| 摘要 |
<P>PROBLEM TO BE SOLVED: To solve problems in which efficiency in light usability for a CD system is not ensured, the number of optical parts is large, manufacturing precision for the optical parts is severe, and working distance is extremely shortened. <P>SOLUTION: When the numerical aperture numbers of object lens for beams of wavelengths from a light source λ1, λ2, λ3 are NA1, NA2, NA3, respectively, and thickness of each of the light transmittance layers for the optical recording medium for performing record reproducing with the beams of each of the wavelengths of λ1, λ2, λ3 are t1, t2, t3, respectively, NA1≈NA2>NA3, and t1=t2<t3. <P>COPYRIGHT: (C)2004,JPO |
