Investigation On Polarization Mode Coupling Of Photonic Crystals

Mode coupling is an interesting and important characteristic of Photonic Crystals (PCs). Polarization mode coupling loss is a main part of loss of Photonic Crystals Waveguide (PCWG), and it could be reduced by optimizing PCWG. Mode coupling in 2 dimensional (2D) PCs introduced by kz wave-vector is also an interesting phenomenon. In this paper, polarization mode coupling loss in 2D PCWG is studied, and mode coupling in 2D PCs introduced by kz wave-vector is also investigated.Main points in this paper: (1) The refractive index contrast is reduced by inserting small rods/holes into 2D PCs. For air holes PCs with square lattice, the refractive index contrast is reduced to 2.20, which is even smaller than that of triangular lattice. (2) Mode coupling loss in 2D PCWG is studied, and the physical mechanism is presented. Mode coupling loss is resulted by the nonorthogonality of polarization modes, which are approximately classified because of the asymmetry in the vertical direction. (3)A method of analyzing and calculating mode coupling loss is established, and design of PCWG is directed. (4) Mode coupling in 2D PCs introduced by kz wave-vector is investigated.