| 摘要 |
PURPOSE:To minimize the deviation of an optical path due to thermal influences so as to reduce the variation of output signals, by forming the 2nd light splitting means composed of a half prism in one body with the 1st light splitting means composed of a polarizing and reflecting prism and separating information signals from focussing signals. CONSTITUTION:A polarizing and reflecting prism 3 is constituted by combining a rectangular prism and parallelogrammatic prism in one body and arranged in such a way that, at the initial state, an incident ray is perpendicularly introduced to the prism 3' and reflected at a right angle by a reflecting surface 3a of the prism 3'. The reflected ray is again reflected at right angles by another reflecting surface 3e and goes out from the prism 3' perpendicularly to the prism 3'. When the prism 3' is deviated counterclockwise by, for example, DELTAtheta against the optical axis due to thermal influences, the optical axis of incidence is bent counterclockwise by DELTAtheta-sin<-1>(sinDELTAtheta/n) at the plane of incidence 3f, by DELTAtheta+sin<-1>(sinDELTAtheta/n) at the reflecting surface 3g, and by DELTAtheta-sin<-1>(sin DELTAtheta/ n) at the reflecting surface 3h and coincides with the initial outgoing optical axis at the plane 3i of outgoing. Therefore, almost all of the thermal influences are eliminated. |
