| 摘要 |
PROBLEM TO BE SOLVED: To surely receive light even when a light source on a transmission side is moved and to provide a desired light converging ratio by attaining a truncated cone shape or a truncated pyramid shape for respectively turning an incident port and an emission port provided with an area smaller than an incident port area to a bottom surface and an upper surface and turning a side face inner side to a light reflection surface. SOLUTION: This light converging device 12 is provided with the incident port 12a and the emission port 12b opened in a square shape and is in the truncated pyramid shape for which they are the bottom surface and the upper surface and the inner surface of the side face 12c is turned to the light reflection surface. Then, the area of the emission port 1.2b is formed smaller than the area of the incident port 12a. Signal light made incident on the light converging device 12 is reflected for plural times by the light reflection surface on the inner side of the side face 12c of the light converging device 12 and converged to a photodetector. Thus, almost all the signal light made incident on the incident port 12a of the light converging device 12 is converged to the photodetector, a light converging magnification (light converging ratio) is substantially improved compared to a conventional case and the light is surely received even when the light source on the transmission side is moved when it is within a prescribed range. |
