| 摘要 |
PROBLEM TO BE SOLVED: To control an optical output to be constant without deteriorating an extinction ratio of the optical output, when the differential quantum efficiency and the threshold current of an LD deteriorate. SOLUTION: An LD drive section 2 supplies a drive current, in response to input data to an LD 3. A monitor section 4 monitors an optical output of the LD, and an APC circuit 5 controls the drive current in response to a monitored average voltage 51. A consecutive 0 detector 10 activates a level comparator control switch 12, when receiving consecutive 0 data in excess of a prescribed length to operate a level comparator 11, where an optical monitor voltage 41 is compared with a reference voltage. When an optical output with respect to data '0' exceeds a reference value, an extinction ratio deterioration signal 111 is generated and a data control section 13 increases the drive current 21 to increase the optical output, and then the voltage 51 is increased. The APC circuit 6 decreases the LD bias current, by using the voltage 51 for a reference to obtain the optical output with less extinction ratio deterioration and waveform distortion. |
