# How to get filtering effect for AWGs

#1

I’m following the example of AWGs https://kb.lumerical.com/en/pic_passive_waveguide_couplers_awgs_and_star.html. And set monitors in output star coupler. But all peaks are in the same wavelength. I don’t know what the error is. Could you please help me to check it?output_star.lms (641.8 KB)

Thank you very much!

Qi

#2

Hi Qi,

Could you please attach your plot here and explain a bit how you get it? I tried to run the simulation and plot the E magnitude from the monitor ‘profile’ and for different slices of the ‘wavelength’, the peaks did have an obvious difference. The following plots are for lambda = 1.9 micron and lambda = 1.2 micron, respectively.

Do you get different result than I did? Let me know how to reproduce your results

#3

Hi, guanghui

Thank you very much for your help! Here is my plot of E magnitude from "frenquency domain field and power"monitors I set.All peak are in same wavelength.

Qi

#4

Hi Qi,

I think what you want to measure is the transmission but not the E field real part. Following is the plot of the transmissions from all the monitors versus wavelength. Please note that for this simulation, the mesh accuracy is only 1, you can get more accurate results by using finer mesh.

#5

Hi, guanghui

I set the mesh accuracy to 3, and get this transmission.

The result is not so ideal for optical filter. So is the output star coupler optimized or just an example?

Qi

#6

Hi Qi,

You are right that it is only an illustration example. Actually, if you have noticed, the Star Coupler structure has a very large geometry, for this kind of structure, you have to use very high mesh accuracy. According to the structure geometry to wavelength ratio, I think a mesh accuracy of 8 probably can give better result.

I hope this could help

#7

Thank you very much for your help!

Qi

#8

Hi, guanghui

I updated the version of mode solution, and here is the transmission.. It looks better now ,but the diagram of E filed real part has no change.I can not understand why all peaks of different output are in the same wavelength. Can you explain it ?

Thank you very much!

Qi

#9

Do you mean the peaks are NOT at the same wavelength for different outputs?
I think this is because of the different lengths of the Array waveguides.

#10

Hi, aya

No, please see the diagram below.
All peaks of E field are at the same wavelength for different outputs. Interference peaks with different wavelength should be in different output. So I can not understand the reason simulation result is not expected.

Thank you very much for your reply！
Qi

#11

Hi Qi,

This effect is because of the interference of the light sources are constructed at this particular wavelength (around 1.45 microns in your case, I got around 1.32 microns in my test simulation). If you plot the source power in regarding to the wavelength, you will get something very similar to the following plot (with the dominant peak at ~1.45 microns):

f = getresult("monitor", "f");
sp = sourcepower(f);
plot(c/f, sp);


which indicates that, the source power at this particular wavelength is way higher than at all other wavelengths, so the output E-filed magnitude at this particular wavelength is also way higher for all the branches.

On the other hand, the transmission is normalized to the source power, so you get the reasonable result for the transmission.

I hope this explains it