| 摘要 |
PURPOSE:To stabilize a feedback loop adaptive to burst signal transmission by comparing a photodetection signal with a reference signal, and holding the bias signal of a semiconductor light emitting element to a specific value or increasing it according to the comparison result. CONSTITUTION:A transmission request signal B is inputted from a terminal 3 to a bias application part 4 and then a burst data signal A is inputted from a terminal 1 to a pulse driving part 2. The application part 4 further inputs the output signal D of a comparator 8. The comparator 8 compares the output of a photodiode PD6 which detects the light output of the semiconductor light emitting element LD5 with the 2nd reference signal corresponding to the threshold value of the LD5 or the 2nd reference signal corresponding to the light output of the LD5 when no thermal sag phenomenon occurs by the signal A. Then a signal L when the photodetection signal of the PD6 is smaller than the reference value or signal H when larger is outputted. The application part 4 operates only when receiving the output L of the comparator 8 to send a bias signal to the LD5, whose light output is increased to prevent a decrease in the light output due to the thermal sag phenomenon; when the H output is received from the comparator 8, the bias is held constant. |
