Learning Forum

[Dharmander Malik]

Hi,
I am working on your example, "GaAs-AlGaAs Electro Absorption Modulator". I wish to know two things :
1. How is the lumerical charge software obtaining absorption spectra for AlGaAs/GaAs structures internally?
2. I tried to do the same simulation for other materials like InGaAsP/InP but could not get the QCSE behaviour, and the absorption spectra were also distorted. It would be a great help if you could suggest something regarding it how to do the simulation for other materials correctly. 

Please find some time to answer the queries. Thanks

[Guilin Sun]

A1: CHARGE only solves charge transportation. It does not simulate the optical frequency response of absorption. In the example, it mentions in Step 2: "After running a single CHARGE/MQW coupled simulation, absorption is automatically calculated at different bias points. The absorption coefficients and perturbation to the real part of the refractive index for TE and TM modes are plotted. The transmission for the TE mode is then calculated and compared with the literature. " So it is the MQW that calculates the absorption.

 

A2: I an not sure what does "the absorption spectra were also distorted" how to define the distortion and what is the reference here? 

As long as the optical and electrical properties of the materials, and structures are correct, with proper meshing the simulation result should be correct. You may need some time for the example.

 

 

[Dharmander Malik]

Thanks for your reply. I will try to give you more detail this time so that you can understand the situation better.

1. I have gone through the mentioned Lumerical example thoroughly. It is not clear how does the software obtain absorption spectra for AlGaAs/GaAs structures internally? Which model/equation is Lumerical using to produce the absorption spectra internally? It is quite important to understand if someone wants to use other material for QCSE design that may not be persent in the material library. 
2. The distorted absorption spectra mean that the obtained spectra shape is not theoretically expected, like the one shown below which I obtained from InGaAs/InP QCSE simulation (the curve is somehow inverted). It may be because the default material properties for the other materials is not so well defined. 

1. I am also looking for another possibility, such as importing the absorption spectra of a structure calculated in other software at zero bias. Then, it can be imported into Lumerical and then checked for its bias sweep dependency (QCSE behaviour in Charge). Any suggestion on how to do this?

If CHARGE only varying the absorption spectra with bias then where is the absorption spectra information at zero bias. Any lead would be a great help.

Thanks 

[Guilin Sun]

It is the cosimulated result by CHARGE/MQW for the obsorption. Currently MQW is 1D so it might have simplified somethng.

In some cases the material properties have to be well matached but it might be difficult to obtain them accurately. This might cause some issues. Here is the introduction for MQW physics: https://optics.ansys.com/hc/en-us/articles/4408088112915-MQW-Solver-Physics

 

[Dharmander Malik]

Hi, I'm still facing the same problem. My question is still, " How software calculates absorption spectra". Since modal properties such as effective index are calculated in Mode Solution, I suspect this absorption spectrum (at zero bias) should be coming from simulation in Mode Solution. But again, how then this absorption spectrum is imported into the Charge Software? In which file is this information stored then? Please provide information on this.

[Guilin Sun]

Not sure if you read the MQW solver physics.

no, not  from MODE Solution.

You cannot directly import it into CHARGE. It is co-simulated result with CHARGE and MQW. MQW calculates the absorption. but it needs energy levels calculated from CHARGE. This is why they have to be coupled in simulation. The whole simulaiton procedure is given in the example.