60% Efficient Monolithically Wavelength-Stabilized 970-nm DBR Broad-Area Lasers
P. Crump, Md. Jarez Miah, Martin Wilkens, J. Fricke, H. Wenzel, Andrea Knigge
Abstract
Progress in epitaxial design is shown to enable increased optical output power <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">opt</sub> and power conversion efficiency <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">η</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</sub> 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">opt</sub> = 29 W (still increasing) at 30 A in continuous-wave mode at room temperature, in contrast to the maximum <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">opt</sub> = 24 W (limited by strong power saturation) of baseline ASLOC lasers. The reference ETAS FP lasers also deliver over 10% higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">η</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</sub> at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">opt</sub> = 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">opt</sub> = 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.