Question

How electrical signal is converted into laser signal?

Answer 1

There are two easy ways to convert electrical signals into optical signals.

The first is to use the electrical signal to modulate the driving current through the laser. My senior project in college involved doing this with an off-the-shelf laser diode. This is easy and cheap to do, but comes with bandwidth limitations (i.e. higher bandwidth needs higher bias power and also induces ringing)

The other way is to use an external optical modulator, which affects the optical power transmission through it. This way is more expensive, but allows for much greater bandwidth with much flatter frequency response and lower needed power.