Waveguide width governs thermal loading and reliability in high-power laser diodes.

A recent industrial trend for high-power laser diodes (LDs) involves widening waveguides to boost output power per chip and reduce cost-per-watt. However, reliable power scaling through this geometric expansion is often limited by thermal constraints. In this work, we present a combined experimental and simulation analysis quantifying the correlation between waveguide width and key performance metrics, including power density, junction and facet temperatures, and catastrophic optical damage (COD) limits. Our results reveal a critical geometric crossover at a waveguide width of W ≈ 50 μm. Below this width, LDs sustain significantly higher output power densities while, counterintuitively, exhibiting lower junction and facet temperatures. Modeling reveals that enhanced lateral heat spreading activates an additional heat dissipation pathway, accounting for up to 35% of the total heat flux in narrow devices. These findings establish thermal geometry, rather than optical power density alone, as a primary determinant of COD robustness and provide design rules for reliable, high-brightness scaling in LDs and arrays.