The Modern Directed Energy HEL is nearly entirely based on the combined fiber laser array. These lasers are compact, rugged, low SWAP with high beam performance. Currently at 2-3kW of near diffraction limited output, they are imminently scalable from 10kW CUAS lasers to 1MW strategic lasers. OEI has been utilizing its decades long expertise in fiber glass processing to create lasers that have even higher levels of performance while greatly reducing the structural overhead currently required for laser and beam control. In this talk OEI will survey the current state of the art in DE Laser Fiber laser glass processing in areas including cleaving, tapering, etching and splicing, and thermal management and mode stripping well as future developments in combiners, mode adapters, and -65dB kW tap couplers. System enhancements such as monolithic fiber laser control, advanced output structures, as well as fiber array passive alignment, and novel structures such as the Counter Pumped Tapered End Cap (CPTEC) and the Fly’s Eye Fiber Laser Array (FEFLA) will also be discussed.
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.
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 report development of 85µm core Yb-doped and Ge-doped chirally-coupled-core (CCC) fibers, and their integration via fusion-splicing into an all-fiber optical amplifier system. This system, consisting of a CCC fiber amplifier and a 6+1 fusion-spliced signal-pump-combiner with a passive CCC fiber feed-through produces robust single mode output (diffraction-limited) in a counter-pumped configuration with passive-fiber leads as short as ~30cm. The Yb-doped 85µm core CCC fiber amplifiers had produced ~10mJ energy pulses at close to ~100W of average power. This achieved performance and monolithic all-fiber integration are required for compact and robust coherently-combined laser array drivers of laser plasma accelerators.
We report on the performance of a prototype pump combiner for use with thulium-doped photonic crystal fiber (PCF). This platform is attractive for “all-fiber” high energy and high peak power laser sources at 2 μm. We will report on the performance of this integrated amplifier in comparison to free space amplification in Tm:PCF. In particular, we carefully look for spectral/temporal modulation resulting from multimode interference between fundamental and higher order transverse modes in the amplifier to evaluate this for ultrashort chirped pulse amplification. The slope efficiency for the all-fiber amplifier is 22.1 %, indicating the need for further improvement. However, an M2 < 1.07 demonstrates excellent beam quality, as well as amplified polarization extinction ratios of ~25 dB.
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 performance of monolithic, polarization maintaining, Er-doped photonic crystal fibers (PCF) and
amplifiers operating in the eye-safer wavelength regime from 1.55-1.6 um. As part of this effort, we have developed
novel 6x1+1 pump/signal combiners for air-clad photonic crystal fibers with six 0.22 NA, 200/220 um pump input fibers
and a 25/250 PM signal fiber that allow efficient pump and signal coupling to the air-clad Er-doped PCF. These etched
air taper combiners have been demonstrated at the kilowatt level under 976 nm pumping and perform an efficient
brightness transformation from 0.19 NA, 1532 nm fiber coupled diode pumps into the 0.6 NA air-clad Er-doped PCF
with a measured pump throughput efficiency of 88-92% and a signal throughput of 65-80% with a PER of <18 dB.
These novel combiners have been efficiently spliced to 40 um core, 200 um pump cladding Er-doped PCFs providing
high efficiency resonantly pumped, monolithic, eye-safer PCF fiber lasers and amplifiers. Using grating stabilized 1532
nm pump diodes, our current experiments have demonstrated single transverse mode operation of both monolithic eyesafer
PCF lasers and amplifiers at the multi-Watt level with slope efficiencies of over 55%.
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.
Fiber lasers create unique opportunities for creating high energy lasers. The distributed gain and
heat deposition, and the flexible resonator provide the means for scaling to high powers. In
addition and perhaps more valuable is the idea that fiber lasers allow the creation of an extensible
architecture: an architecture where the individual components can be researched, designed,
improved and replaced independently. In order to create sources at power levels over 3kW in
volumes less than .01m3/kW, weighing less than 2kg/kW at costs under $1 per Watt of fiber
laser output, serious consideration first needs to be given to the underlying architecture of choice.
In this presentation, several architectural constraints along with competing approaches will be
presented. Preliminary results from high brightness fiber coupling, and fiber combiner designs
and experiments will be presented.
