Unable to reproduce literature results (Reflection and Transmission in a single mode laser)

Dear Lumerical support team/users,

I am trying and evaluating the suitability of lumerical for my simulation purposes. In a first step, I am trying to reproduce literature results (paper attached). For instance, I am trying to reproduce the transmission and reflection from a slotted waveguide from Lu et al, IEEE photonics technology letters, 22, 11 (2010). I am attaching the paper and have highlighted the relevant simulation parameters. To summarize,

Structure : Ridge waveguide with etched slots

thickness of ridge: 2 micron, depth of ridge: 1.85 micron, slot width:1.1 micron, slot spacing: 7.87 micron, slot depth:1.35 micron

Aim: To calculate the reflection and transmission from the device at 1.55 micron for the fundamental TE mode and reproduce the quoted value of 0.43 and 0.4 respectively.

Method: I am using both EME and varfdtd to reproduce the results.

Problem:

  1. I am not able to get the desired results. the s-parameters obtained from the EME do not agree the transmission and reflection value quoted in the paper.

  2. The transmission/reflection value from fdtd power monitor also do not agree with the paper.

I am new to this tool. Apologies if I have done something wrong. I am attaching both of the files (eme and fdtd).

Please help me in this regard.
singlemodeieee.pdf (420.9 KB) singlemodeieeepaper2fdtd.lms (421.6 KB) singlemodeieeepaper1eme.lms (640.6 KB)

Hello,

Welcome to the community. Thank you for attaching this paper, and providing detailed background. I am not exactly sure why you cannot reproduce these results without some more testing, but l will provide some suggestions and ask that you get back to me.

Both methods should be suitable to accomplish your goals; however, EME will likely be the most efficient method for the results you are interested in and very appropriate for the device you have modeled. The EME solver would also be very similar to the Scattering Matrix Method that this group used. To better sweep the parameters of interest I would recommend only having one or two slotted sections. Since the mode coupling is the same at each ridge you can increase the periodicity of these cells, or change their span, with minimal computational cost through EME propogate. Although you will have to recalculate coupling each time the slot depth is changed.

In this paper they say they are looking at a single mode, but do not say whether it is TE or TM? Both exist in this ridge waveguide. Are there clues regarding the gain material that would suggest one over the other? The TE mode will be highly confined, and so they will not be particularly effected by the DBR structure, so may be why you are seeing higher transmission. Some initial measurements of the TM reflection and transmission coefficient suggest these may be closer to the values quoted in the paper.

One thing to note is that they have given the effective indices and done the simulation in 2D. Using the 3D simulation with the 2D effective indices will likely give different results. Please change EME solver type to XZ:X propogate.

image

For more information on the EME solver please refer to these . AppGallery pages and check out the EME course for a thorough overview.

Regards,

Hi,

Thanks very much for you suggestions. It was really of great help. As suggested by you, it seems they have calculated values for the fundamental TM mode since the values I am obtaining for the TE mode is not even close. Since I don’t have any information regarding the gain media and which mode is dominant, I presume TM is used in their calculations here. However, I have still two questions which I could not able to figure out.

  1. Why can’t I reproduce the result in a 3D EME solver simulation, in other words what should I do to reproduce the results for a 3D solver? Even if I don’t use effective index, the refractive index of the layers is around the effective index values. Even if I don’t get exact results as in a XZ solver, at least I should get values around the quoted values. I don’t think I am doing something fundamentally wrong while performing a 3D calculation.

  2. Secondly, even if I excite a TM mode from a mode source in the varfdtd, I am not getting the required values, not even close. Should I not get at least values closer to the values I get for a EME calculation ( 2D XZ, X propagation). Vardfdtd uses effective index method, so should not it give the same result?

Thanks very much once again and sorry for the delay in replying.