Condenser with first and second photodetectors with three sections each and having focal points before and after the surface of detectors

摘要

To provide a light receiving device, a light detecting device, and an optical signal reproducing device each of which allows one to perform many different computations in detecting aberration amounts and focus error quantities without requiring exact position relations between laser light to be received and light receiving elements, and between the light receiving elements. First and second light receiving elements 43 ₊ and 43 _- are used which receive condensed light at positions equidistantly spaced from an focal point X before and after the light images, respectively.