| 摘要 |
PURPOSE:To obtain a focusing error detector with superior stability for temperature by setting the center point of a line segment connecting a first convergent point to a second convergent point on an optical detector, the light emitting point of a semiconductor laser, and the center of a reflection type hologram optical device so as to aligned on the same plane. CONSTITUTION:The intersection of an optical axis with the parting straight line of a reflection type grating optical device, the first and second convergent points, and the light emitting point of a light source are arranged so as to be aligned on the same plane. The reflection type hologram optical device 27 exists on a plane X-Y, and a rectangular coordinate system setting an axis perpendicular to the plane X-Y as an axis Z is assumed, and the light emitting point 14 of the semiconductor laser is set as (xg, yg, zg) and the position 15 of the convergent point of a light beam on the optical detector as (xf, yf, zf). At such a case, an interference fringe on which the hologram optical device is recorded is generated by a divergent spherical wave by those two points, and its transfer function is supplied as equation I. In equation I, lambda1 represents the design wavelength of the reflection type hologram optical device, and corresponds to oscillation wavelength under the room temperature of the semiconductor laser generally. In such a way, it is possible to obtain the focusing error detector having stable error detecting characteristic against the fluctuation of the wavelength of a light source. |
