Photonic crystal directional coupler for all-optical switching,tunable multi/demultiplexing and beam splitting applications

In this paper, we introduce a new configuration based on the combination of photonic crystal directional coupler and nonlinear electromagnetically induced transparency (EIT) phenomenon in solid-state materials. The proposed structure has the abilities of switching, tunable multi/demultiplexing and tunable power beam splitting. These applications are attainable in the same structure by modulating the refractive index of special regions via EIT effect. This effect causes a high reduction in the required optical control power for the desired refractive index change, compared to the other nonlinear methods. Band structure calculations and simulations of optical field propagation through the device are done by plane wave expansion and finite difference time domain methods, respectively. In the switching mechanism, extinction ratios of 11.38?dB in the linear regime (with the control signal being off) and 26.63?dB in the nonlinear regime (with the presence of control signal) are achievable. Also, the proposed structure operates as a two-channel multi/demultiplexer for wavelengths of 1550?nm and 1480?nm in the linear regime, for wavelengths of 1550?nm and 1600?nm in both linear and nonlinear regimes, and for wavelengths of 1480?nm and 1600?nm in the nonlinear regime (the nonlinear regime is the same as the nonlinear regime for the switching). Since different refractive indices are obtained by changing the power of the control signal, the wavelengths for multi/demultiplexer operation can be tunable. Finally, simulation results show that the suggested structure can operate as a tunable power beam splitter at the wavelength of 1550?nm.