| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical head which receives three kinds of light different in wavelength, depending on a layout of a light receiving area of a single photodetector. <P>SOLUTION: A wavelength selection diffraction element 10a is disposed only in a return optical path of light of a wavelength λ<SB>1</SB>in a wavelength band of 405 nm, light of a wavelength λ<SB>2</SB>in a wavelength band of 660nm, and light of a wavelength λ<SB>3</SB>in a wavelength band of785 nm, all of which are reflected in the same way on an optical disk. The wavelength selection diffraction element 10a has: a wavelength plate 12 which converts the light of wavelength λ<SB>1</SB>and the light of wavelength λ<SB>2</SB>into perpendicular linear polarized light, a first diffraction grating 13 to diffract the light of wavelength λ<SB>1</SB>but to allow the light of wavelength λ<SB>2</SB>to pass without diffracting, and a second diffraction grating 15 to allow the light of wavelength λ<SB>2</SB>to pass without diffracting while diffracting the light of wavelength λ<SB>1.</SB>The optical head, which is allowed to design each wavelength light receiving area of the photodetector with high degree of freedom, is obtained by using 0th diffraction efficiency high on the light of wavelength λ<SB>3</SB>and independently adjusting diffraction efficiency and a diffraction angle of each wavelength light. <P>COPYRIGHT: (C)2011,JPO&INPIT |
