Study On Threshold And Output Characteristics Of Two-Segment DFB Semiconductor Lasers

With the development of communication services and the application of various new technologies, optical fiber communication is progressing toward great capacity, high speed, long distance and network. Accordingly, key components have been one of the most active research problems in optical fiber communication systems. Two-segment distributed feedback (DFB) semiconductor lasers can achieve tuning with single longitudinal mode in a certain wavelength range; at the same time, its superiority also includes bistablity and wavelength conversion. So it can be expected that two-segment DFB lasers will play important roles in future DWDM and multi-wavelength network.In this paper the average field is used to describe the carrier in each segment based on the carrier distribution in two-segment DFB lasers and the strict coupled wave theory is used to describe the photon density. Combined with these two methods, the threshold condition expression has been derived for the first time. Using this expression, the interrelation of the carrier density in each segment and the emission wavelength can be predicted while the laser is lasing.In the aspect of output characteristics, after applying the boundary conditions and the continue condition of two segments, the correlative dependence of average photon density in each segment has been obtained. Combining this dependence with the threshold conditions, the theory foundation is settled. On the basis of this, the effective reflective index with the variation of the carrier density is discussed. This paper also analyzed the random facet phase and the length of the cavity's influence on threshold characteristic. Especially, the wavelength tuning characteristics have been investigated in detail when one segment works as absorbed region.