi-focal lens