Regensburg 2022 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 10: Nitrides

HL 10.2: Vortrag

Montag, 5. September 2022, 15:15–15:30, H34

Short pulse operation of (Al,In)GaN laser diodes to increased linewidth and decreased coherence for laser displays — •Jannina J. Tepaß¹, Lukas Uhlig¹, Dominic Kunzmann¹, Georg Brüderl², and Ulrich T. Schwarz¹ — ¹Institute of Physics, Chemnitz University of Technology, 09126 Chemnitz, Germany — ²ams OSRAM Group, 93055 Regensburg, Germany

Red, green, and blue (RGB) laser diodes are used as the light source in laser displays in particular laser glasses for augmented, virtual, and mixed reality (AR/VR/MR). A narrow linewidth and corresponding high coherence will lead to speckles and non-uniform scattering at the gratings used for the projection into the eye box. Therefore, it is necessary to enhance the spectral linewidth of each laser diode to about 10 nm.

Mode competition causes a dynamic broadening of the laser spectrum already to about 1 nm. Here, we explore short pulse modulation to further increase the linewidth. A wavelength chirp at the beginning of each pulse is generating additional broadening at a pulse length of the order of a few nanoseconds. This chirp is the consequence of overshooting the carrier density above the threshold carrier density, resulting in a blue-shifted gain spectrum.

We investigate these broadening effects in blue and green (Al,In)GaN and red (Al,Ga)InP laser diodes with the help of a streak camera experiment. We took measurements for varying pulse length to analyse the spectral changes of those laser diodes and the behaviour with different pulse length.