Frequency conversion through spontaneous degenerate four wave mixing (FWM) is investigated in large mode area hybrid photonic crystal fibers. Different FWM processes are observed, phasematching between fiber modes of orthogonal polarization, intermodal phasematching across bandgaps, and intramodal phasematching within the same transmission band as the one containing the pump laser. Furthermore first and second order Ra- man scattering is observed. The interplay between the different FWM processes and Raman scattering are investigated.
We report on the development and performance of a fully monolithic PCF amplifier that has achieved over 400 W with near diffraction limited beam quality with an approximately 1GHz phase modulated input. The key components for these amplifiers are an advanced PCF fiber design that combines segmented acoustically tailored (SAT) fiber that is gain tailored, a novel multi fiber-coupled laser diode stack and a monolithic 6+1x1 large fiber pump/signal multiplexer. The precisely aligned 2-D laser diode emitter array found in laser diode stacks is utilized by way of a simple in-line imaging process with no mirror reflections to process a 2-D array of 380-450 elements into 3 400/440μm 0.22NA pump delivery fibers. The fiber combiner is an etched air taper design that transforms low numerical aperture (NA), large diameter pump radiation into a high NA, small diameter format for pump injection into an air-clad large mode area PCF, while maintaining a constant core size through the taper for efficient signal coupling and throughput. The fiber combiner has 6 400/440/0.22 core/clad/NA pump delivery fibers and a 25/440 PM step-index signal delivery fiber on the input side and a 40/525 PM undoped PCF on the output side. The etched air taper transforms the six 400/440 μm 0.22 NA pump fibers to the 525 μm 0.55 NA core of the PCF fiber with a measured pump combining efficiency of over 95% with a low brightness drop. The combiner also operates as a stepwise mode converter via a 30 μm intermediate core region in the combiner between the 20 μm core of the input fiber and the 40 μm fiber core of the PCF with a measured signal efficiency of 60% to 70% while maintaining polarization with a measured PER of 20 dB. These devices were integrated in to a monolithic fiber amplifier with high efficiency and near diffraction limited beam quality.
1178 nm single-frequency amplification by Yb-doped photonic bandgap fiber has been demonstrated. 24.6 W
output was obtained without stimulated Brillouin scattering. 1.8 dB suppression of Brillouin gain by an acoustic
antiguiding effect has been found in the low-index core antiresonant reflecting optical waveguide.
High-power fiber lasers and amplifiers have gained tremendous momentum in the last 5 years. Many of the traditional manufacturers of gas and solid-state lasers are now pursuing the fiber-based systems, which are displacing the conventional technology in many areas. High-power fiber laser systems require reliable fibers with large cores, stable mode quality, 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 100 μm single-mode polarization-maintaining rod-type fiber capable of amplifying to megawatt 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.
Ytterbium-doped photonic-bandgap fiber sources operating at the long-wavelength edge of the ytterbium gain band are
being investigated for high power amplification. Artificial shaping of the gain spectrum by the characteristic distributed
filtering effect of the photonic bandgap enables power scaling free of amplified spontaneous emission. As high as 167 W
power and 16 dB saturated gain at 1178 nm have been demonstrated. Single-pass frequency doubling to 14.5W 589nm
light was also demonstrated with 34% conversion efficiency.
We demonstrate electrical tunability of a fiber laser using a liquid crystal photonic bandgap fiber. Tuning of the laser is
achieved by combining the wavelength filtering effect of a liquid crystal photonic bandgap fiber device with an
ytterbium-doped photonic crystal fiber. We fabricate an all-spliced laser cavity based on a liquid crystal photonic
bandgap fiber mounted on a silicon assembly, a pump/signal combiner with single-mode signal feed-through and an
ytterbium-doped photonic crystal fiber. The laser cavity produces a single-mode output and is tuned in the range 1040-
1065 nm by applying an electric field to the silicon assembly.
We demonstrate suppression of amplified spontaneous emission at the conventional ytterbium gain wavelengths around
1030 nm in a cladding-pumped polarization-maintaining ytterbium-doped solid core 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.
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 M<sup>2</sup> of less than 1.1. Finally, we briefly touch upon the subject of photo darkening and its origin.