Optical and electrical noise and quality of degraded strained-layer DFB laser

High-frequency relative intensity noise, mode-suppression ratio and cross-spectra of low-frequency optical and electrical noise were measured in 1.55 μm 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.