| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical head device capable of ensuring appropriate diffraction efficiency to rays having respective wavelengths even if using a plurality of light sources having different wavelengths. <P>SOLUTION: The diffraction element 200 has two parallel diffraction gratings 201, 202. The diffraction grating 201 is formed by alternately aligning a nearly rectangular-parallelepiped-shaped optical anisotropic medium having thickness d<SB>1</SB>and an optical isotropic medium, and the product of the difference Δn<SB>1</SB>between normal and abnormal light refractive indexes in the optical anisotropic medium and the thickness d<SB>1</SB>is an integral multiple of λ<SB>2</SB>. In the similarly formed diffraction grating 202, the product of the difference Δn<SB>2</SB>and the thickness d<SB>2</SB>is an integral multiple of λ<SB>1</SB>and the diffraction direction of incident light having wavelengths λ<SB>1</SB>, λ<SB>2</SB>is composed to form an angle ranging from 5 to 85 degrees to a direction having the abnormal light refractive index. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
