Coupling modulated ring resonator

I want to simulate a coupling modulated ring like the one presented here:

I want to run a time domain simulation to depict the High pass filter effect of this modulation technique. fig. 2B

I tried this on Interconnect. But I cannot get the desired output.
Coupling Modulated ring1.icp (3.0 MB)

I don’t know exactly what the problem is. The S-parameters show the expected change in the output spectrum as the DC input changes betweem 0 and 1.
Coupling Modulated ring_Spar.icp (380.0 KB)

Hi @aya_zaki,

I haven’t looked into details in this application yet, but at a first glance, the ‘Variable Coupler’ in the circuit should have opposite phase shifts in the upper and lower branches. according to the reference. Also, could you please help me to understand the modulator design? I will keep looking into it, meanwhile, please keep me updated if you make any progress on your end. :slight_smile:

Hi @gwang,

Thanks for your reply. I will elaborate a little bit on what I am trying to do here using Interconnect.

In order to overcome the problem of limited modulation bandwidth that accompanies any high Q ring resonator, a new modulation method was proposed in which the coupler is modulated instead.

The earlier version of this design wasn’t differential. It used a single variable coupler. This is the case I want to investigate. According to the paper, there is a high pass filter effect in the coupling modulated ring when a long stream of ones occurs as shown below.

I would like to depict this in the simulation. So, I built the circuit below. I used the scripted optical modulator to model the variable phase shift in one of the arms of the variable coupler.

However, this is what I get. No high pass filter for long ones.

To double check the static frequency domain simulations are okay, I used an ONA to find the spectra of the ONE and ZERO states. There is something quite confusing here too; the ONE give low optical power while the ZERO gives high power. This contradicts with what happens in the time domain.

Hi @aya_zaki,

Yes, the modulated signal is the opposite of the driving signal, that’s generally due to the modulation point; modulated on the middle point of the failing edge.

I adjust the circuit a bit according to the following figure in the paper:

However, I still don’t see the droop effect mentioned in the paper. I will keep digging in this problem and follow up with you. Please let me know if you make any progress as well :slight_smile:

Thanks for your help, @gwang. But what do you mean by modulated on the middle point of the failing edge?
Is it that you changed the arm where the OM is inserted?

Hi @aya_zaki,

By modulation point, I mean at what frequency point on the modulator transmission curve the driving is modulated to. I found the following figure online

If you modulate your driving signal on the point “Quad0” and the driving signal (which in the figure is indicated by the square wave at the bottom) is centered at the “Quad” with the amplitude equals the distance from “Peak” to “Null”, then the modulated signal is in opposite of the driving signal.

I hope this is clear :slight_smile: