| 摘要 |
PURPOSE:To stabilize optical scanning for a long time in consideration of secular change by setting a temperature shifted from the temperature, at which the time difference between outputs of two photodetectors exceeds a set value, by a prescribed value. CONSTITUTION:While actual scanning is not performed, a CPU56 operates a counter 58 to count clock pulses of an oscillator 60, and a signal output is raised stepwise from a prescribed initial value each time when a prescribed number of pulses are counted. Meanwhile, outputs of photodetectors 34 and 36 are supplied to an FF50 to obtain a signal corresponding to the time difference between these outputs, and this signal is counted in a counter 52 by clock pulses of the oscillator 60, and the counted output is converted by a D/A converter 53 and is applied to a comparator 54. When the comparator 54 is so constituted that the output is issued when the input level becomes lower than the comparison level, the temperature of a semiconductor laser 10 is controlled to a value near the center part of a shelf-shaped part if the set temperature for temperature control shifted from the temperature for output generation to the lower temperature side by a prescribed value is set. |
