Hi Narendra,
It is not necessarily that simple a question as a lot would depend on your preliminary design which you need to have an idea of before getting into the products. Let me touch on a few items for both products to see if I cannot clarify a few things for you because OptiBPM may be able to support your structure but you cannot simply make the sample a high contrast as it complicates things.
OptiBPM
- By simply changing the materials so you have 1.5 to 1 those 4 um waveguides which were single mode in the sample (1.44 to 1.46 contrast) are now most definitely multimode so when you hit the split your fundamental mode and couple to other modes as well which leads to some of the issues as you are now going to see the beating between a number of modes.
- The full vector OptiBPM (Simulator option in 3D Isotropic simulation parameters) is more tolerant of high refractive index contrast.
- The resolution in the sample is not adequate for a high contrast simulation.
- If you drop the waveguide widths to 1um (single mode), increase your mesh to 10 points/um, propagation step to 1, and run a Vector simulation you will see that OptiBPM is able to obtain what appear to be reasonable results.
OptiFDTD
- Provided you use adequate resolution (minimum of lambda/(10n) OptiFDTD can readily model high index structures.
- One of the problems with OptiFDTD is that due to the resolution requirements simulations can be resource intensive, especially in 3D. You need to keep an eye on the size of the domain as the resources required for a 3D simulation that is orders of magnitude larger than the source wavelength may be more than you have.
- One thing to look at is that the sample you are working with is 800 um long because it is low index contrast and therefore low confinement and requires that distance to do the split. Moving to high index results in higher confinement which means your split can be accomplished over a shorter distance. Typically SOI photonics based structures are not on the scale of millimeters because they do not need to be.
Regardless of what application you ultimately end up needing I strongly encourage you to have a very good understanding and expectation of the parameters of your structure. This expectation will guide you in the decision to the nature of the numerical algorithm you need for your research.
Scott