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 methods for improving the wall-plug efficiency
of fiber MOPAs for deep-space communications. A high-power, wavelength-stabilized, 1550 nm seed laser with an
external modulator is used to reduce the number of amplifier stages. In addition, resonant pumping in the 1430 to
1530 nm band improves pump absorption and, hence, wall-plug efficiency. A first-stage amplifier is used in order to
maximize extraction efficiency at high gain. The design targets a wall plug efficiency of 20% with more than 1 kW of
peak power per pulse and over 10 W of average power. An amplifier operating at 1532 nm also has the advantage of
commercial off-the-shelf components with demonstrated reliability.
We report on the performance of a monolithic 6+1X1 fiber pump signal multiplexer for use in fiber amplifiers.
The key component of this coupler design is an etched taper that transforms the low-numerical aperture large
diameter pump radiation into a high numerical aperture small diamter format for injection into the pump
cladding of an air-clad fiber while maintaining a constant refractive index profile in the core for efficient signal
coupling. This taper was then fused onto the 6+1 fiber bundle at the large end and to the air-clad large mode
area polarization maintaining photonic crystal fiber at the small end. We employed 6 pump delivery fibers in
a 200/220/0.22 core/clad/NA format and a 25/250 polarization maintaining step index signal delivery fiber for
the bundle. The large end of the taper had a cladding diameter of 650 μm while the small end had a cladding
diameter of 300 μm to match the pump cladding diameter of the PCF which was 314 μm. The core within
the taper had a constant diameter of 40 μm and NA of 0.07 achieved through a step index profile. The mode
field diameter of the PCF was 54 μm. Signal coupling efficiency at 1550 nm was measured to be 90% with a
polarization extinction ratio > 20dB while pump coupling efficiency was measured to be 87% at 1532nm. The
low pump coupling efficiency was found to be due to pump delivery fibers that had a numerical aperture of 0.24,
higher than the specification of 0.22. A simple calculation shows that with 0.22 NA pump fibers, the pump
coupling efficiency would increase to 94%.
Fiber lasers create unique opportunities for creating high energy lasers. The distributed gain and heat deposition, and the flexible resonator provide the means for scaling to high powers. In addition and perhaps more valuable is the idea that fiber lasers allow the creation of an extensible architecture: an architecture where the individual components can be researched, designed, improved and replaced independently. In order to create sources at power levels over 10kW in volumes less than 1 cu. ft. weighing less than 50lbs at costs under $1 per Watt of laser output. Serious consideration first needs to be given to the underlying architecture of choice. In this presentation, several architectural constraints along with competing approaches will be presented. Preliminary results from high brightness fiber coupling designs and simulations will also be discussed.
The advent of digital technology in HFC networks has opened up a myriad of opportunities for MSOs. The introduction of these advanced services comes at a cost: namely, the need for increased capacity; and especially increased reusable bandwidth. In HFC networks all services are ostensibly broadcast: the prime difference between services being the footprint over which these services are broadcast. Channel lineups for broadcast video services typically cover the largest are. Advertising zones are typically second, usually on the order of a typical 20K home hub. For initial penetrations for high speed data services such as cable modems, a typical hub site will be divided into several sectors using a single 6 MHz channel. Telephony services are broadcast over the smallest area, typically a 6 MHz channel for each node. Naturally as penetration of these services increase, the broadcast area for each will also decrease.
The inherent low loss, wide instantaneous bandwidth, and light weight over large distances of the optical fiber make it an attractive option for a coaxial-based link system. Fiber optic links have been demonstrated for operation at rf frequency and into the mm-wave range within the last few years. In order to extend the dynamic range even more, either the modulation approach has to be modified or an rf linearization technique has to be used that will have an impact on the instantaneous frequency bandwidth. This papers describes a novel approach for extending the dynamic range of a fiber otic link by utilizing a double-sideband, suppressed-carrier modulation approach in conjunction with an optical amplifier. The system will be an inherently wide bandwidth system limited at this time to operation at 1550 nm due to the current availability of optical amplifiers. Before describing the linearized system, a brief discussion of the operational dynamic range as related to externally modulated systems is described.
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