Comparison of the tapered photonic crystal fiber waveguide couplers and conventional couplers

The photonic crystal coupler and conventional step-index coupler are theoretically investigated. The photonic crystal coupler has been made by the stepless tapering of the photonic-crystal holey fiber and the conventional step-index coupler - by the stepless tapering of the conventional fiber. The photonic crystal couplers are characterizing by material refractive index changing in a spatial direction along the wave propagation direction. In our investigation an effective refractive index model of two-dimensional photonic crystal was used. This model allows to analyze the waveguide structures, which work on the effective index waveguiding in a defect of the photonic crystal. The optical field in photonic crystal couplers and conventional couplers was investigated and losses and mode composition of both types of the couplers were calculated.