Fig. 4. Mechanism of mode selection in the axially coupled heterogeneous NW resonator system.
(A) Schematic illustration of the axially coupled heterogeneous cavities. ρ represents end-facet reflectivity of the single NW; ρeff represents effective reflectivity of the lasing cavity at the right end facet. (B) Effective reflectivity of the lasing cavity at the end facet coupled with the filter cavity, with the end-facet reflectivity of the isolated NW added as a comparison. (C) Threshold gain of the cavity modes in the active NW with and without the coupling of the passive NW. The modulated end-facet reflectivity and threshold gain demonstrate the mode selection mechanism in the axially coupled heterogeneous NW cavity system.