Polarization-independent one-way transmission of silicon annular photonic crystal heterojunctions

To realize the one-way transmission is a key point in optical integration. As a step to this goal, heterojunctions composed of two 2D square-lattice silicon annular photonic crystals are constructed and expected to realize polarization-independent optical diodes. Band structures are calculated by the plane wave expansion method, and the transmission characteristics are analyzed using the finite-different time-domain method. The directional bandgap difference causes the one-way transmission behavior, and an overlapping one-way transmission frequency range for TE and TM modes is observed. Moreover, the transmission spectra, contrast ratio and field distributions for two polarizations demonstrate polarization-independent one-way transmission. The transmission performance is further enhanced and the equal forward transmittance for two polarizations reaches 45%.