Dear Felix,
Thanks for reaching out to us!
Dithering of the laser can be done by directly modulating the applied current to the laser. You can use directly modulated laser for dithering and external modulators for data. This is a very good workaround.
Active signal combiner would include amplifier in it. That can be done by adding electrical or optical amplifier to its input ports depending on the type of combiner. In the passive signal combiner, the passive components are used without the use of external power.
Hope this helps?
Best,
Saurabh Bedi.