| 摘要 |
PURPOSE:To facilitate the manufacture of a diffracting means and to attain thin profile and low cost by providing a reflecting type diffracting element represented by a special forming formula. CONSTITUTION:Let the optical length from a light source 1 generating a light of wavelength lambda be L1(x, y) and let the optical length of a conjugation point of the light source be L2(x, y), the reflection type diffracting element 11 expressed as a shape formula of L1(x, y)-L2(x, y)=mlambda is provided (where m=0, + or -1, + or -2, ...). One diffracting light diffracted and reflected by the diffracting means 11 is irradiated onto a disc 4 via an objective lens 3 and the other diffracted light diffracted and reflected by the diffracting means 11 is received by a photodetector 5. Thus, the depth of the groove of the diffracting means is made shallower more than that of the transmission type. Thus, the manufacture of the diffracting means is facilitated and thin profile and low cost are realized. |
