Hollow core photonic bandgap fibers guide light in a hollow  core surrounded by a microstructured cladding formed by a  periodic arrangement of air holes in silica. 
Since only a small fraction of light propagates in glass, the effect of material nonlinearities is significantly reduced. 
Applications include power delivery, pulse shaping and compression, sensors and non-linear optics.
・>95% of optical power located in air 
・Gaussian-like fundamental mode 
・Can be filled with gas 
・Low bend loss down to few mm bend radius 
・Fresnel reflection to air at the end faces <10e-4
  ・Undoped silica for good temperature stability







