Cascade semiconductor lasers for telecommunications

The topics discussed include: improving the noise figure with cascade lasers; bipolar cascade lasers; and noise and correlations in cascade lasers. The noise figures for various directly modulated links tend to decrease with increased link gain. Since the received noise is limited by the shot noise floor, large enhancements in the NF must be made through improvements in the intrinsic link gain and hence the modulation efficiency. Bipolar cascade lasers are a new class of laser structures which can be directly modulated and do not have any of the conventional restrictions on loss of electrical signal strength or increased noise. The correlation in the photon emission in lasers connected electrically can be experimentally obtained by measuring the correlation in the photon intensity noise spectral density of the lasers. Noise correlations limit the improvement in noise figure despite the enhanced link gain.