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An asymmetric heterostructure design has been proposed to meet high-power laser diode (LD) requirements, such as a high catastrophic optical damage threshold, a low internal loss, low thermal and electrical resistances and a low vertical beam divergence. The asymmetry has been designed to shift the optical field in heterostructure waveguide toward the n-side, where losses are lower than those at the p-side. The main features of the design are: 1) a thin anti-guiding layer inserted between the “active” [containing quantum well (QW)] and the passive waveguides to elongate field penetration toward the n-side and to increase degree of freedom in design; and 2) reduced p-cladding layer thickness (thanks to the shift of the optical field toward the n-side) aimed at reducing the diode resistances due to shortened QW to heatsink distance. The characteristics of pulsed and CW operation of high-power LDs based on the asymmetric GaAsP/AlGaAs/GaAs heterostructure are presented. A lower temperature increase of the active region of asymmetric LDs compared with equivalent symmetric LDs has been evidenced by time-resolved spectra and thermovision characteristics.