Supercontinuum generation in photonics crystal fibers (PCFs) pumped by CW lasers yields high spectral power density
and average power. However, such systems require very high pump power and long nonlinear fibers. By on/off
modulating the pump diodes of the fiber laser, the relaxation oscillations of the laser can be exploited to enhance the
broadening process. The physics behind the supercontinuum generation is investigated by sweeping the fiber length, the
zero dispersion wavelength, and the fiber nonlinearity. We show that by applying gain-switching a high average output
power of up to 30 W can be maintained and the spectral width can be improved by 90%. The zero dispersion wavelength
should be close to but below the pump wavelength to achieve the most visible light. By increasing the nonlinearity the
fiber length can be reduced from 100 m to 25 m and the efficiency of visible light generation is improved by more than
In this work we propose and demonstrate a single mode fiber design that alleviates photo darkening. The fiber design is
based on a reduced signal mode to gain material overlap which is found to reduce the induced losses of PD. For the fiber,
saturated photo darkening operation is observed after 1500 hours operation with less than 7 % reduction in slope
efficiency from 350 W output power in Yb/Al co-doped material. Power scalability up to 5 kW of the RMO fiber design
is theoretically predicted.
The model describes solitons as relativistic particles, the visible light of the continuum as the result of Cerenkov radiation
and the infrared light of the continuum as the result of material recoil. The model is applied on super continua generated
by a 1064 nm mode locked 2-10 ps pump source launched into microstructure fibres with zero dispersion wavelength in
the near infrared. The model predicts that the leading soliton of a pulse train dominates the self frequency shifting of a
train of solitons with Tera Hertz repetition rate. The mechanism is responsible for very efficient super continuum
generation in certain combinations of ps pulse sources and microstructure fibre designs.
A model description of photo darkening of ytterbium cw fiber lasers based on long term tested fiber lasers is presented.
Photo darkening of Yb/Al co-doped silica fibres is found to saturate following prolonged exposure to pump and signal
radiation. The observed slope efficiency of Al co-doping is compared with modeled slope efficiency of P co-doping.
A model description of photo darkening based on 30 characterised fibres in an un-seeded amplifier setup is presented. Photo darkening of ytterbium / aluminium and/or phosphorous co-doped silica fibres is found to saturate following prolonged exposure to pump radiation. The photo darkening is associated with non-binding oxygen at surfaces of ytterbium / aluminium clusters. The dominant colour centre at near infrared wavelengths in MCVD material is a combination of 1.9 eV (FWHM of 0.62 eV) and 2.4 eV (FWHM of 0.85 eV) absorption dependent on average phonon energy of the glass material.
High-power fiber lasers and amplifiers have gained tremendous momentum in the last five years, and many of the
traditional manufactures of gas and solid-state lasers are pursuing the attractive fiber-based systems, which are now
displacing the old technology in many areas. High-power fiber laser systems require specially designed fibers with large
cores and good power handling capabilities - requirements that are all met by the airclad fiber technology. In the present
paper we go through many of the building blocks needed to build high-power systems and we show an example of a
complete airclad laser system. We present the latest advancements within airclad fiber technology including a new 70
μm single-mode polarization-maintaining rod-type fiber capable of amplifying to MW power levels. Furthermore we
describe the novel airclad based pump combiners and their use in a completely monolithic 350 W CW fiber laser system
with an M2 of less than 1.1. Finally, we briefly touch upon the subject of photo darkening and its origin.