Resonant splitting in periodic T-shaped photonic waveguides

Resonant splitting phenomena of photons in periodic T-shaped waveguide structure are investigated by the Green’s function method. An interesting resonant phenomenon is found in the transmission spectra. When the T-shaped structure contains n constrictions, there are (n − 1)-fold resonant splitting peaks in the low frequency region. The peaks are induced by low quasi-bound states in which photons are intensively localized in the stubs, while (n − 2)-fold resonant splitting occurs in the high frequency region. These peaks are induced by the high quasi-bound states where the photons are mainly localized in constrictions rather than in stubs. To this kind of quasi-bound state, the stub acts as a potential barrier rather than a well, which is the inverse of the case of the low quasi-bound states corresponding to the (n − 1)-fold splitting peaks. These resonant peaks can be modulated by adjusting the periodic number and geometry of the waveguide structures. The results can be used to develop optical switching devices, tunable filters, and coupled waveguides.