| 摘要 |
PURPOSE:To reduce noise without decreasing transmitting signals and receiving signals by arranging an optical fiber at a position distant rather than the focal position of a second lens, arranging an LED at a position closer than the focal position of a first lens and reducing the inner diameter of a diaphragm. CONSTITUTION:An optical fiber 11 and a lens 4 are arranged so that a distance L between them can be L>Fb. The Fb is the back focus of the lens 4. Light emitted from the optical fiber 11 is converged by the lens 4 and arrives at a photodetector PD2 after reflecting the almost half quantity of the light on a polarized beam splitter 5. On the other hand, a diaphragm 8 shields the most of light reflected on the end face, etc., of the optical fiber 11 after being emitted from an LED 1. Thus, the noise is considerably reduced without decreasing the receiving signals. |
