The incentive method of
laser drivers is mostly injection current form. When the injection current is greater than the threshold current, radiation power will rapidly rise with the increase of the current. Therefore, by changing the injection current, the output optical power can be adjusted. In order to control semiconductor laser, the methods of automatic control are usually adopted, which includes constant current/power/voltage control.
In the constant power control mode, by using photoelectric detector, a small portion of laser power can be received and transformed into monitor current. Then after the monitor current is through the current to voltage convertor, a closed loop negative feedback control will be formed by comparing feedback network of constant power control with a set value. Due to the influences of temperature or other factors, the laser output power will change, and the negative feedback can control the optical power to keep stable.
In a special situation, constant voltage control is very simple and useful. When the drive voltage is constant as demanded, this mode will be selected.
In the constant current control mode, by current sampling and feedback, the current driving unit is provided active control and can make the current drift minimum. When cooperating with
temperature control, the using effect will become better.
Now constant current control is usually adopted because semiconductor laser devices commonly use constant current source.
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