February 10, 2023 at 3:59 amJiang XiongSubscriber
Esteemed Ansys technicians,
We are currently studying the wave propagation behavior in a dielectric slab, when a monochromatic wave (a sinasoidal wave with a single frequency) is incident from the left (input port). It seems in Lumerical, only Gaussian pulse with a finite spectrum, no matter how narrow, is allowed? Could you please kindly let us know the correct setting, if there is? I guess there is not any theoretical conflict between a monochromatic source and the FDTD algorithm itself. Otherwise, is there any alternative solution, if the monochromatic properties are exclusively concerned in our specific case.
We are looking forward to your suggestions and many thanks!
February 13, 2023 at 8:23 pmGuilin SunAnsys Employee
In general, FDTD uses pulse as source signal, which is more efficient than a sinusoidal wave. Please refer this post:
Ansys Insight: FDTD 为什么采用脉冲光源激励而不采用正弦波光源
you can set a relatively narrow spectrum (longer pulse), and only record the single frequency in the frequency-domain monitor.
If you really want a single wavelengh injection, you can set a cw source:
but you will not be able to use frequency domain monitor, since the Fourier transform requires the signal to decay completely.
In summary, you can simply use a relatively narrow spectrum to get the monochromatic result in CW, steady state from DFT monitor.
February 14, 2023 at 9:47 amJiang XiongSubscriber
Thanks a lot for the suggestion!
We are now trying the narrow spetrum to perform the simulation.
Meanwhile, when I was checking the CW setting via the website link you provided, it seems the "CW source page" in the article entitled "1D cavity laser using 4-level 2-electron material" would direct to a wrong page:
Would you please help check and let us see the correct page?
Thanks again for your patience!
February 14, 2023 at 5:57 pmGuilin SunAnsys Employee
I am not sure why it happens but I can successfully land to that page: https://optics.ansys.com/hc/en-us/articles/360042192813-1D-cavity-laser-using-4-level-2-electron-material
Please note that narrow spectrum means longer pulse, which will increase the simulation time. To get accurate DFT result from the frequency domain monitor, longer simulation time is required.
The CW source cannot give you accurate DFT result, since the signal lasts.
February 14, 2023 at 11:46 pmJiang XiongSubscriber
Yes, the website you mentioned is indeed available, but the "CW source" page it suggests to refer is not (please see the blue link in that page in the following screen shot) .
Thanks also for your reminding on the simulation time and I quite agree with your comment. In fact, currently we are more concerned about the time-domain behavior of the signal.
February 15, 2023 at 1:13 amGuilin SunAnsys Employee
Thank you for pointing out that link. I thought it was the above "FDTD cw source" which was my file link. the "cw source" page is here https://optics.ansys.com/hc/en-us/articles/360042192813-1D-cavity-laser-using-4-level-2-electron-material.
February 15, 2023 at 12:16 pmJiang XiongSubscriber
Thanks Guilin, but I guess you accidentally copied the wrong website address of the "CW source" page. The address is identical to that in the previous reply, which still directs to the article "1D cavity laser using 4-level 2-electron material".
So would you please help offer the correct "CW source" page again? Many thanks and I'm really sorry for the inconvenience.
February 16, 2023 at 7:20 pmGuilin SunAnsys Employee
You are right. The forum post is here https://forum.ansys.com/forums/topic/ansys-insight-single-frequency-cw-source/
February 17, 2023 at 1:56 amJiang XiongSubscriber
Yes, we see the post now. It would help us a lot.
Thanks so much for your patience and quick responses all the time!
February 17, 2023 at 8:11 amxudong ZhangSubscriber
I'm also interested in this setup and I have learned lots about how to create a custom source time signal.But it seems that my "users input Setting"is unavailable.Could you please provide more detailed steps on how to import custom signals?
February 17, 2023 at 4:53 pmGuilin SunAnsys Employee
Please refer the script file in the example. You need to use script to load the signal.
In many many cases it is absolutely no need to use monochromatic light source. Please think it again, and read above replies.
The only cases are the listed examples for few nonlinear simulation, or you only need to know time domain result, without separating the amplitude and phase, as the simulation is at steady state which records instanteneous fields from a time monitor. You cannot use frequency domain monitors, as it violates the Fourier tranform theorem.
February 18, 2023 at 3:08 amxudong ZhangSubscriber
OK, I'll try again. Thank you for your timely reply！
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