| 摘要 |
PURPOSE:To hold the frequency of a local oscillation light source at the value right before a break of light input is detected if the light input break is temporarily detected and to put the system back to stable frequency control immediately when a light signal is inputted again regardless of the temporary light input break. CONSTITUTION:When the input signal is temporarily ceased, the output signal of a frequency discriminator 10 also becomes zero, but a timing extracting circuit 14 detects a decrease in the clock component from the base band signal inputted from an input terminal 14a. Consequently, an alarm signal as a light input break signal is inputted from a terminal 14c to the input terminal 15b of a local oscillation light source control circuit 15. The circuit 15 outputs a control signal from an output terminal 15c to a memory 16 and reads ambient temperature and an applied current value corresponding to the frequency value of a local oscillation light source 2 right before the alarm signal is outputted out of a memory 16. Then a control signal which holds the frequency of the local oscillation light source right before the alarm signal is outputted is outputted from a terminal 15d. Consequently, the frequency of the light source 2 is continuously held at the value right before the input break and the control is started when the signal is inputted again. |
