Low frequency noise spectroscopy and threshold characteristics of laser diodes

Electrical and optical noise characteristics of multiple-quantum-well distributed feedback InGaAsP laser diodes (LD) are investigated validating low-frequency noise spectroscopy as a tool for the laser diode reliability and quality evaluation. A special attention was paid to the interpretation of cross-correlation coefficient between electrical and optical fluctuations. Negative cross-correlation coefficient at the threshold could be potentially used to identify unreliable lasers. We demonstrate correlation method for estimation of the electrical noise part correlated to the optical fluctuations, what is related to the defect presence in the LD active layer. Also changes of other characteristics at the lasing threshold are presented: electrical derivative, conductance, and capacitance, providing more information about processes in laser diodes and helping to identify threshold correctly.