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.
Thanks in advance for your help.