| 摘要 |
PURPOSE:To prevent the occurrence of comatic aberration by using a branching device consisting of a prism which has a square section, two incident surfaces tilted by each prescribed angle to the optical axis of the signal light, and two parallel projecting surfaces set counter to the incident surfaces. CONSTITUTION:A rhombic prism 10 which is different from the conventional one is used as a branching device. This prism 10 consists of a transparent medium which has a rhombic section, two incident surfaces a-b and a-d having the same tilt angle theta to the optical axis of the signal light B, and two projecting surfaces c-b and c-d set counter to the surfaces a-b and a-d respectively. The signal light B1 is refracted at an incident point O1 of the surface a-b, refracted again at a projecting point Q1 of the surface c-d, and projected to a two-split photodetector 13 at a refraction angle +r1. Meanwhile the signal light B2 is refracted at an incident point O2 of the surface a-b, refracted again at a projecting point Q1 of the surface c-b, and projected to the photodetector 13 at a refraction angle +r2. These light B1 and B2 are refracted to be complementarily focuses on the surface c-b and c-d and therefore the same image forming point P is set on the photodetector 13. Thus the comatic aberration is never produced. |
