Great to see you were able to import the correct gain profile. Sorry for a bit late reply.
I see you fixed some issues in your previous version (2) of the gain file, such as having some quotation marks in the first and third row and having carrier density in the units 1/cm^3 instead of 1/m^3. Just for future reference, here is the description of the structure of the gain file:
The fitted gain artifact near the simulation band edges is expected, since the fitting algorithm uses periodic boundary conditions, so it tries to make gain at the first and last frequency equal. This is usually not a problem in the laser simulation. But some tweaking can be done, such as reduce the rolloff input argument in the mczfit function, which specifies the percentage of simulation bandwidth over which this rolloff will happen. Another thing is to increase the simulation bandwidth (sample rate input argument to mczfit function and a similarly named option in INTERCONNECT root element). This will make gain curves more symmetric and there will be less artifical rolloff (but the simulation will take longer).
However, in this case you should probably also try to simulate for higher input powers, in which case this spurious mode may vanish (currently the power is around threshold).
I noticed that the average carrier density (measured by OSC_1) is more than 2e25 near threshold, which is the highest carrier density in the input gain profile, so simulation probably won’t work very well. It is best to check all other parameters and make sure they are reasonable (such as recombination rates). Once you get reasonable LI curve, hopefully the spurious mode will not be a problem anymore.
You can use both modal and material gain. The difference between them is just that the modal gain is material gain multiplied by the mode confinement factor. So if you use modal gain, you should set the mode confinement factor to 1 (since it is already included), while if you use material gain you should define the actual mode confinement factor.
Imported gain must be defined as a function of carrier density, so you have to be able to convert your experimental current into carrier density, if your measured gain is a function of current.
This is a selection of some other important laser parameters:
Nonradiative coefficient C (cubic) is Auger recommbination, nonradiative coefficient A (linear) is SRH (trap assisted) recombination, and radiative coefficient B is usually spontaneous recombination rate. Note that you need to have nonzero radiative recombination, otherwise there will be no lasing (there is no “spark” to cause lasing).