A new 100μm aperture, 920nm laser diode chip was developed to improve fiber coupling efficiency and reliability. These chips have been assembled into single-emitter and multi-emitter packages with 105μm diameter fiber-coupled output. The single-emitter package is rated for 12W operation, while the multi-emitter package is rated at 140W. Power conversion efficiency is 50%. Over one year of accelerated active life testing has been completed along with a suite of passive, environmental qualification tests. These pumps have been integrated into 2kW, 4kW, and 6kW fiber laser engines that demonstrate excellent brightness, efficiency, and sheet metal cutting quality and speed.
We have demonstrated a monolithic (fully fused), 1.2-kW, Yb-doped fiber laser with near-single-mode beam quality.
This laser employs a new generation of high-brightness, fiber-coupled pump sources based on spatially multiplexed
single emitters, with each pump providing 100 W at 915 nm within 0.15 NA from a standard 105/125 μm fiber. The
fiber laser is end pumped through the high-reflector FBG using a 19:1 fused-fiber pump combiner, eliminating the need
for pump/signal combiners. The output wavelength is 1080 nm, with a linewidth of < 0.5 nm FWHM. A peak power of
1.5 kW was reached in modulated operation (1-ms pulse duration) with M<sup>2</sup> < 1.2.
We report results of a spatially-multiplexed broad area laser diode platform designed for efficient pumping of fiber lasers
or direct-diode systems. Optical output power in excess of 100W from a 105μm core, 0.15NA fiber is demonstrated with
high coupling efficiency. The compact form factor and low thermal resistance enable tight packing densities needed for
kW-class fiber laser systems. Broad area laser diodes have been optimized to reduce near- and far-field performance and
prevent blooming without sacrificing other electro-optic parameters. With proper lens optimization this produces ~5%
increase in coupling / wall plug efficiency for our design. In addition to performance characteristics, an update on long
term reliability testing of 9XX nm broad area laser diode is provided that continues to show no wear out under high
acceleration. Under nominal operating conditions of 12W ex-facet power at 25C, the diode mean time to failure (MTTF)
is forecast to be ~ 480 kh.
Developers building high-power fiber lasers and diode pumped solid state lasers can receive significant benefits in thermal management and reliability by using single emitter multi-mode diodes in distributed pump architectures. This proposed distributed architecture relies on independent single emitter pump lasers and a modest level of pump redundancy. Driving the remaining diodes slightly harder componensates individual diode failures. A model of the ensemble lifetime based on module failure rates and power-scaling factors demonstrates that the distributed pump architecture requires random failure rates corresponding to better than 200,000h mean time between failure (MTBF), which meets typical industrial requirements. A high power, pigtailed, multi-mode pump module suitable for commercial applications is created through this model. Critical elements are based on telecom architectures, including the optical train and the fiber alignment. The module has a low thermal resistance of 4°C/W from the chip-on-sub-mount to the external heat sink, coupling efficiency of over 80% into 0.2 NA, and demonstrated reliable output power of over 5W cw with peak wavelengths near 915 nm. Individual pump modules are predicted to produce 5W cw output power with an MTBF of more than 400,000h. The relationship between anticipated MTBF requirements, test duration and test population is shown.
Multi-mode pumps based on single emitter diodes deployed in distributed pump architectures offer significant advantages in thermal management and reliability for pumping high-power fiber lasers and amplifiers. In a distributed architecture, while individual diode failures do not directly generate failures of other diodes in the distributed ensemble, failures do cause the rest of the sources to drive to higher power levels to compensate for the loss of power. A model of the ensemble lifetime based on module failure rates and power-scaling factors demonstrates that the distributed pump architecture requires random failure rates corresponding to better than 200,000 h mean time between failure (MTBF) to meet typical application requirements. A high power multi-mode pump module suitable for commercial aplications is shown. Critical elements are based on telecom architectures, including the optical train and the fiber alignment. The module has a low thermal resistance of 4 C/W from the laser diode junction to the external heat sink, couplng efficiency of over 80% into 0.2 NA, and demonstrated reliable output power of over 5W CW with peak wavelengths near 915 nm. Telecom qualified modules have random failure rates corresponding to better than 1,000,000 h MTBF. Stability of the critical fiber alignment joint for single mode packages has been demonstrated at elevated temperatures (e.g. 85 C) for thousands of hours. The reliability of the commercial multi-mode package can be estimated by similarity to the telecom package, and is verified by testing of conditions considered to be at risk based on the differences between the known telecom, and the new commercial package, designs. Test results are shown for temperature cycling, CW operation, and damp heat. The relationships between anticipated MTBF requirements, test duration and test population are shown.