Polarization splitting phenomenon of photonic crystals constructed by two-fold rotationally symmetric unit-cells

Abstract

We present an intrinsic polarization splitting characteristic of low-symmetric photonic crystals (PCs) formed by unit-cells with C-2 rotational symmetry. This behavior emerges from the polarization sensitive self-collimation effect for both transverse-magnetic (TM) and transverse-electric (TE) modes depending on the rotational orientations of the unit-cell elements. Numerical analyzes are performed in both frequency and time domains for different types of square lattice two-fold rotational symmetric PC structures. At incident wavelength of lambda = 1550 nm, high polarization extinction ratios with similar to 26 dB (for TE polarization) and similar to 22 dB (for TM polarization) are obtained with an operating bandwidth of 59 nm. Moreover, fabrication feasibilities of the designed structure are analyzed to evaluate their robustness in terms of the unit-cell orientation: for the selected PC unit-cell composition, corresponding extinction ratios for both polarizations still remain to be over 18 dB for the unit-cell rotation interval of theta = [40 degrees-55 degrees]. Taking all these advantages, two-fold rotationally symmetric PCs could be considered as an essential component in photonic integrated circuits for polarization control of light.