Optical losses in single-mode laser diodes

• Optical gain is measured in single-mode devices by controlled change in optical losses.
• The method is first applies to an ITLA and then to a DFB laser.
• Degradation of an ITLA is explained by means of the new method.
• Models are discussed dealing with threshold current.

The analysis of the effects of controlled optical losses in an external cavity Integrated Tunable Laser Assembly (ITLA) first leads to identify the failing element in a degraded identical device, and then allows to decode the effects of FIB-induced modifications on a DFB laser diode. The results open the way to much general considerations about fundamentals on laser diode characteristics, first on the physical meaning of the quantum efficiency, and then on the validation or rejection of two different models for the current threshold.