| 摘要 |
PURPOSE:To suppress the incidence of an error floor to be small in a code error rate versus a receiving sensitivity characteristic after the transmission in a long fiber by a method wherein slope efficiencies of an optical output versus a current characteristic at the injection of respective specific electric currents are compared and screened. CONSTITUTION:There exists a strong correlation between the stability against returned light and an optical output versus an injection current characteristic when a transmission characteristic of individual elements is tested; it is possible to make a selection on the basis of the optical output versus the injection characteristic; and an element is screened as a good product in the following case: a slope efficiency of the optical output versus the current characteristic at the injection of an electric current at 1.2 times the oscillation threshold value of a distributed feedback semiconductor laser having a phase shift structure in a diffraction grating adjacent to an active layer is larger by 5% or higher as compared with a slope efficiency near the oscillation threshold value. Thereby, it is possible to suppress that an error floor is caused in a code error rate versus a receiving sensitivity characteristic after the transmission in a long fiber. |
