| 摘要 |
PURPOSE:To prevent the deterioration of a C/N due to the decrease of the number of channels for a light transmission. CONSTITUTION:At a transmission side, a level adjustment is executed so that the means level over the entire transmission band of a frequency multiplexed electric signal which is a modulated signal can be turned to a prescribed level, a laser beam is amplitude-modulated, and the obtained frequency multiplexed optical signal is transmitted to an optical transmission line, At a reception side, the optical signal is converted into an electric signal by a PIN photodiode 28, and amplified by amplifiers 21 and 23. The level of the pilot signal of a prescribed frequency among the signals outputted by the amplifier 23 is detected, compared with a prescribed level, and the level adjustment is executed by a PIN diode variable attanuator according to the deviation. Therefore, the signal level of the channel of the frequency division multiplexed electric signal transmitted to an electric transmission line is made constant even when the increase or correction of the modulation level is executed at the transmission side, and the deterioration of the C/N due to the decrease of the using channels can be prevented. |
