Abnormal transient wavelength-chirping dynamics in quantum-well-box distributed feedback lasers

ring. Referring to Fig. l a , in region 1 no guided mode exists; in region 2 a guided mode can exist in the disk; in region 3 guided modes can exist in both the diskand the ring (see Fig. lb), and thus a resonant coupling may occur; in region 4 guided modes can exist only in the ring. As the radii of the disk and ring decreases, for achieving resonant coupling, the ring should be thinner and closer to the disk, which results in a strong coupling. Under a certain radius, no coupling can exist at all. For disk radius smaller than about 0.4 * A, weak coupling is impossible. This also implies that a mode with less than 10 azimuthal lobes cannot be weakly coupled to a surrounding ring. For a given radius, the number of rings that can be coupled is limited. Figure 2 demonstrates the weak-resonantCWF18 Fig. 3 Experimental photographs of whispering gallery mode in a disk (a), a ring (b) and a system of a disk and a ring.