In this work, we discuss a novel architecture for an all-fiber linearly polarized counter-pumped linear amplifier utilizing an 85 μm core diameter rod fiber. Signal light is launched directly into the core region of the rod fiber with high coupling efficiency via a monolithic Mode-Field Adapter (MFA) splice. The free-space coupling optics and alignment for counter-pumping the amplifier are contained and fixed in a small, ruggedized packaging. Both the monolithic MFA splice and fixed free-space optics lock the signal and pump coupling efficiencies, allowing the device to be handled as if it were entirely monolithic. Over 18 dB of gain was achieved during power testing as a single-stage linear amplifier. Methodologies for advancing this architecture into a multistage linear amplifier to achieve higher peak and average powers are discussed. Simulations and models are used to define the signal power, pump power, gain fiber geometries, and gain stage lengths required to achieve 1 mJ pulse energies in 1 ns pulse durations, as well as predict the resulting B-integral, Amplified Spontaneous Emission (ASE) levels, and unabsorbed pump power. The feasibility of realizing such an amplifier architecture is then discussed as a conclusion.
We demonstrate that the PM 56/400 Yb tapered fiber achieves a good combination of large mode field diameter and beam quality for use in a pulsed, monolithic fiber amplifier. We evaluate this fiber over a wide test regime to determine its viability when compared to other amplifier fibers. Our focus is achieving as much energy, peak power, and average power as possible while remaining conservative to protect the fiber long-term. The fiber is tested using our Counter-Pumped Tapered Endcap (CPTEC) design that retains the benefits of counter-pumping without the drawbacks of free-space coupling.
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.
We report on the progress towards the development and performance of Photonic Crystal Fiber (PCF) based multi-kW
fiber amplifiers that are both narrow linewidth and have near diffraction limited beam quality for government and
industrial applications that are both reliable and highly affordable. These amplifiers based on the foundation of Photonic
Crystal Fibers along with a novel multi fiber-coupled laser diode stack and a monolithic 6+ l×l large fiber pump/signal
multiplexer. The pixilated nature of the PCF fabrication process allows for the inclusion of precise index of refraction
control so designs to control SBS, prevent modal instabilities and integrate large quantities of pump light can be realized,
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. A completely
monolithic amplifier utilizing these components has been demonstrated at 967W of output power at 1085nm.
There is demand for improved deep-space satellite communications links with increased data rates to accommodate
new sensor technologies and increased sensor payloads on spacecraft. It is imperative that new solutions be compact
in size, light in weight, be high speed, and highly power efficient. Optical links offer potential improvements in
power, size and weight due to a substantially narrower beam and smaller components. Solutions using fiber-laser
transmitter master-oscillator power-amplifiers (MOPA) have been investigated previously, but methods for improving
the system power efficiency are needed. In this paper we will present recent results for a 1.5um fiber MOPAs for
deep-space communications. A high-power, broad linewidth 1550 nm seed laser is combined with 3 stages of
amplification. Each of these stages is partially designed based on the availability of the various components An
amplifier operating at 1532 nm in principle has the advantage of commercial off-the-shelf components with
demonstrated reliability though the availability of high power broad area pump diodes at 1532nm with good efficiency
is limited. The final power amplifier stage was constructed using both step index fiber (SIF) and photonic crystal fiber
(PCF).
We report on the development and performance of a key components that enable the construction of multi-kW fiber
amplifiers for government and industrial applications that are both reliable and highly affordable. The usefulness of these
components span the range from single frequency near diffraction limited kW class fiber lasers to multimode wide
linewidth fiber lasers for welding and cutting applications. The key components for these amplifiers are 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 20/440 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 500
μm 0.55 NA core of the PCF fiber with a measured pump combining efficiency of 92% with zero 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 90% while
maintaining polarization with a measured PER of 20 dB. We report the signal coupling efficiency and power handling
capability as well.
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