Transmission of optical signals in coupled cavity resonators based on quasi-one-dimensional periodic nanobeam based structures

Recently, phononic and photonic properties have been combined into one platform that provided a new tool for controlling light and sound simultaneously. Such artificial materials are called phoXonic or optomechanical crystals.... [ view full abstract ]

Recently, phononic and photonic properties have been combined into one platform that provided a new tool for controlling light and sound simultaneously. Such artificial materials are called phoXonic or optomechanical crystals. Recently, a structure consisting of a corrugated nanobeam containing an array of holes in the middle and an array of rectangular plugs from the side was proposed. Detailed development of photonic modes and its interaction is necessary for the implementation of chip photon/phonon networks.

We study here the coupling between two silicon nanobeams with a quasi-periodic system of holes with single defects forming cavity resonances in the photonic bandgap. Using 3D-FDTD simulations, two configurations of "side-by-side" or "top-on-top" nanobeams were studied (Fig.1) by changing periodic arrays supporting mirror or scattering properties of the photonic structure for the transfer of the incoming TE-polarized wave from the first nanobeam input (red-port) to the output of the second (blue-port). Fig.2(a,b) present transmission spectra at the exit (port-blue) corresponding to a sharp transmission inside the photonic bandgap of the perfect structure that comes from a complex process including the excitation, the coupling and the transfer of the incoming wave based on the two modes localized inside the cavities (green arrows). As it follows from Fig.2(a,b) excitation/coupling/transfer process of the optical signal is more efficient in the "top-on-top" configuration and the output signal quickly falls down by increasing the air gap from 0.5μm to 1.5μm. The vertical air gap decreasing from 500nm to 300nm in the "top-on-top" configuration (Fig.2c) leads to clearly observable mode splitting on symmetric and antisymmetric states. In addition, the efficiency of the transferred splitted signal can be improved by increasing of number of perfect cells forming the Bragg mirror along unwanted directions of propagation (Fig.2d).

We show that the coupling condition between two nanobeams plays a crucial role in the process of excitation and transfer of an incident optical signal. The results of the coupling allow to the tunability of both frequency and quality factors that can be used in the design of chip based cavity optical or optomechamical devices for further applications in sensing, metrology, and quantum information science.