Noise enhancement in laser amplifiers caused by gain nonuniformity

We have calculated the noise-enhancement factor of a semiconductor laser amplifier with a very thin active region. This (somewhat academic) model exhibits large Petermann´s K-factors. However, the calculated noise-enhancement factor K¿ is only about half the K-value. The reason for the discrepancy is that in evaluating K¿ the radiation modes of the guiding structure have been taken into account. Similar conclusions have been reached for realistic laser models. These theoretical considerations show that gain-guided laser amplifiers are not as noisy as was originally thought.