| 摘要 |
PURPOSE:To obtain the best light receiving power density at all times at the reception side regardless of the transmission distance by varying the emitting beam diameter for the transmission object according to the distance between the measured object to be transmitted. CONSTITUTION:A distance measurement circuit 90 of an optical space transmitter 10 at the transmission side calculates the device-to-device distance (d) based on the delay time (t) required to return a pulse for transmission distance measurement being reflected on the corner cubprism of the transmitter 10 and the light speed (c) by d=c.t/2. Thus, the circuit 90 which measures the distance from the device 10 generates the driving control information of a voice coil motor 92 according to the measured distance. Then the information is sent to a voice coil motor driving circuit 91. The circuit 91 generates the driving signal of the voice coil motor 92 based on the driving control information. When the measurement distance is short, a lens 38 is approached in the direction separated from a laser diode 36 of the lens 38 in the direction enlarging the light emitting beam diameter or in the direction reducing the beam diameter. |
