I have some problems on understanding how this circuit works. Its aim is that of:
- bias correctly the LASER diode at left
- send a signal (DATA) to the LASER diode
- stabilize the working point of the LASER diode through the feedback system at right
My doubt is about the feedback system at right. I'd say that it will be useful if:
- when the light power is too high, the photodetector makes the bias current of the LASER reduce;
- when the light power is too low, the photodetector makes the bias current of the LASER increase;
But this schematic confuses me (also because GND and VCC have are taken in a different way). Suppose the light emitted power is too high: the photodetector (a photodiode, I suppose) is flown by a higher current from GND to -5.2V. What does this current cause to the operational amplifier? It is an inverting op amp but I do not know how it works in this case, since I do not know if the current provided by the photodetector goes towards the amplifier output through the feedback, or if it goes towards the resistor where it is written VDC.