Fig. 1: Geometry of a Hollow Core Photonic Crystal Fiber (yellow: glass, magenta: air). The hollow core has a size of 19 unit cells of the periodic cladding.

Photonic crystal fibers, a new class of optical fibers, have impressive optical guiding and confinement properties not accessible to classical fibers. The microstructured cross-sections of these devices can be manufactured at high precision by drawing a structured and heated preform to very small diameters.

Fig. 2: Detail of an automatically generated mesh for a HCPCF.

Figure 1 shows the geometry of a typical cross section of a photonic crystal fibre with a hollow (i.e., air-filled) core. Light of high intensity can be guided with low losses over relatively large distances. Figure 2 shows a triangular discretization of the geometry (obtained with JCMgeo). Note the accurate geometrical resolution of, e.g., corner roundings and strut widths.

Fig. 3: Band structure of the cladding of the microstructured fiber.

Computing the cladding band structures (see Fig. 3) allows, e.g., to optimize the cladding structure for good light confinement in specific wavelength ranges.

Fig. 4: Intensity distribution of a guided mode in a not optimized fiber geometry.

Figure 4 shows the intensity distribution of a guided mode in a not optimized fiber geometry. For achieving optimum guiding properties, several parameters of the geometrical layout, like e.g. cladding periodicity, strut thickness, or the shape of the central hole have to be optimized. Figure 5 shows the dependence of the field confinement in the central core on a specific structural parameter.

Fig. 6: Well confined fiber mode ensures low losses.

Figure 6 shows the field distribution of a guided mode in an optimized fiber geometry. High accuracy and fast computations are extremely helpful in the optimization of such structural parameters. Figure 7 shows the same mode computed on a quarter of the cross section of the (symmetric) fiber as computational domain. The use of symmetries allows to further decrease the computational effort of PCF computations.