i've been studying interferometers for some time now and though i understand why fabry-perot interferometers and ring resonators give a resonance pattern, somehow, i couldn't quite grasp the reasoning behind "resonance" patterns in mach-zehnder interferometers. in other words, what my question really is IS, unlike FP and ring resonators, light doesn't get coupled back into an MZI, so how does it even produce resonance?
in the end i realized i have been trying to understand the "resonance" graph all wrong. first of all, it would be wrong to describe the graph above as "resonances" as you can see dips instead of resonances but the previous TA always uses the term "resonance" which probably added to my confusion. the graph above, in fact, does not show resonance peaks but rather interference.
so, basically, the dips in the wavelength vs attenuation graph above shows the wavelengths at which destructive interference occurs due to the difference in arm length of the interferometer. changing the arm length difference results in (wavelength shift or FSR change?). furthermore, as can be easily noticed, the graph (regardless of the dips) does not follow a straight line. in fact, it is relatively bent with a minimum value of about 12dBm at 1540nm. this bending is due to the attenuation of the waveguide itself which shows it has been optimized for 1540nm use.
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