Self-Heterodyne Linewidth Measurement

Dear All,

The structure of a self-heterodyne linewidth measurement setup is described in fig1. The AOM (Acoutso-Optic Modulator) acts as a frequency shifter. So the problem is that there is no such component in the interconnect to shift the frequency of the laser in the first arm of the setup. A 40MHz shift would be enough in my case.
Is there any suggestion? or more generally Is there any suggestion to build a setup for self-heterodyne linewidth measurement?
FYI: In this link Homodyne Linewidth Measurement is described.

fig1:

Thanks in advance for your help.
Sincerely,
Emad

Hello @Emad,

Thank you for the question. Sorry for the late reply, I had to discuss this with a colleague.

You can create a frequency shifter using the scripted electrical source and scripted optical modulator elements. Using these elements, you can apply a phase shift that is linear in time to the signal, shifting the frequency. Here is an example:

You can change the frequency shift by adjusting the constant in the electrical source script (in the screenshot above, this constant is 1e9).

Here is the example file: laser_freq_shift.icp (169.1 KB)

I hope this helps. Let me know if you have any questions.

1 Like

Hello @kjohnson,
Many thanks for your help.

I also tried freq. shifting based on an MZI. It will shift the laser freq (193.1THz) by a 4GHz. Here you can see the circuit.
image
And this is the result (Blue: Optical signal after MZI, Green: Optical Signal after an optical rect-filter)
image

Thanks again for your support.
Stay safe.
Sincerely,
Emad

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