| 摘要 |
PURPOSE:To facilitate working and to reduce the cost, by making a unidirectional converging beam, which is converged in the direction of the radius of a plane disc and has the convergence line near its grating, incident to a fixed position of this disc. CONSTITUTION:The reproducing illumination light made incident to a fixed position of a disc 2 of an optical scanning device from below is converged in one direction by a cylindrical lens 3 and becomes beams which are a parallel light in the circumferential direction of the disc and are converged on the disc surface in the direction of the radius. The 0-order light from a hologram goes straight as it is, and the diffraction light is diffracted at an exit angle theta=sin<-1> (lambda/D) (lambda is the wavelength of the illumination light, and D is pitches of the grating). In this case, since the hologram diffraction point and the scanning point are conjugate, the light is converged to the same point independently of the exit angle, and the scanning line is one straight line regardless of the conical movement of the diffraction light. Consequently, the deviation of the scanning line is reduced considerably, and the cost is reduced. |
