EXFO PSO-100 Series Optical Sampling Oscilloscopes - Manual (Page 75)

Setting up and Using the Optical Sampling Oscilloscope
Optical Sampling Oscilloscope 67
Displaying the FFT Spectrum of a Sampled Signal
3. Start the sampling session.
Here is an example of a spectrum of an NRZ 40Gb/s signal. You can see the
characteristic dips in the spectrum at 40 GHz, 80 GHz, and so forth.