60% Efficient Monolithically Wavelength-Stabilized 970-nm DBR Broad-Area Lasers

Abstract

Progress in epitaxial design is shown to enable increased optical output power P opt and power conversion efficiency η E and decreased lateral far-field divergence angle in GaAs-based distributed Bragg reflector (DBR) broad-area (BA) diode lasers. We show that the wavelength-locked power can be significantly increased (saturation at high bias current is mitigated) by migrating from an asymmetric large optical cavity (ASLOC) based laser structure to a highly asymmetric (extreme-triple-asymmetric (ETAS)) layer design. For wavelength-stabilization, 7 th order, monolithic DBRs are etched on the surface of fully grown epitaxial layer structures. The investigated ETAS reference Fabry-Pérot (FP) BA lasers without DBRs and with 200 µm stripe width and 4 mm cavity length provide P opt = 29 W (still increasing) at 30 A in continuous-wave mode at room temperature, in contrast to the maximum P opt = 24 W (limited by strong power saturation) of baseline ASLOC lasers. The reference ETAS FP lasers also deliver over 10% higher η E at P opt = 24 W. On the other hand, in comparison to the wavelength-stabilized ASLOC DBR lasers, ETAS DBR lasers show a peak power increment from 14 W to 22 W, and an efficiency increment from 46% to 60% at P opt = 14 W. A narrow spectral width (< 1 nm at 95% power content) is maintained across a very wide operating range. Consistent with earlier studies, a narrower far-field divergence angle and consequently an improved beam-parameter product is also observed, compared to the ASLOC-based lasers.

High brightness pumps for fiber lasers based on monolithically grating stabilized diode lasers

“…The chips used for the stack elements consist of two 200-µm stripe width BAL with a 1.0 mm pitch. The resonator length of the chip is L = 4 mm, of which the rear 0.5 mm contains the DBR grating, reduced in length compared to [8], for improved cooling. The DBR used is a surface-etched 7 th -order Bragg grating, as described in [8].…”

“…However, the thin p-side in ETAS designs makes the insertion of a DBR grating technically much more challenging, as the etching depth must be very precise. In spite of this difficulty, when wafer processing of sufficient precision was used, DBR-stabilized ETAS Lasers could be successfully realized, as described in [8]. Specifically, ETAS DBR broad area diode lasers (BAL) with 200 µm stripe and 4 mm resonator length that made use of a 1 mm long rear-facet DBR were demonstrated, that operated with more than 20 W optical power, as shown in Figure 1 b), where the spectral width was 95% = 0.8 nm.…”

“…In the vertical direction, the individual levels are collimated, and sufficient diodes stacked until the beam quality of stack and fiber are matched (allowing for tolerances), to maximize power in the fiber. In the lateral direction, the beam quality of individual 200-µm stripes should be less than half that of the fiber [8] (see also below), so that two stacks of diode lasers can be optically combined and efficiently coupled into the fiber, for power scaling. While first approaches were made with two physically separated stacks of 200-µm emitters delivered to the fiber with a specialized combining element, we were able to further reduce the module size and complexity by using a stack of double emitters with two 200-µm emitters on each stack level.…”

Future for inertial-fusion energy in Europe: a roadmap

“…Europe has an established capability to develop and assemble such light sources for applications that require high output powers with simultaneously high efficiency, such as pump lasers. Diode lasers, that is, single emitters or laser bars, are stacked together to achieve output powers in the kilowatt range, as in the case of the 3.6 kW diode stack developed [ 94 ] by the Ferdinand Brown Institute for pumping Yb:YAG solid-state lasers (see Figure 6(a)). These projects share common objectives with the HiPER+ project in terms of laser development.…”

1550 nm broad area large optical cavity laser with 4.9 W CW output power

“…By optimizing the waveguide structure and in particular the p-and n-doping levels ultra low optical losses could be achieved allowing for increased high optical output power. By integration of an additional DBR grating, wavelength stabilization has been realized [6][7][8].…”