Thermal modeling of gain competition in Yb-doped large-mode-area photonic-crystal fiber amplifier.

We propose a new model for gain competition effects in high-power fiber amplifiers, which accounts for the thermal effects of heat load on the doped core overlap of the propagating light field. The full-vectorial nature of the fiber modes is modeled by an embedded finite-element method modal solver, and the temperature profile is calculated by a simple and efficient radial heat propagation solver. The model is applied to a Yb³âº-doped LPF45 air-clad photonic-crystal fiber amplifier for coand counter-propagating pumping setups, showing gain competition in conditions of severe heat load.

Hybrid Ytterbium-doped large-mode-area photonic crystal fiber amplifier for long wavelengths.

A large-mode-area Ytterbium-doped photonic crystal fiber amplifier with build-in gain shaping is presented. The fiber cladding consists of a hexagonal lattice of air holes, where three rows are replaced with circular high-index inclusions. Seven missing air holes define the large-mode-area core. Light confinement is achieved by combined index and bandgap guiding, which allows for single-mode operation and gain shaping through distributed spectral filtering of amplified spontaneous emission. The fiber properties are ideal for amplification in the long wavelength regime of the Ytterbium gain spectrum above 1100 nm, and red shifting of the maximum gain to 1130 nm is demonstrated.

Single-mode analysis of Yb-doped double-cladding distributed spectral filtering photonic crystal fibers.

Hybrid large mode area Ytterbium-doped double-cladding photonic crystal fibers with anti-symmetric high refractive index inclusions provide efficient amplified spontaneous emission spectral filtering. Their performances have been analyzed by numerical simulations and experimental measurements. In particular, the fiber single-mode behaviour has been studied, by taking into account the fundamental and the first higher-order mode. Two approaches, the core down-doping and the reduction of the air-hole diameter in the inner cladding, have been successfully applied to reduce the higher-order mode content, regardless of the bending of the doped fiber, without significantly affecting its spectral filtering properties.