| 摘要 |
PURPOSE:To prevent deterioration and breakdown of a semiconductor laser even if a control system of drive circuit becomes off by providing a photodetector which receives light emitted from a semiconductor laser and provides an output of signal depending on the received light and biasing a current flowing through the semiconductor laser when output signal of photodetector goes out of the predetermined value. CONSTITUTION:In case the system of semiconductor laser drive circuit becomes off and the signal from the photodiode 6 is no longer input to a drive amplifier 7, it increases a current to flow into a laser chip 1a in view of increasing amount of light of semiconductor laser 1, judging that a signal from the photodiode 6 is low for the voltage of reference voltage input terminal 8. In this case, a photocurrent obtained from the photodiode 9 provided in the semiconductor laser 1 is converted to a voltage with the resistors 21, 22 or the terminal voltage of resistor 22 turns on a transistor 23. Thereby, a current flowing into the laser chip 1a is biased to the transistor 23, thereby lessening amount of light of laser chip 1a and preventing deterioration and breakdown semiconductor laser. |
