| 摘要 |
PURPOSE:To stabilize focusing servo by setting the width of the light receiving face of a bisected photodetector so that this width has prescribed relations to the degree of aperture of the light projected to a recording medium and the lateral magnification of the photodetector side to the recording medium side. CONSTITUTION:A width DW of respective light receiving faces of a pair of light detecting elements 21 and 22 constituting a bisected photodetector 20 is set to satisfy 20mum<=DW/M.tan(sin<-1>/NA)<=50mu where NA is the degree of aperture of the light projected to the recording medium and M is the lateral magnification of the photodetector side to the recording medium side. Thus, the frequency responsiveness, the stray light characteristic, and the focusing error signal characteristic are sufficiently secured, and the focusing error signal is not degraded and the quantity of stray light is reduced to improve the frequency responsiveness, and focusing servo is stably performed. |
