Browsing by Subject "Waveguide design"

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Distributed waveguide design for reducing thermal load in semiconductor high power lasers
(2025-01) Saadi, Osama Aadil
Semiconductor lasers lead laser technology due to their high efficiency, compact size, and cost-effectiveness. Among these, GaAs-based laser diodes (LDs) are the most efficient light sources, but are still constrained by self-heating, which elevates internal temperatures and degrades performance, output power, and de-vice lifetime. Traditionally, increasing the cavity length has mitigated this issue by improving thermal conductivity, facilitated by advances in epitaxial growth, design, and device packaging. However, the cavity lengths of high-power GaAs LDs are now limited to approximately 5 mm, beyond which the output power declines because of intrinsic physical constraints. This work presents a new type of waveguide design, called distributed waveguide (DWG), that overcomes conventional cavity-length limitations. The DWG integrates lasing and secondary sections along the waveguide, which are electrically isolated to control current injection, yet optically connected for efficient beam transport. The laser section is electrically pumped to generate output, while the secondary section operates near-threshold to dissipate heat effectively. Extending the cavity length from 4 to 8 mm, DWG LDs exhibit significantly improved thermal management with favorable device characteristics. Experimental results, corroborated by numerical analysis, demonstrate that DWGs achieve approximately 1.8× lower junction temperature change while delivering high output power. Additionally, the DWG platform and its fabrication process are fully com-patible with standard semiconductor laser manufacturing techniques, ensuring industrial adoption. This work provides clear evidence that innovative waveguide designs can effectively mitigate self-heating, promising enhanced performance, output power, and reliability in semiconductor lasers.
Open Access
Thermal management in high-power laser diodes by waveguide design
(2023-08) Sünnetçioğlu, Ali Kaan
Semiconductor edge-emitting laser diodes (LDs) are known for their high efficiencies but face challenges in managing self-heating at high operating currents and output powers. The excessive heat density experienced by LDs can lead to critical temperature levels, resulting in catastrophic optical damage (COD) and device failure. Understanding the root cause of COD is crucial for enhancing their reliability and operating output power. This thesis investigates the self-heating mechanism in LDs and introduces novel waveguide designs for thermal management. Initially, we experimentally analyzed LDs with varying waveguide widths to uncover the cause of their failure mechanism. Narrower waveguide LDs achieved higher output power densities but maintained lower internal and facet temperatures. The thermal simulation results showed that narrower waveguide LDs exhibit improved three-dimensional heat dissipation, reducing internal and facet temperatures. The results clarified the fundamental reasons behind the superior reliability of narrower waveguide LDs. Next, we designed and fabricated LDs with two different types of waveguides for their thermal management. The first design introduced a two-section waveguide, which moved the laser section heating away from the facet by positioning a window section near the output facet that is pumped to transparency. This approach reduced facet temperature below the laser internal temperature and eliminated the catastrophic optical mirror damage (COMD) failure. The second design, a distributed waveguide (DWG), increased the lateral heat-dissipation area with passive sections between the laser sections. This method achieved LD cooling by effectively dissipating self-heating and reducing the facet temperature. These findings provide valuable guidance for thermal management to realize LDs with significantly improved reliability and lifetime.