| 摘要 |
PROBLEM TO BE SOLVED: To provide an objective lens requiring severe temperature characteristics which makes possible recording and reproduction to optical information recording media whose transparent substrates are different in thickness by providing the objective lens with different optical functions while keeping the temperature characteristics. SOLUTION: The objective lens is formed with homogeneous optical materials. A refractive index variation represented by dn/dT to a variation in the temperature of the optical materials satisfies the equation |dn/dT|<=10.0×10<-6> (/ deg.C) at the wavelength of a light source at the room temperature. The objective lens is formed so that different optical actions may be given to each of at least two optical functions arranged in the direction crossing an optical axis, and uses at least a luminous flux passing through the optical function on the exterior side only for the recording and reproduction to a first information recording medium. The objective lens is provided with a diffraction structure. |
