Numerically study of short wavelength filtering of a depressed-index core photonic crystal fiber

Short wavelength filtering based on the anti-guide property of a depressed-index core photonic crystal fiber is studied. A type of fiber filter is formed by adding a depressed-index domain to the core of an index-guiding photonic crystal fiber. The dependencies of normalized cutoff wavelength and edge steepness on the structural parameters of the fiber filter are investigated. A better quality of cutoff (lower edge steepness), a larger normalized cutoff wavelength and a wider range of normalized cutoff wavelength can be realized by increasing the relative cladding air-hole diameter. Fiber filters with the normalized cutoff wavelength (cutoff wavelength/pitch) covering ∼0.0514 to 0.5 and the edge steepness below 5% (industry standard) are demonstrated numerically. In addition, bending effect and problem caused by the existence of the photonic bandgap mode which may influence the feasibility of the filtering mechanism are considered.