US Patent 7327662 Optical pickup and optical disk drive

A diffraction element is interposed between a semiconductor laser and collimator lens. Other diffracted light than zero-order light output from the diffraction element will not be focused on an optical recording medium and the amount of light condensed to the focus of the zero-order light is thus smaller. The diffraction element is variable in diffraction efficiency. When the diffraction efficiency of the diffraction element is raised, an optical pickup device will utilize the light with a lower efficiency. With the diffraction efficiency being lowered, the optical pickup device will utilize the light with a higher efficiency. Thus, the optical pickup device can utilize the light with a variable efficiency without having to being designed larger.