| 摘要 |
PURPOSE:To prevent the deterioration of code error ratio characteristic by correcting the deviation of the intermediate frequency due to the fluctuation of mark ratio of a digital signal. CONSTITUTION:A digital signal converted into the intermediate frequency electric signal by a light detection circuit 101 is amplified by an intermediate frequency amplifier circuit 102 provided at the rear stage, band-limited and demodulated by a demodulation circuit 103. One part of the demodulation signal is added to a mark ratio detection circuit 105, resulting in detecting a correction signal according to the mark ratio. The intermediate frequency electric signal is added to a frequency discrimination circuit 104 to detect the deviation from the prescribed value of the intermediate frequency, stabilizing the frequency. As the signal is fluctuated by the mark ratio fluctuation to cause the deviation in the intermediate frequency, the correction signal of the mark ratio detection circuit 105 is added to cancel the fluctuation and to serve as the light frequency control signal for a local oscillation light source 107, stabilizing the intermediate frequency. |
