AUTOMATIC STABILIZATION FOR EMITTED LIGHT POWER OF SEMICONDUCTOR LASER

PURPOSE:To automatically stabilize the emitted light power of a semiconductor laser by a method wherein photo output is monitored, the threshold value of the photo output is detected according to the magnitude of the amount of variation of the photo output to the amount of variation of a bias current and the bias current is controlled in such a way that the current is always held in the vicinity of the threshold value or right under the threshold value. CONSTITUTION:Reference photo output (Pr) and the range (DELTA) of an allowble error are given in advance and when photo output is larger than the reference photo output, a frag (Frg) is displayed as 1 and when the photo output is smaller than the reference photo output, the frag is put as -1. Then, a bias current is reduced by FrgXDELTAIb. Whether the amount DELTAP of differential variation of light at this time is suddenly changed more than a reference value (DELTAPr) is judged. If the amount does not exceed the reference value, the bias current is not changed exceeding its threshold value. Therefore, the bias current is changed until exceeding the threshold value. When the bias current is wanted to set right under the threshold value, the value of the frag is checked up at a point, when the bias current exceeds the threshold value, and in case bias is decreased, an exist from the loop takes place unconditionally. However, in case the bias is increased, this is decreased by DELTAIb to return right under the threshold value.