Laser Modulation: Why Do We Need Bias and Modulation Currents?

[fuyejun]

Hi:


I confused about the follow things, why people say a laser has bias current and modulation current. why a laser has modulation current?

 

[berkeman]

Hi:


I confused about the follow things, why people say a laser has bias current and modulation current. why a laser has modulation current?

If you mean in the context of a laser diode, you need to turn it on (with some DC bias current), before you can modulate it (say, amplitude modulate it to some modulation depth) with information.

Modulation depth or "index": http://en.wikipedia.org/wiki/Amplitude_modulation#Modulation_index

.

 

[sophiecentaur]

There is more to modulating a laser than just 'turning it on and off' if you want to get the best result (i.e. producing a good data pulse shape). It is, essentially, a pretty non-linear device and I think the bias current is just a contribution towards providing it with a suitable driving waveform to produce a reasonably shaped modulation 'envelope'.

 

[fuyejun]

I read it from a book, there 2 kind of modulation, direct modulation and external modulation,


so I think when use direct modulation such 2 currents should be concerned ,bcs, it add "ONE" at "ZERO" current.

In external modulation, laser act as a CW (continuous wave) so there is no Modulation current.

But, above issues is what I think about,If there are wrong pls,tell me. Thanks a lot .