I have seen the phrase 'modal gain' used in the context of photonics. Researching this phrase, I found this resource, which explains it as follows:
Modal Gain: which is the material gain adjusted to take into account the poor overlap that always exists between the optical mode and the electron envelope function in the quantum well.
(I.e: modal gain=material gain* confinement factor)
However, I don't find this explanation very illuminating. My understanding of photonics is at a novice level, so part of the problem is that this explanation is too advanced for me to understand. So, as a novice-level explanation, what is 'modal gain'? Furthermore, I am especially interested in what 'modal gain' means in the context of laser diodes. So what is 'modal gain' in the context of laser diodes?