| 摘要 |
PURPOSE:To evade disabled communication even if a direction of a received optical axis is deviated when a communication enable limit distance in a near distance is decreased by arranging plural photodetection optical systems with a wide direction angle around the transmission optical system so as to widen the light reception width and the permissible range of the beam incident direction. CONSTITUTION:Since lots of photodetection optical systems with a wide direction angle are arranged around the transmission optical axis, the reception width W of a mobile station 2 is widened. Even if the transmission optical beam 6a of a fixed station 1 is made thin, a large axis deviation permissible width is obtained and a distance of access limit not causing deviation of optical axis due to the deviation of axis at a near distance is decreased and the beam incident direction able to be coupled to a photodetector 11 is widened. Thus, even if the direction angle at the side of a fixed station 1 is decreased, the communication enable limit distance at a near distance is decreased and disabled communication even with the deviation of the photodetection optical axis at the mobile station 2, disabled communication is prevented. |
