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High-frequency relative intensity noise, mode-suppression ratio and cross-spectra of low-frequency optical and electrical noise were measured in 1.55 /spl mu/m strained-layer multi-quantum-well (MQW) InGaAsP/InP laser diodes, which underwent accelerated aging. The deterioration of the linewidth and side-mode-suppression ratio is accompanied by an increase in the negative correlation between the optical noise and terminal electrical noise in the vicinity of the threshold. This is explained by recombination processes through point defects in some areas of the active layer, which contributes to an intensive Lorentzian noise. An absence of both the Lorentzian noise and negative correlation between optical and electrical fluctuations at threshold indicate higher quality laser operation. It is, therefore, concluded that measurements of the correlation factor could be used as convenient method in laser quality screening.

Low-frequency noise characteristics and their changes during short-time ageing of InGaAsP multiquantum-well distributed-feedback laser diodes were measured with the aim of investigating the reliability of devices. The noise characteristics reveal obvious differences between the stable and degrading lasers operated near the threshold region - an excessive Lorentzian type noise with negative correlation factor was observed at the threshold of degrading devices. The behaviour of the degrading lasers during ageing could be explained by migration of point recombination centres at the interface of an active layer, and by the formation of defect clusters.

The optical and electrical low-frequency noise spectra and their correlation factor of multiple quantum well strained-layer Fabry-Perot (F-P) and distributed-feedback (DFB) InGaAsP/InP laser diodes have been investigated as a function of temperature and current. Particular attention has been given to the optical and electrical fluctuations due to mode-hopping effects, which are observed in the F-P lasers at specific currents and temperatures. Both the electrical and optical noise during mode hopping have a Lorentzian type spectrum, and are very strongly correlated and very sensitive to temperature and optical feedback.