The Linewidth Enhancement Factor of Intersubband Lasers

The linewidth enhancement (alpha-factor) of intersubband lasers was initially expected to be zero. However, nonzero values have been found in experimental investigations. This paper will give further details on how this controversy has been recently resolved by showing that counter rotating terms, usually ignored in simulations are the actual fundamental origin of nonzero a at peak gain even without inclusion of nonparabolicity and many-body effects, which are however needed to explain negative values. For laser without inversion conditions, a is found to be larger, but still at the same order of magnitude of conventional inverted medium lasers.