| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical system for optical pickup device, eliminates the influence of temperature variation by arranging a plastic coupling lens only in the optical path of a going optical system and satisfying the quantity of deviation of an optical detector position from the original image point of a return optical system even in case of the temperature variation and a coupling lens, and an optical information recording and reproducing device which. SOLUTION: This optical system for optical pickup device comprises an objective 4 and the plastic coupling lens 2 which converts the angle of a spread of luminous flux from a light source 1, and the luminous flux from the light source passes through the objective and coupling lens when an image is formed on an optical information recording medium 10 and the reflected light from the optical information recording medium does not pass through the coupling lens and passes through the objective when detected by an optical detector 12; and a ring-shaped diffraction structure is formed on at least one surface 2a of the coupling lens to generate an under spherical aberration when long-wavelength light is made incident and the coupling lens has positive refracting power on the whole. |
