Transmittance of bulk Silicon

Thank you for contacting Lumerical support. Before proceeding, please note that this is a public forum and anything you post will be visible to the general public. For users residing in the United States, please ensure that the files and information contained within your posts are not International Traffic in Arms Regulations (ITAR) or export controlled.

To help us solve your issue as quickly as possible, please provide the following information:

1. What device are you trying to simulate? Include diagrams if available.
I am trying to simulate silicon nanowire and silicon bulk. i am attaching *.fsp file for your reference.
2. What results are you trying to obtain? Be as specific as possible.
i am trying to find reflection spectrum ,transmittance spectrum and absorption spectrum. I am attaching the figure of transmittance of the bulk silicon for your reference. trans
3. Description of the problem or issue.
the reflection spectrum and transmiitance is not consistent with the previous reports.
I am attaching the reported graph.

4. Lumerical product and software version.
i am using trial version of lumerical-2020-R2.
5. Please attach your simulation files, including any logs.
silicon.fsp (2.3 MB) Silixon-nanowire-1.fsp (609.0 KB)

Hello @sandhyarani.s,

To measure the transmission/absorption through bulk silicon in FDTD, you should use a plane wave source placed inside the silicon, for example:


You can then use frequency domain monitors to measure the transmission through the silicon at various points. If you use a silicon slab, there will be reflections at the interfaces between the silicon and the air, so your results will not match those of bulk silicon.

You should also check the material fits in the Material Explorer, to make sure the material properties (in particular the imaginary parts of the index) are accurate:

As for the silicon nanowire, your simulation looks reasonable to me, but I would recommend you move the transmission monitor away from the wire to get better transmission results.

I hope this helps. Let me know if you have any questions.

I have measured transmittance of silicon nanowire by moving the
frequency domain monitor away from nanowire as suggested by you. i am
attaching the spectra what i got from that.
i found that the transmiitance spectrum is not very smooth and also the
spectra seems to be different according to the concept of optical
transmittance in material.


Hello @sandhyarani.s,

If you would like a smoother spectrum you can increase the number of frequency points recorded by the monitor, which can be found in the global monitor sections:


Regarding the shape of the spectrum, light scattered by or passing around the nanowire will also be transmitted through the monitor, so the transmission result will depend on the exact geometry of the source and the nanowire. I don’t think this transmission spectrum should be expected to be the same as the transmission spectrum of bulk silicon.

Let me know if you have any questions about this.