Excess photon noise in semiconductor cascade lasers

Semiconductor cascade lasers have larger photon noise than conventional single stage semiconductor lasers as a result of positive correlations in photon emission in different gain stages which are connected electrically in series. The photon noise of cascade lasers can be related to the photon noise of single stage lasers with scaled external circuit impedances. This scaling relation for the photon noise holds for bipolar as well as unipolar cascade lasers.