The term Photonic Chrystal Fibers (PCF) describes a range of different fiber types including Hollow Core fibers, Polarization-maintaining Large-Mode-Area fibers (LMA-PM), singlemode Large-Mode-Area fibers (LMA) and highly nonlinear or highly dispersive photonic crystal fibers, all different in fiber specifications and suitable for a wide range of applications.
Photonic crystal fibers optimized for singlemode operation have a wide spectral range combined with a relatively large mode field diameter, and thus being able to transmit high optical powers. They are made from fused silica and thus resistant to solarization effects. The mode field diameter for LMA-fibers is almost wavelength-independent, whereas the numerical aperture NA depends on the wavelength. The specific arrangement of holes in the photonic chrystal cladding however leads to a beam profile with a hexagonal shape that only approximates a Gaussian shape.