| 摘要 |
PROBLEM TO BE SOLVED: To transmit a control signal while multiplexing the control signal and the main signal on one signal beam by providing a transmitting means for the signal beam whose light intensity is modulated by the main signal and whose optical frequency is modulated by the control signal, and a receiving means for extracting the control signal by detecting the frequency deviation of the signal beam. SOLUTION: When the modulation current width is small, a semiconductor laser 11 mainly performs frequency modulation without changing light intensity so much. On the side of transmission, a signal beam FM is provided by utilizing such a character and further, a signal beam FM+IM intensity-modulated by a light intensity modulator 12 is provided. On the side of reception, branched transmission light is further bisected by a beam splitter. The intensity of the light to be inputted to one optical filter is defined as Pin and characteristics are selected so that the frequency deviation of the signal beam can be converted to light intensity by a transmission factor t(f) of the filter. The output signal of photodetector is expressed as k1 .Pin.T(f) and an output is expressed as k2 .Pin. In this case, k1 and k2 are proportion constants. At a division circuit, Pin is erased and a value based on only the optical frequency, namely, only the control signal is extracted. |
