PWM-based Mitigation of selected Parasitic Phenomena in LEDs and Semiconductor Laser Devices

Abstract

This PhD thesis presents experimental laboratory-based studies on pulse-width modulation (PWM) as a technique to control changes in emission parameters caused by parasitic phenomena in three classes of semiconductor light sources. The studied devices are automotive light emitting diodes (LEDs) and laser-excited phosphors, high-power visible edge-emitting lasers (EELs), and a large-aperture vertical-cavity surface-emitting laser (VCSEL). Continuous-wave (CW) and PWM operation are compared under matched electrical and thermal conditions. The aim is to assess how tailored PWM drive schemes control optical power, color and spectral shifts, and spatial emission in application-relevant regimes. The results show that optimized PWM can improve chromaticity stability in phosphor-converted automotive sources. Appropriately chosen PWM parameters stabilize spectral and spatial emission in selected EELs and enable more direct control of spectral emission and the far-field pattern in the large-aperture VCSEL. The work also identifies regimes where PWM becomes disadvantageous, including long-pulse operation in LEDs, where the average optical power can decrease, and control of selected non-phosphor-converted automotive LEDs, where PWM offers no clear advantage over CW dimming. These findings are used to define PWM-based control strategies with practical parameter ranges for semiconductor light sources in industrial and scientific applications.