| 摘要 |
PURPOSE:To monitor the analog modulation distortion level of a light emitting element under the line operating state, by superimposing a pilot signal to an analog electric signal, in an optical communication system where the light emitting element is appplied with intensity modulation by the analog electric signal. CONSTITUTION:An output of an analog electric signal source 11 is coupled with an output of a pilot signal source 12 with a coupler 13 and amplified at an amplifier 14. The light emitting element 15 outputs an optical output modulated for the intensity with an output signal of the amplifier 14 and transmits it from an optical output terminal 111 to a transmission line. On the other hand, a part of the optical output of the light emitting element 15 is monitored at a photodetector 16 and amplified at an amplifier 17. The frequency component, e.g., twice that of the pilot signal is extracted from the output of the amplifier 17 at a band pass filber 18 as the modulation distortion component. The output of the band pass filter 18 is rectified at a rectifier circuit 19 and the change in the distorted wave level is monitored at a discriminating circuit 110. The pilot signal is superimposed on the analog electric signal in this way to modulate the intensity of the light emitting element, a part of the output light of the light emitting element 15 is received and converted into an electric signal, the distorted component is extracted at the band pass filter 18 to monitor the level, allowing to detect the deterioration in the linearity of the light emitting element 15 even during the operation of line, and the deterioration in the modulation distortion characteristic based on it. |
