In order to meet the compatibility between CD

DVD and HD-DVD disc

a single objective lens with a binary diffractive surface and an aspheric surface is designed. The lens is used for three wavelengths which are 780nm

650nm and 405nm

and the numerical apertures are 0.45

0.60 and 0.65

respectively. The binary diffractive surface is divided into two concentric radial zones. According to the harmonic diffraction theory

each region has a different diffraction order depending on the wavelength. The structure and working principle of the three-focus objective lens are presented .The design principle of the aspheric object lens

the parameter of the binary diffractive surface and spherical surface

and the metewand of the aspheric objective lens are described in detail. The use of zemax to simulate the lens is introduced and the simulation results show that the objective lens reaches the practical requirement.