Parameter extraction from subthreshold spectra in cleaved gain- and index-coupled DFB LDs

Determination of device parameters in fabricated distributed-feedback (DFB) laser diodes (LDs) is very important for further optimization of the laser design and even the system design. In particular, the coupling coefficient is one of the most influential parameters, and hence it should be measured precisely. However, to date, the determination of the coupling coefficient in DFB lasers has been possible only for indexcoupled devices with antireflection-coated facets and has not been very accurate.1 Moreover, in such measurements no other parameters, such as gain and effective group index, could be derived