| 摘要 |
PURPOSE:To obtain stable output against fluctuations in ambient temperature and/or source voltage by controlling the current of a semiconductor laser according to the peak value and average value of the optical output of the semiconductor laser so that the duty of optical output waveforms is kept constant. CONSTITUTION:An optical transmission circuit consists of a semiconductor laser 1, a drive portion I' and a control portion II' and has a data input terminal (b). The optical output of the semiconductor laser 1 is detected by a photodiode 2 and outputs VP, VA are obtained from respective detected outputs by a peak value detecting circuit 10 and an average value detecting circuit 11, respectively. A bias current control circuit 12 controls a variable current source 9 so that the output VA is equal to the output of a mark rate detecting circuit 15. A threshold control circuit 13 controls the threshold of input data so that when the mark rate of the input data is (m) the output VA is equal to the output m VP of a peak value converting circuit 14. The duty ratio of optical output waveforms is thus kept constant. |
