Help in laser simulation in COMSOL

[Pooya]

hi
im supposed to simulate a vcsel laser for my thesis
i got problem in selecting physics.. i should check its heat transfer and threshold current but i don't know which physics should i choose ! does anyone know about vcsel's physical structure in Comsol ?

by the way does anyone know that how can i simulate the layers of its resonator and its contacts in COMSOL?
should i use its Pde equations ?
thanks a lot

 

[Pooya]

Tnx
well i think i have to change my question ..
does anybody know with which simulators i can simulate a vcsel laser ?
i have installed Rsoft , Comsol , FDTD and Silvaco on my computer
i have to give some conclusions like thermal , threshold current and the gain of this laser
is there anybody here who had simulated this kind of lasers?
tnx a lot

 

[Mech_Engineer]

When you say you want to simulate a VCSEL laser, do you know what specific physical processes of the laser are you need to simulate and analyze? You need to take a logical approach to identifying the physical processes at work in a VSCEL first; all of the expensive software in the world can't help you if you don't first know what you're trying to model. It might be for example that the conversion and/or generation of photons within the laser cannot be modeled in software, but instead is calculated using quantum physics equations and MatLab. Most importantly, you will need to confirm any simulation results with some sort of "back of the envelope" analytical calculations to make sure the simulation isn't giving you junk data due to some unanticipated issue.

You should also identify an analytical process to use for design/analysis of the laser module, maybe from an academic book or reference. How are current companies designing and analyzing VCSEL lasers? What optimization criteria do they need to balance? I recommend you also read up on current state of the art regarding design and simulation of VCSEL lasers, because the analysis you're looking to do has already been done by somebody.

SPIE has a digital library that is a very valuable source for this sort of research. Take for example this paper I found: An efficient electro-thermo-optical model for vectorial and 3D VCSEL simulation (Debernardi 2009).

 

[Pooya]

tnx for your attention
yes , I've been studying about vcsel laser for a year and i know its' structure
the problem is i don't know how can i simulate the structure!
in vcsels we got substrate , bottom dbr , active region , top dbr (im supposed to use hcg structure instead) , and contacts...
ive read about 20 atricles about it but i haven't had any example of it's simulation...
for example i don't know for measuring the heat transfer of it i should use equations or the graphic simulation of it !
the problem is i don't have any example of it...

 

[Mech_Engineer]

To understand how to model it, the structure is important but more important from a simulation standpoint are the interactions. This is analogous to a flow chart- given inputs what are the outputs and what are the intermediate steps.

So, what parameters are you specifically interested in regarding the VCSEL? It seems like a paper like this one should start you down the right track: http://www.sciencedirect.com/science/article/pii/S0924424700005215

 

[Pooya]

Tnx.
All i want to do is make a simulation of a vcsel structure.. i should change some parameters like QWs in its active region and then i should check the temprature of its active region and its threshold current!
I should apply voltage to the top and the bottom contancts which i should put in my simulation
As u know my inputs are voltages and my outputs are threshold current and thermal

My problem is i don't know how to simulate the structure!
In some softwares like comsol and FDTD and Rsoft we can make a graphical structure of the device
Is some others we should design our structure by coding

I don't know which one i should use
I need some help in it ...

 

[Mech_Engineer]

It seems to me you don't yet grasp the high-level idea of how a problem like yours would be simulated... No off-the-shelf simulation software will just simulate a VCSEL without some inputs on your part defining what should be simulated and how. What you're looking for will be a multi-physics model incorporating 2-D or 3-D electrical simulation coupled with a thermal analysis, software like Comsol or ANSYS Multiphysics is capable of this but is a generic tool; you need to set up exactly the simulation physics regimes, geometry, material properties, and boundary conditions you're after.

Please review one or all of the papers I've provided links to and do some research of your own regarding simulation of VCSELs. The link I provided earlier seems to cover the exact simulation you're trying to create, your best bet is to read it (or another publication like it).

 

[Pooya]

Let me give you an example of a conventional vcsel structure ...
Suppose I am going to simulate these parameters in COMSOL :
p-DBR : (20 periods) - 7.5um x 2.6 um -- material = Al0.625Ga0.375As
Spacer (between p-dbr and Quantum well) : 7.5um x 0.23um -- material = Al0.6Ga0.4As
MQW : 0.061um
Spacer (between n-dbr and Quantum well) : 7.5um x 0.23um -- material = Al0.6Ga0.4As
n-DBR : (29 periods) - 7.5um x 3.7729 um -- material = Al0.625Ga0.375As

First i make a 3D structure and i choose heat transfer and electric current in physics
next i have to choose the geometry.. i don't know which one i should choose! The cylinder? The block ?
after that i should do the layering ..
and...

Can you give me a hint ?

 

[Mech_Engineer]

My personal feeling is your getting too bogged down in the details... FEA software is only a tool and can only be a effective as the operator using it.

I suggest you think of your model from a practical standpoint; where are the current sources coming into and going out of the VCSEL? That's where you define the boundary conditions for your electromagnetic model. Separately, you'll need to decide where your thermal model's boundary conditions are and set those as well.