A laser driver with an external Bias-Tee for modulation

Thread Starter


Joined Aug 31, 2018
Hello members,

As the title says, I would like to add an external Bias tee to modulate a high frequency signal into a laserdiode, because the laser driver I have chosen does not have a built-in modulation circuit. I have bought the MLD203P1 laserdiode driver from thorlabs. This laser driver does not have the modulation circuit, so I decided to add an external bias-tee to it. The typical application of the MLD203P1 is seen below.


What I so far know is that a bias tee consist of an inductor and a capacitor, which is in parallel and with one DC-input, one AC-input and one AC+DC output. So I think this should be the solution. This is seen below.


I just only need a modulation range of 10 kHz to 20 MHz. I have also read the datasheet of the MLD203P1 and don't see a problem if I attach the external bias to the LDA (Laser diode Anode).

So I wonder if this is working or has anyone tried it with another laserdriver? And is this the right path I am walking on to get a modulation signal of the laserdiode?

Datasheet of MLD2031P1: https://www.thorlabs.com/drawings/8c0acf99c70bcbeb-392580F3-E400-B9B9-C9E56C95CCB14E62/MLD203P1-DataSheet.pdf

Best regards,



Joined Jun 17, 2014
Just a note...

You have to be careful when doing something like this because the diode could blow out if it gets too much current. The chips usually regulate that.