Bandgap modes in a coupled waveguide array

This work examines a waveguide array that consists of ten Nb₂O₅/SiO₂ double layers and supports a 0.63-μm surface wave. The deposition of a Nb₂O₅ capping layer on top of the waveguide array enables a marked increase in the wave field intensity on its surface. The efficiency of surface-wave excitation in the Kretschmann configuration can be optimised by adjusting the number of double layers. We analyse the behaviour of the Bragg mode in relation to the thickness of the layer exposed to air and the transition of this mode from the second allowed band to the first through the bandgap of the system. In addition, the conventional leaky mode converts to a surface mode and then to a guided mode.