problem of grating coupler simulation in 1310nm


dear all
I have built a structure of my own grating coupler.When I run the programm in 1550nm wavelength range,the result seems to be right.However,when I run the programm in the 1310nm wavelength range,the result seems to be wrong,which means that the transmission of the T monitor is too small.The similar question also happens in the 2D FDTD of grating coupler on your official website.I have do some sweep and optimization while it still didn’t work.What confused me is that whether the grating coupler can only just work right in the 1550nm wavelength or somewhere is set wrong in my simulation.The below is my simulation.Please help me check it. Hope to get your feedback.Thanks a lot.Si_grating_coupler_2D_input_1310nm.fsp (554.2 KB)


Hi @jbwei
There are several parameters that decide the performance of a grating coupler: period, fill factor, incident angle, incident position, etch depth, thickness of the SiO2 substrate, thickness of the SiO2 cladding, number of grating periods. Among them, etch depth and SiO2 thickness are decided by the fabrication process.
The primary impact of these parameters is that they change the central wavelength. This can be found from the Bragg condition to find the central wavelength :

One should keep in mind that when the grating coupler central wavelength change, so too does the effective index, which is wavelength dependent (dispersion), neff(λ)

Best regards


Hi @jbwei

Your simulation file seems to be set properly. My only concern is about the geometry and weather or not is supports TM modes at 1310 nm. I used a TE mode to be injected from the fiber and it shows ~12% transmission at ~1260 nm.

Do you have a geometry from a paper that supports TM modes at 1310nm? If you want to design your own bragg grating, please note that you need to start from a geometry as expected by theoretical calculations. Optimization and sweep function will work best for final tunings, otherwise they might fail if your initial value are set way off from optimized results.


dear konslekk and bkhanaliloo
Thanks very much for your help.Both of you mentioned that a strong corelation between optimization results and the original setting condition of model,which means that the original setting of the model combined with the optimization condition result in the final optimization results.If the original parameter setting is wrong,the optimization will do little work.So If I want to get a ideal optimization result,I must set the original parameter prober. Is my understand correct?
furthermore,if I can’t get the result I want ,can I add the maximum generations and the generation size in the optimization setting,just as show below.


Hi @jbwei

Yes, you are right. By increasing maximum generations and the generation size you can hope that you get more precise values. This is being said that in most cases you get a good value after few generations. Thus, I would say that increasing generation size in some case might be more useful than the number of maximum generations. You can read more about the particle swarm optimization here to see how the algorithm works.



dear bkhanaliloo
I have done an optimization of the parameter FF and GC_pitch and want to get the optimum value of transmission in the 1550nm wavelength.The picture below is the result I optimized.

however,when I set the parameter FF and GC_pitch to value as the same as the optimized result,which is shown below,

the result of the transmission in the 1550nm wavelength is not right.,which means the transmission in the 1550nm is too small.

I dont know why the result of the simulation is not the same as the optimized result although I have set the parameter FF,GC_pitch to the same value.Can you help me find the reason? Hope to get your feedback.Thanks a lot.

Si_grating_coupler_2D_input_1550nm.fsp (3.1 MB)