| 摘要 |
PURPOSE:To enable an alarm which indicates that a laser diode deteriorates in transmission performance to be given at an optional level by a method wherein a comparator which judges the output signal of an LD drive current detection circuit or an LD drive current limit circuit is provided, and a display circuit through which the LD deterioration warning signal outputted from the comparator is indicated is provided. CONSTITUTION:When an LD deteriorates in optical output due to deterioration, an optical output automatic control device is actuated to increase an LD drive current so as to make the optical output of the LD constant. An LD drive current is increased with deterioration of the LD. An LD drive current detection circuit 5 outputs signals to a comparator 6 corresponding to an LD drive current. When the comparator 6 judges that the inputted signal is larger than a value correspondent to the allowable distortion level upper limit of optical signals, it outputs an LD deterioration warning signal to the display circuit 7. |
