Patent Number: 6,434,104

Title: Objective lens, optical pickup device and optical disk device

Abstract: An objective lens comprises a single objective lens adapted to a finitesystem having first and second aspherical surfaces and a hologram isformed on at least one of said aspherical surfaces. The light of thepositive 1st order or that of the negative 1st order of the hologram issubjected to optimal correction of spherical aberration under actualoperating conditions. When a semiconductor laser is used as light source,the change in the spherical aberration caused by the change in therefractive index arising as a result of the change in the environmentaltemperature of the medium between the first surface and the second surfaceis substantially offset by the change in the spherical aberration of thehologram attributable to the change in the oscillation wavelength of thesemiconductor laser of the light source caused by the change in theenvironmental temperature so that, if the objective lens has a numericalaperture greater than 0.5, the astigmatism is favorably correctedregardless of the change in the environment particularly in terms oftemperature. Such an objective lens can make it easy to downsize anoptical pickup device comprising it.

Inventors: Asoma; Yoshito (Saitama, JP)


International Classification: G11B 7/135 (20060101); G11B 7/125 (20060101); G11B 007/00 ()

Expiration Date: 08/13/2014