Learning Forum

[Altair45]

Good Day,
I calculate the transmission in coupled resonator optical waveguide with phase-shifted bragg grating. A few days ago, I posted my transmission result with some errors that -2.5dB loss is confirmed in the pass bandwidth and wavelength shift. As following the advice, I tried to optimize the result by changing the simulation time, PML layer, and mesh size. But, there are no noteworthy changes in the data like the attached graph.

I check the DFT monitor, located in every phase-shifted region so that the transmission is decreased when the light propagates every grating.

What is the reason for the gradual loss? When the phase shifter is present, no loss in the data.
Kind regards,

Taylor Kim

[Guilin Sun]

This might be a more theoretical question. As you mentioned, with the phase shifter, the transmission is good. This might be the reason people use it.

When light is not well confined inside the waveguide, scattering causes losses. Thus the longer the device the smaller the transmission. You can verify this by using top and bottom as well as side monitors.

You may also try EME in MODE, as it is more efficient for long repeated structures. Please refer to this example:

https://optics.ansys.com/hc/en-us/articles/360042304334-Bragg-Grating-full-device-simulation-with-EME

 

[Altair45]

Thanks for your advice. So I'm trying to investigate the effective index by calculating it both theoretically and simulationally.

 

But, I wondering if the MODE simulation is suitable for the coupled resonator optical waveguide (CROW) based on phase-shifted bragg grating.

 

As I know, the MODE is analyze the object only in 2D, but the CROW structure is varying for the z-axis due to the phase shifter as I attached images below. 

 

In this situation, how can I simulate the effective index and mode profile in the MODE simulation

[Guilin Sun]

You will need to have a math definition for "the effective index" for such devices.

FDE in MODE solves modes in a waveguide cross section.

When it is ring resonators cascated, it is cavity so you will need to use 3D FDTD to simulate such cavity and then extract the result and derive the effective index if possible.

We do not have any similar examples.