I’d like to create a self-homodyne linewidth measurement setup by using a delay line to prevent any coherence effects between the two signals. I created the below circuit, where a CW input with 10 MHz linewidth is split into two. One arm is passed through a 10 km long lossless fiber. The beat note is then read with a photodetector and a spectrum analyzer. However, it seems like the system isn’t responding the way I’d expect.
- First of all, are there any coherence effects in INTERCONNECT to begin with? Can I expect to see anything with a setup like above?
- The electrical spectrum analyzer’s resolution is way too coarse to see anything. The first data point after 0 Hz (DC) seems to be 0.195 GHz, and I wasn’t able to find a way to change this. Refresh length and display memory length parameters didn’t make a difference. So there’s no way for me to zoom into the data enough to fit a Lorentzian lineshape to the beat note.
Thank you for your help!