| 摘要 |
PURPOSE:To stabilize the receiving level, and to improve the transmission quality, by installing an amplitude transmission type space filter for shaping an intensity distribution of a transmitting light, in an optical path of a light wave emitted from a transmitter. CONSTITUTION:As for a laser beam emitted from a semiconductor laser 25 of a transmitter 2, the intensity distribution of its light is reduced smoothly extending from the center of a transmission lens 24 to the peripheral part of the opening by an amplitude transmission type space filter 26, and said light transmits through the lens 24 and transmitted through the space. Its light passes through a BPF 51 and a receiving lens 52 of a receiving device 5 and made incident on a photodetector 53, and its output signal is sent to a receiving circuit 54. The transmittivity T of the filter 26 is given by the expression. In this regard, F, and ZF, and (x), (y), and DF denote an F-number of the transmitting lens 24, a distance between a light source 25 and the filter 26, orthogonal coordinate axes whose origin is an intersection (the center of the lens 24) of the lens 24 and the optical axis taken on the surface of the filter 26, respectively, and the opening luminous flux diameter of the lens 24, respectively. |
