Learning Forum

[Z.Shahrabifarahani]

Dear all,

In my simulation file, I am aiming to calculate the transmisson of a beam with wavelength 1064 nm guided through an optical nanofiber with diameter 700 nm which also has a slot cut through it's waist, shown in the Fig_01. 

 

My simulation setting is as follows:

- FDTD region: 4 um * 4um
- PML: 28
- Auto shutoff min: 1e-10
- ONF diameter: 700 nm
- Source: beam with 1064 nm in wavelength  and 10 um before the slot cut
- Slot cut: A rectangle with triangle-ends with total length 17 um and width 350 nm.
- Monitor position: 25 um away from the slot cut (Extra mesh grid with mesh size 3 nm * 3 nm was added at the monitor position for higher accuracy in the transmission calculation

However the mode profile at the monitor position has such a distributation:

As you can see, The mode profile does not reach zero at the end of the FDTD region.
Based on my previous experience, I am sure that increasin the simulation region will not fix this problem.
I wonder why it happens and how I should solve this problem.

Thank you in advance,
Zohreh

[Guilin Sun]

It is better to check the mode using a mode source on the waveguide.

For the monitor, it records all the fields excited by the abruption of the waveguide. eg, some higher order modes are excited this is why the field intensity does not go zero.  You can use ports or expansion monitor to check the higher-order modes: Using and understanding Mode Expansion Monitors – Ansys Optics

[Z.Shahrabifarahani]

Thank you for your reply.
That's true, it looks correct with mode expansion monitor.