| 摘要 |
PURPOSE:To eliminate influence due to the wavelength dispersion of an optical fiber by detecting the beat signal of two optical signals by synthesizing the optical signal sent from a transmitter and the optical signal of a semiconductor laser for local oscillation, and performing demodulation by extracting a specific frequency component from the signal. CONSTITUTION:The optical signal transmitted to a receiver 200 is made incident on a photocoupler 3, and the optical signal of the semiconductor laser 2 for local oscillation is synthesized with the optical signal from the transmitter 100, and is inputted to a light reception circuit 20. At the circuit, the beat signal of the two optical signals is detected. The signal is inputted to a band-pass filter 21 which passes only a component with frequency f1, and is inputted to a demodulation circuit 22, then, is smoothed. The demodulation can be performed even when the optical frequency of the optical signal from the transmitter or that of the optical signal of the semiconductor laser for local oscillation is fluctuated to some extent, and also, the influence due to the dispersion of the optical fiber can be eliminated. |
