Low quantum noise laser diodes

It is demonstrated that laser diodes can be optimised for low quantum noise operation. Attention is given to the excess quantum noise arising due to non-orthogonal longitudinal modes in laser diodes with asymmetric facet reflectivities. It is shown that in symmetric high-reflectance faceted laser diodes such excess noise is eliminated, and thus this is a good design option for low quantum noise devices. It is further shown how the threshold current/quantum efficiency ratio of this structure may be optimised. This shows the importance of knowing the internal loss and facet reflectances, and then using an appropriate device length. The superior spectral purity of these devices is also indicated. Such devices are recommended for investigating sub-Poissonian light, using quiet pump sources. Squeezed light generation may be possible using asymmetric high-reflectance devices (∼ 70-100%), with less asymmetry than is normally used (∼ 10-90%).