Feasibility study on the application of the quantum disk to the gain-coupled distributed feedback laser

This numerical study investigated the possibility of using quantum disks in a gain-coupled distributed feedback (DFB) laser, specifically whether the laser would oscillate when the number of electrons in a disk (N_th) is less than the maximum possible number of electrons in the disk (i.e., oscillate at a threshold material gain (g_th) less than the maximum peak material gain for each quantum disk). The influences of the disk diameter and thickness, the number of disks stacked vertically in a layer (N_st), the device length, the period perpendicular to the light propagation direction, and facet reflectivity on the g_th, the threshold current density (J_th), and the normalized gain-coupling coefficient (K_gL) were also examined. When N_st is increased, g_th decreases to less than the value estimated when assuming that the product of g_th and N_st is constant. Although closely spaced disks are useful for reducing g_th , there is an optimum disk distribution minimizing J_th, and this distribution depends on the parameters described above. The J _th also depends on the disk size and is smallest when the diameter is 6 nm. The magnitude of K_gL is about 0.76 and is independent of the height of the gain grating (i.e., N_st), but it can be controlled by adjusting the disk diameter and the facet reflectivity