| 摘要 |
PURPOSE:To miniaturize and to lighten a device by detecting a focusing error signal and a tracking error signal with a hologram element in which different diffraction grating or a non-hologram area is formed in its one part. CONSTITUTION:A hologram element 6 can reproduce a wave front to have a pair or two pairs of conjugate focuses and forms an area, a non-hologram, etc., in which a simple grating pattern is recorded in its one part in a different direction from others respectively, and different diffraction grating. For a beam emitted from a light source 1, zero-th order diffracted light is converged to a disk 4 on going, and after it made as parallel light on returning, it is made incident on the element 6. then, beside the zero-th order diffracted light, wave fronts 71-76 to have a pair of conjugate focuses outside an axis are formed. A focusing error signal is obtained from the wave fronts 71 and 72, a tracking signal is obtained from the wave fronts 73-76. Thus, even when wavelength fluctuation is generated to the light source, the stable signal is always detected with the fixed diffracted light, and a device can be miniaturized and be lightened. |
