No abstract

We report on an easy-to-evaluate expression for the prediction of the bend-loss for a large mode area photonic crystal fiber (PCF) with a triangular air-hole lattice. The expression is based on a recently proposed formulation of the V-parameter for a PCF and contains no free parameters. The validity of the expression is verified experimentally for varying fiber parameters as well as bend radius. The typical deviation between the position of the measured and the predicted bend loss edge is within measurement uncertainty.

We numerically calculate the equivalent mode-field radius of the fundamental mode in a photonic crystal fiber (PCF) and show that this is a function of the V parameter only and not the relative hole size. This dependence is similar to what is found for graded-index standard fibers, and we furthermore show that the relation for the PCF can be excellently approximated with the same general mathematical expression. This is to our knowledge the first semianalytical description of the mode-field radius of a PCF.

We demonstrate suppression of amplified spontaneous emission at the conventional ytterbium gain wavelengths around 1030 nm in a cladding-pumped polarization-maintaining ytterbium-doped all-solid photonic crystal fibre. The fibre works through combined index and bandgap guiding. Furthermore, we show that the peak of the amplified spontaneous emission can be shifted towards longer wavelengths by rescaling the fibre dimensions. Thereby one can obtain lasing or amplification at longer wavelengths (1100 nm - 1200 nm) as the amount of amplification in the fibre is shown to scale with the power of the amplified spontaneous emission.