| 摘要 |
<P>PROBLEM TO BE SOLVED: To realize sufficient operational accuracy and operational stability even when using an inexpensive light source of low comparative wavelength stability as a reserve light source for a signal light source, so as to prevent the output of an optical signal from being stopped when switching from an active light source to the reserve light source. <P>SOLUTION: An active light source control circuit 3 monitors the temperature, power, injection current and the like of an active light source 1 and when these values exceeds a predetermined range, it is judged that the light source is in an abnormal state to switch to a reserve light source 2 even while light is normally outputted. At such a time, a frequency divider 10 and a frequency counter 11 are used to regulate an optical frequency of output light of the reserve light source while referring to a beat frequency with the active light source for which the occurrence of abnormality is judged. An appropriate modulating signal is then applied to the reserve light source by a modulating signal changeover switch 13, an output light of the reserve light source and an output light of the active light source are first composed and outputted, and the operation of the light source wherein abnormality occurs is then stopped as needed. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
