Hi every body,
I want to design a ring coupled to a bus waveguide and obtain critical coupling.
I am doing simulation in 2D, so I use effective index method to replace the 3D structure by 2D one. The waveguides are of silicon with the width of 500 nm and the height of 220 nm, the radius of the ring is 10 um. And the fundamental TE mode is used. In fact, I got the transmission spectrum and I see the dips, but they are very shallow and it seems that I could not reach the critical coupling yet ( in order of 10^-5 dB!). I changed the gap between the ring and the bus repeatedly, although the spectrum changed, but still the dips were really shallow! Could you please guide me to solve this problem?
I have some more questions:
1- When we say the critical coupling means equivalence of internal loss with coupling loss, and it causes a case where we have destructive interference in the bus, and so no power at output, what really happens?
2- For an ideal case, where α=1 (it means that internal loss of ring is zero), and so for getting critical coupling t=α=1 and κ=0, how the critical coupling happens? It seems there is no coupling to the ring because of zero coupling coefficient.
Thanks in advance,
Zeinab
Thank you Dear Smrity and Dear Somayyeh,
I usually check material properties before all simulations, It could not be the source of the probelm, because even when I used fixed refractive indices, the results did not changed.
It seems that changing mesh size also does not affect the results.
And finally, changing the gap does not change the resonance wavelength. In fact, I do this to get critical coupling for the predefined resonance wavelength, to see deep notch at this wavelength. But, it does not change the results much.
There is relationship for the transmission of ring coupled to waveguide:
T=(alpha-abs(t))^2/(1-alpha*abs(t))^2...
Recently, I am making a conclusion but I am not sure :) Just share it here, if some one has any comments, I would be happy.
When, I am doing 2D simulations, it seems loss is very close to zero, so the alpha in the above formula is very close to one, it means that the above equation could be rewritten as follows when we consider alpha=1:
T=(1-abs(t))^2/(a-abs(t))^2=1...
So, it is probably why, I do not get deep dips. Even for resonance wavelengths, the transmission (at dips) is near one.
So, let me ask a more general question, is it possible to obtain critical coupling for lossless case (where alpha is 1)?
Sincerely,
Zeinab
Hi , I am doing a hexagonal ring resonator structure b/w 2 waveguides using photonic crystal. What is the formula that can be used to get the design parameters of a ring resonator? Design parameters in the sense ., Radius and thickness of the diaphragm, lattice constant, radius of hole, radius of hexagonal ring & gap b/w ring and waveguide.
Thanks and Regards in advance
Yashaswini
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science