Popular Post JohnSwenson Posted August 19, 2020 Popular Post Share Posted August 19, 2020 I think I might be able to explain a little bit about what is going on here with modulating lasers and the "current injection". Solid state lasers have two primary modes they operate in, coherent and non-coherent. (LED mode). At lower currents they are expensive LEDs. At currents above a certain threshold they are a laser. (the "threshold of course is not a "point", it is a small range, inside that range weird things happen). The modulation takes advantage of this, it is not turning the laser "on and off", zero current and full current. The "off" state is a current a little below the threshold and the "on" state is a little above. Thus the light beam is not turning completely on and off, it is changing from non-coherent to coherent. After the laser is some form of optical system that lets a lot of light through if it is coherent and not much if it is non-coherent. Don't ask me WHAT that optical component is, I have no idea. Of course the actual current value of the threshold varies with temperature, which means you need some sort of servo system tracking the threshold. The simple matter of engineering. So the laser system is being modulated by a fairly small current change. Its not zero, but the change is a lot less than the full current needed to make the laser lase. This temperature dependence is one of the reasons optical protocols are such that the average amount of time in "on" and "off" are fairly constant so the temperature is not flailing around with the data. John S. kennyb123, Superdad and OAudio 3 Link to comment
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