Modal content analysis of hollow core Kagome fibers

We report on quantitative modal content measurements by S2 measurements in a Kagome type hollow core fiber depending on bending and in-coupling optimization. The higher order mode content could not be completely suppressed impacting important applications

Detailed investigations on thermal mode instabilities in LMA Yb-doped fibers

We present our investigations on modal instabilities using a commercial LMA fiber with 25 µm core and 400 µm cladding. The transversal mode instability (TMI) threshold is measured for different seed wavelengths and bending diameters in a systematic way. Additionally, in-situ temperature measurements up to the TMI threshold allowed measuring the longitudinal resolved thermal load and, thereby, fixing parameters for simulations that match experimental values. In conclusion, we derive driving parameters for TMI and found that photodarkening has a negligible impact on TMI in this fiber

All-solution doping technique for high power fiber lasers - refractive index influence in the vicinity of Al:P = 1:1

A novel and simple solution doping technique is used to explore the refractive index behavior of Al,P-doped SiO2 in the vicinity of the Al:P-ratio of 1:1 at low doping concentrations. It is found that even if Al:P = 1:1 is matched precisely an index increase is observed. This is in contradiction to previous findings in the literature and the already sophisticated models need to be refined in this region

Measuring thermal load in fiber amplifiers in the presence of transversal mode instabilities

We report on detailed in situ distributed temperature measurements inside a high power fiber amplifier. The deducted thermal load and the transversal mode instability (TMI) threshold of a commercial large mode area fiber with 25 mu m core and 400 mu m cladding were measured at various seed wavelengths. By matching these results with detailed simulations we show that photodarkening has a negligible impact on the thermal load and, therefore, on the TMI threshold in this fiber

Modal content measurements (S2) of negative curvature hollow-core photonic crystal fibers

We present modal content measurements (S2) of two different negative curvature hollow-core photonic crystal fibers: a kagome fiber and an ice cream cone fiber. Their sensitivity towards mode matching, bending and polarization is analyzed. For the kagome fiber, a higher order mode suppression of 17dB under optimal conditions was achieved, and for the ice cream cone fiber there was a suppression of up to 42dB. Polarization turned out to be a critical parameter for good higher order mode suppression in both fibers

Modelling the refractive index behavior of Al,P-doped SiO2, fabricated by means of all-solution doping, in the vicinity of Al:P = 1:1

A novel and simple solution doping technique is used to explore the refractive index behavior of Al,P-doped SiO2 in the vicinity of the Al:P-ratio of 1:1 at low doping concentrations (0.4 up to 2.0 mol% Al2O3 and/or P2O5). It is found that even if Al:P = 1:1 is matched precisely, an index increase is observed. This is in contradiction to previous findings in the literature and the already sophisticated models need to be refined in this region. In the proposed model, an incomplete formation of AlPO4 is assumed and solves the contradiction. Furthermore, the presented model can be combined with previous literature models