| 摘要 |
<P>PROBLEM TO BE SOLVED: To correct spherical aberration caused by difference of thickness of substrates of first and second optical recording mediums with a phase optical element. <P>SOLUTION: The phase optical element 20 is characterized in that, when a wavelength having the same value as the reference wavelength λ1 of a first laser beam L1 is set as a design wavelength λ, an inner periphery-side stairway shaped phase difference pattern part 20a1 is formed in zone shape of plurality of steps, each of which has height equivalent to a phase difference being a roughly 1λ in an inner peripheral area and also an outer periphery-side flatness part 20a2 is formed in flatness with height of the middle height of a position of the lowest stairway and a position of the highest stairway of the inner periphery-side stairway shaped phase difference pattern part 20a1 and also with height equivalent to phase differences of roughly an integral multiple of the design wavelength λ to the position of the lowest stairway in an outer peripheral area connected to the inner periphery-side stairway shaped phase difference pattern part 20a1. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
