Waveguiding properties of photonic crystal fiber

The out-of plane propagating waves in glass-air-hole periodical photonic crystal demonstrate the band gaps when its effective index is less than unity. This leads to guiding of high-order modes of index-guiding photonic crystal fiber below their cut-off due to reflection from the periodical cladding at the band gap frequencies. These guiding phenomena were investigated using plane-wave calculation of band gap diagram of periodical cladding, and dispersion curves of eigenmodes of photonic crystal fiber. Finite-element calculations of field patterns in the photonic crystal fiber demonstrate these guiding phenomena.