Patent ID: 8199614

Claim:
An aberration correction element comprising: a diffraction plane configured to correct a spherical aberration caused by a difference among a first optical recording medium, a second optical recording medium, and a third recording medium by transmitting first beams of light having a wavelength of λ 1 emitted from a first light source to read and write data on the first recording medium comprising a substrate having a thickness of t 1 , and diffracting second beams of light having a wavelength of λ 2 emitted from a second light source to read and write data on the second recording medium comprising a substrate having a thickness of t 2 , and third beams of light having a wavelength of λ 3 emitted from a third light source to read and write data on the third recording medium comprising a substrate having a thickness of t 3 ; and a phase shifter plane comprising a step form having multiple steps along an optical axis direction that is formed in a ring band manner with a step height of a significant multiple integral of each of wavelengths of λ 1 , λ 2 , and λ 3 at room temperature, the phase shifter plane generating a spherical aberration −ΔSA having a reverse direction to a spherical aberration ΔSA generated at an objective lens optimized for the first optical recording medium according to a temperature change, wherein in the phase shifter plane, thickness of the step form in the optical axis direction becomes smaller in a radial direction from the optical axis toward an outer portion of the phase shifter plane to a first radial position that is a predetermined distance away from the optical axis, and then becomes greater from the first radial position to the outer portion of the phase shifter plane, and wherein the aberration correction element is formed of resin material and configured to satisfy the following relationships 1 and 2: ( dn/dT )×( dh/dT )× m=Δx Relationship 1 −3.6×10 −10 mm/° C. 2 ≦Δx≦− 2.1×10 −10 mm/° C. 2 Relationship 2 where dn/dT has units of [1/° C.] and represents a change in a refraction factor of the resin material based on 1° C., dh/dT has units of [mm/° C.] and represents a change in the step height based on 1° C., m represents a number of the multiple steps and an integer greater than 1, and Δx has units of [mm/° C. 2 ] and represents a value obtained by the relationship 1.