| 摘要 |
PURPOSE:To make a spot of diffracted light a little larger and make the quantity of movement of the spot relatively small to variation in wavelength, and to enable stable signal detection and increase wavelength variation resistance by giving a distribution to the grating pitch of a diffraction grating. CONSTITUTION:The diffraction grating 26 has the distribution so that the pitch is different with places. Here, K1-K3 are the different grating pitches. When light 23 converged by a lens 22 is made incident on this diffraction grating 26, the diffraction grating 26 differ in angle of diffraction with the places, so the converged spot 27 is a little larger. Therefore, even if the wavelength varies, apparent spot movement is reduced and this diffracted light 24 is photodetected to reproduce a signal, thereby enabling stable reproduction. For the purpose, the diffraction grating 26 is applied to one of a first and second diffraction grating 8, 9 to enable the excellent signal detection wherein the resistance to wavelength variation is increased. |
