| 摘要 |
PURPOSE:To reduce the number of components and to prevent a crosstalk by integrating a diffraction grating and a holographic grating on a diffraction element and suppressing the transmissivity of a zero order diffraction light in a specific method. CONSTITUTION:For a diffraction element 13, for example, six areas 13a-13f to be mutually divided are integrally formed, and to four areas 13a-13d among them, the holographic gratings are formed, and to the other two areas 13e and 13f, the diffraction gratings are formed. The transmissivity of the zero order diffraction light in the diffraction grating and/or holographic grating positioned in the vicinities of both edges in a direction corresponding to a radial direction B-B' of an optical disk 16 in the diffraction grating 13 is set so as to be smaller than the transmittance of the zero order diffraction light in the diffraction grating and/or holographic grating positioned in the vicinity of a central part in the direction corresponding to the radial direction B-B'. Thus, the number of components is reduced, and simultaneously, the crosstalk is prevented. |
