Two-dimension photonic crystals coupler is studied in present paper. The photonic band gap structure and band gap map are calculated on the basis of plane wave expansion method. The finite-difference time-domain (FDTD) method is applied for analyzing transmission and coupling characteristic of photonic crystals coupler with the square lattice. The effects of coupling length and waveguide-channel space on coupling ratio are discussed. Further, the field distribution is given in this paper. The results indicate that photonic crystal can accomplish coupler function. The performance of the coupler is more sensitive to coupling length than waveguide-channel space. The phenomenon between coupler branches will disappear gradually when the waveguide-channel space increases. In terms of appropriate coupling length and waveguide-channel space, the coupler with any coupling ratio can be achieved.
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