High-power broad-area diode lasers are the most efficient light sources, with 90-μm stripe GaAs-based 940-980 nm single emitters delivering > 10 W optical output at a power conversion efficiency ηE(10 W) > 65%. A review of efforts to increase ηE is presented here and we show that for well-optimized structures, the residual losses are dominated by the p -side waveguide and nonideal internal quantum efficiency ηi . The challenge in measuring efficiency to sufficient precision is also discussed. We show that ηE can most directly be improved using low heat sink temperature THS with ηE(10 W) reaching > 70% at THS = -50 °C. In contrast, increases in ηE at THS = 25 °C require improvements in both material quality and design, with growth studies targeting increased ηi and reduced threshold current and design studies seeking to mitigate the impact of the p-side waveguide. “Extreme, double asymmetric” (EDAS) designs are shown to substantially reduce p-side losses, at the penalty of increased threshold current. The benefit of EDAS designs is shown here using diode lasers with 30-μm stripes, (in development as high beam quality sources for material processing). Efficiency increases of ~ 10% relative to conventional designs are demonstrated at high powers.

Efficient High-Power Laser Diodes

We present a cladding-pumped single-frequency, single-mode erbium:ytterbium codoped fiber master-oscillator power amplifier source generating up to 151 W of continuous-wave output power at 1563 nm with 33% slope efficiency and 20 dB gain. This source was also tunable and had a stable operation range of 1546to1566 nm at an output power level in excess of 125 W. The doped fiber exploited a large-core design for improved power handling and mitigation of stimulated Brillouin scattering. There was no sign of having stimulated Brillouin scattering even at the highest power. Despite a large core (V=12), the output beam was nearly diffraction limited (M2=1.1). The source showed slight rollover at over 100 W of output power because of the onset of emission from ytterbium, centered at 1060 nm.

/pdf/high-power-tunable-single-frequency-single-mode-erbium-40bcbcrd6m.pdf

High-power tunable single-frequency single-mode erbium:ytterbium codoped large-core fiber master-oscillator power amplifier source

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.

/pdf/airclad-fiber-laser-technology-6d1kjmxxau.pdf

Airclad fiber laser technology

We present record-breaking experimental data on high power transmission through novel 7X1 and 19X1 multimode
combiners based on Photonic Crystal Fiber technology. Both combiners are monolithic, have losses of ~0.2 dB, show
very high thermal robustness and can handle record high optical powers. We have transmitted 100 W through the 7X1
and 310 W through the 19X1 combiner without evidence of any degradation or critical heating. The powers were limited
only by available pump power.
The combiners are based on Air-clad technology, where a ring of air-holes running along the length of the device provide
guiding for the light. This Air-clad offers three major advantages for the device: 1: It is well suited for high optical
powers as no polymer coating gets into contact with the light; 2: it is much easier to package as mechanical contact can
be made anywhere on the device without risk of optical performance penalty; 3: the Numerical Aperture of the light can
be increased beyond the limits imposed by polymer coatings.
The presented pump combiners are especially well suited for high power fiber lasers, since such combiners can be
spliced directly onto the active fiber, thereby enabling a robust, stabile laser solution with excellent efficiency and beam
quality.

High-power PCF-based pump combiners

An optimized beam transformation system (BTS) is proposed to improve the beam quality of laser-diode bars. Through this optimized design, the deterioration of beam quality after the BTS can be significantly reduced. Both the simulation and experimental results demonstrate that the optimized system enables the beam quality of a mini-bar (9 emitters) approximately equal to 5.0 mm × 3.6 mrad in the fast-axis and slow-axis. After beam shaping by the optimized BTS, the laser-diode beam can be coupled into a 100 μm core, 0.15 numerical aperture (NA) fiber with an output power of over 100 W and an electric-optical efficiency of 46.8%.

Optimization of beam transformation system for laser-diode bars

Fiber lasers are pumped by fibercoupled, multimode single chip devices at 915nm. That’s what everybody assumes when asked for the type of fiber laser pumps and it was like this for many years.
Coming up as an amplifier for telecom applications, the amount of pump power needed was in the range of several watts. Highest pump powers for a limited market entered the ten watts range. This is a range of power that can be covered by highly reliable multimode chips, that have to survive up to 25 years, e.g. in submarine applications. With fiber lasers entering the power range and the application fields of rod and thin disc lasers, the amount of pump power needed raised into the area of several hundred watts. In this area of pump power, usually bar based pumps are used. This is due to the much higher cost pressure of the industrial customers compared to telecom customers. We expect more then 70% of all industrial systems to be pumped by diode laser bars. Predictions that bar based pumps survive for just a thousand hours in cw-operation and fractions of this if pulsed are wrong. Bar based pumps have to perform on full power for 10.000h on Micro channel heat sinks and 20.000h on passive heatsinks in industrial applications, and they do.
We will show a variety of data, “real” long time tests and statistics from the JENOPTIK Laserdiode as well as data of thousands of bars in the field, showing that bar based pumps are not just well suitable for industrial applications on high power levels, but even showing benefits compared to chip based pumps. And it’s reasonable, that the same objectives of cost effectiveness, power and lifetime apply as well to thin disc, rod and slab lasers as to fiber lasers. Due to the pumping of fiber lasers, examples will be shown, how to utilize bars for high brightness fiber coupling. In this area, the automation is on its way to reduce the costs on the fibercoupling, similar to what had been done in the single chip business. All these efforts are part of the JENOPTIK Laserdiode’s LongLifeTechnologie.

High-power diode laser bars as pump sources for fiber lasers and amplifiers (Invited Paper)

Lasers for marking, direct application laser systems as well as high power solid state lasers require highly reliable, high
efficient and low cost laser diodes. Especially fiber lasers and direct diode systems have additionally the need for high
brightness. For a very long time either single emitter solutions with low brightness and costs or beam shaped bar
solutions with high brightness and high costs served those needs. Since roughly 2 years multiple single emitter solution
are more and more penetrating the market showing a high potential for serving all needs of a broad customer base.
Based on the 50W product introduced by the middle of 2009 we would like to show the design which is based on
qualified and highly stable single emitters.

Roadmap to low cost, high brightness diode laser power out of the fiber

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High-power diode laser bars as pump sources for fiber lasers and amplifiers (Invited Paper)

Roadmap to low cost, high brightness diode laser power out of the fiber