Measurements of dynamic linewidth enhancement factor and damping rate for distributed-feedback lasers

摘要

amic linewidth enhancement factor, $alpha@, and damping rate, $Gamma@, for distributed feedback (DFB) lasers are obtained at various bias levels by measuring the frequency modulation and amplitude modulation indices of the lasers simultaneously. The $alpha@-value of a DFB lasers is generally reduced with increasing output power except at low bias, and the $Gamma@-value typically increases with output power. The measured results show that ninety percent of the 1.3-$mu@m capped-mesa buried heterostructure DFB lasers have $alpha@-values in the range 4 to 7 and $Gamma@-values below 4 $MUL 10$+10$/ s$+$MIN@1$/. The 1.3- $mu@m lasers have smaller damping rates than the 1.5-$mu@m lasers of the same DFB laser structure. Compared with buried heterostructure DFB lasers, multiquantum well (MQW) DFB lasers exhibit a much smaller $alpha@-value and a larger damping rate. For both unstrained and strained 1.5-$mu@m MQW-DFB lasers, $alpha@-values as low as 1.5 can be easily realized for these lasers at high output power ($GREQ 10 mW).