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 C2 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 λ = 1550 nm, high polarization extinction ratios with ∼26 dB (for TE polarization) and ∼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 θ = [40°–55°]. 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.