Usually, the laser diode has a LD to generate laser work on it, but in many precision occasions, the intensity of the light requirements are very strict, such as DVD machines, distance testing equipment, medical equipment, testing instruments and so on, the work of these products, the light is too strong or too weak will affect the accuracy of the data, and the intensity of the light of the LD in the case of constant-current will be with the rise in temperature and decrease, will also gradually decrease with the increase in use time, so to PD feedback. The light intensity of the LD will decrease with the increase of temperature under constant current, and will also decrease gradually with the increase of using time, so we should use the signal of PD feedback to adjust the light intensity automatically to reach a constant value needed.
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