With the finite element method (FEM)，the Fano resonances（FRs）and linewidth compression in a silver nanorod quadrumer (SNQM) system formed from four silver nanorods is investigated. The SNQM is made up of two dimers, one composed by two identical and parallel silver nanorods that can be regarded as a resonant cavity (RC), the other is inserted in the DR composed by two same silver nanorods oriented in the same direction which can be taken as a dipole antenna (DA). The results show that the distinct FRs are observed in the transmission spectra of the SNQM，which derives from the interference between the super-radiant mode and the sub-radiant mode that caused by the interaction of the surface plasmons of the RC and DA. FRs can be tuned in both resonance wavelength and modulation depth by adjusting the structure parameters. Meanwhile, under the appropriate structure parameters, the narrow linewidth radiation of the DA can be enhanced in the RC.

silver nanorod; quadrumer; surface plasmons; Fano resonances; linewidth compression