Learning Forum

[StanleyLim]

Dear all, 

I am having a problem in reproducing the propagation loss a waveguide using VarFDTD. The result [1] I am interested in reproducing is as follows: 

where the thickness of lithium Niobate (LN) is 300nm, the PMMA waveguide thickness is 500nm, and the silicon thickness is 2 microns. I used VarFDTD to set up this waveguide, and sweep the waveguide width. I would like to reproduce figure (c) result at the wavelength of 1550 nm. Here is my VarFDTD setup:

where i set the waveguide total simulation length to be 200 microns, and two monitors are set in the beginning and at the end of the waveguide to measure the transmission spectra at the beginning (T_begin) and at the end (T_end) of the waveguide. Then, I substracted the T_begin by T_end to extract the propagation loss of the waveguide. This is what I obtained after few attempts: 

 

It seems like the result is upside down compared to Fig.(c), and the magnitude of the propagation loss is off. Could you please point out my mistakes or provide some comments regarding to this issue? Thank you so much in advance. 

 

[1] Yu, Zejie, et al. "Photonic integrated circuits with bound states in the continuum." Optica 6.10 (2019): 1342-1348.

[Devika]

Hello, 

We dont have access to journal papers. Ansys Insight: Ansys Innovation Space —- Forum and Feed

Can you elaborate which tool the author used to calculate propagation loss? MODE or FDTD?

Also which monitor are you using in your simulation?

Thanks and regards

Devika

[StanleyLim]

Dear Devika,

Thanks for your reply. In the paper, the authors mentioned that one used FDTD to simulate the propagation loss for the waveguide. I used frequency-domain field and power monitor.

Best regards

stanley

[Devika]

Hello, 

Thanks for additional information. 

DFT monitors will record the power propagating through them. This will not necessarily reflect the actual loss, mainly bcz part of the power will not be in the waveguide's mode. 

I would suggest to use a mode expansion monitor so you can get the actual coupling to the mode supported by the waveguide.

Futhermore, I would also suggest to use FDTD to match the results.

Thanks and regards

Devika

[Devika]

 

Hello Stanly,

Correction in my previous response, for straight waveguide propagation loss can be calculated simply using FDE. Waveguide (FDE) – Ansys Optics

Also, the post written by Guilin will be helpful.

Ansys Insight: Why my simulation result is different from published paper or experiment?

Thanks again

Devika

 

[StanleyLim]

Dear Devika,

My very first attempt is using FDE, but I realized that FDE only takes into accounts of the material's imaginary refractive index (I ran two different simulations, one with actual material parameters with , one with object-defined material parameters without imagnary refractive index). It turns out that the one without imagnary refractive index gave no propagation loss. This is why I used VarFDTD (as the authors mentioned). I will check out more carefully the link you sent me. 

Thank you