| 摘要 |
PROBLEM TO BE SOLVED: To realize complementary focus error detection by making nearly coincident two positions wherein the ±1st order diffracted light beams by a first diffraction area of light having a first wavelength make incident on a light receiving element substrate, with two positions wherein the ±1st order diffracted light beams by a second diffraction area of the light having a second wavelength make incident on the light receiving element substrate. SOLUTION: A first position P1 and a second position P1' wherein the ±1st order diffracted light beams b1, b1' of light having a first wavelength λ1 by a first diffraction area 11 make incident on a light receiving element substrate 15 respectively nearly mutually coincide with the first position P1 and the second position P1' wherein the ±1st order diffracted light beams b4, b4' of the light having a second wavelength λ2 by a second diffraction area 13 make incident on the light receiving element substrate 15. Therefore, with respect to two wavelengths λ1, λ2, a focus error signal by a complementary spot size method is calculated based on an output from a pair of optical detecting diodes in the positions P1, P1' proximate to a conjugate point C. |
