| 摘要 |
A first light ray with a wavelength lambd1 emanating from the first emission light source passes through the transparent substrate and is condensed by the objective lens on a signal surface of a first optical disk with a substrate thickness t1, a second light ray with a wavelength lambd2 (<> lambd1) emanating from the second emission light source passes through the transparent substrate and is condensed by the objective lens on a signal surface of a second optical disk with a substrate thickness t2, a step structure of at least one step is formed along a circle or an ellipse on a surface of the transparent substrate, and and by the step of the step structure, a phase of the first light ray is shifted by 2pin1+DELTA1 and a phase of the second light ray is shifted by 2pin2+DELTA2.
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