Measurement of the Linewidth Enhancement Factor of Semiconductor Lasers based on the Optical Feedback Self-Mixing Effect

A new method for the measurement of the linewidth
enhancement factor of semiconductor lasers is presented, based
on the interferometric self-mixing effect. It is a fast and easy to
perform method that does not require radio frequency nor optical
spectrum measurements. A small fraction of the emitted light is
backreflected into the laser cavity by a remote target driven by a
sine waveform. The mixing of the returned and the lasing fields
generates a modulation of the optical output power in the form
of an interferometric waveform, with a shape that depends on the
optical feedback strength and the linewidth enhancement factor
, according to the well-known Lang–Kobayashi theory.We show
that the value of can be retrieved from a simple measurement of
two characteristic time intervals of the interferometric waveform.
Experimental results obtained on different laser diodes show an
accuracy of 6.5%.