Patent ID: 8199614
Filing Date: 2012-06-12
Classification: G11B

Abstract:
1. 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 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 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: 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.