Hello,
The optical gain difference in the MZM arms allows to balance the modulation depth which is important for controlling the amplitudes of the generated comb lines. If you will change the gain difference, you can clearly see the impact on the comb spectrum measured at the “Dal Port Optical Spectrum Analyzer”. So, the difference of electrical gain on the MZM arms allows fine-tuning of the optical signals entering each arm of the MZM to achieve the desired phase and intensity modulation, which directly impacts the comb spectrum.
Hope this helps?
Warm Regards,
Saurabh Bedi.