Single-mode 7-cell core hollow core photonic crystal fiber with increased bandwidth

We present two low-loss 7-cell core hollow-core photonic crystal fibers (HC-PCF) with intrinsic single mode properties around 1550 nm. By reducing the number of surface modes within the bandgap these fibers can be operated close to the short wavelength bandgap edge. It is well known that by omitting a core tube in HC-PCF fabrication of a surface mode free bandgap can be achieved.

We found by experimental as well as numerical, investigation that using a core tube with a wall thickness reduced to between 60-70 % is sufficient to have a surface mode free short wavelength bandgap edge. The transmission and mode properties of the fabricated fibers are examined experimentally and compared to numerical calculations.