Design of a high efficiency wide-band 60° bend for TE polarization

In this paper, a high-efficiency 60° photonic crystal (PC) bend geometry is proposed. The corresponding PC is a two-dimensional triangular lattice of air holes in a dielectric slab. In the proposed bend structure, five additional holes are introduced in the bend. The radii of these holes are changed gradually. Hence the effect of bend discontinuity is decreased and consequently, a wide-band high efficiency bend is obtained. In this structure, the frequency bandwidth for which the transmission coefficient is greater than 0.9 covers 84% of the single-mode bandwidth of the waveguide, while for the best geometry reported in the literature this value does not exceed 56%. For numerical analysis of waveguide bends, the slab PC structure is first replaced by a two-dimensional (2D) PC with an effective refractive index and then, a 2D FDTD method is used to obtain the transmission coefficient of the bend.