Extended Modal Gain Measurement in DFB Laser Diodes

A practical method is proposed for complete gain measurement in distributed feedback (DFB) laser diodes. It is non-destructive and does not require any reference device. It includes the whole range of continuous gain values, from its minimum to threshold, passing through the transparency condition. The method requires a single absolute gain measurement for calibration. An example is reported for a DFB preserving Fabry-Perot multi-modes in the sub-threshold regime.