| 摘要 |
PURPOSE: To enhance the safety and the detection sensitivity with reference to a change in a wavelength of a light-emitting means, to miniaturize a device and to increase the safety of the start of a servo operation in the device by which light from the light-emitting means is image-formed in an image formation means and by which a focus error is detected on the basis of its reflected light. CONSTITUTION: Light which is emitted from a laser diode 101 and which is condensed on an optical disk 106 as an image formation object by a lens 105 is reflected by a polarization beam splitter 103, and it is branched into two luminous fluxes by a transmission reflecting plate 1 while it is being condensed by a lens 107. Spots by the respective luminous fluxes are formed to be fan shapes whose foci have been made to agree, the spots are received and operated in a state that they are stretched between adjacent light-receiving regions in photodiodes 3, 4, and a focus detection error is detected. |
