| 摘要 |
PURPOSE:To improve the wavefront aberration of a primary diffracted light by forming the approximately center part of a recessed or projection part of a phase groove of a diffraction grating provided to an optical reproducing device so that a prescribed relative formula is satisfied. CONSTITUTION:A laser beam 2 from a light source 1 is diffracted by a diffraction grating 3 and a zero-th order beam 4b and + or -1-st order beams 4a and 4c are converged on an optical disk 6 via an objective lens 5. These reflected beams travel back and are made incident on a photodetector 9 via the grating 3 and a concaved lens 8. The grating 3 satisfies another equation in an x-y coordinate system as shown in the figure. Here beta shows the lateral magnification of the lens 5 together with S showing the space between 0-th order and a primary light spots on a recording medium, L showing an optical distance between the grating 3 and the source 1, (a) showing an angle formed by a straight line connecting light spots between zero-th order and + or -1-st order diffracted beams and the direction of an (x) axis, (b) showing an angle formed between the surface of the grating 3 and the optical axis of an incident light beam, showing the wavelength of the laser beam, and (m) showing an optional integer respectively. |
