A method of optical design of hybrid optical systems by utilization the aplanatic condition is introduced here.
The aplanatic condition was taken as a main optimizing criterion for the design of phase functions of diffractive
optical elements during the optimization procedure. The phase function of the diffractive element can be arbitrary.
We don't restrict ourselves to diffractive optical elements with a spherical phase function. Several hybrid
optical systems, in particular hybrid doublets and hybrid triplets, consisting of one diffractive element and one
or two refractive lenses, were designed and analyzed by this method.