Wavelength stabilized high pulse power laser diodes for automotive LIDAR

Abstract

Diode lasers generating optical pulses with high peak power and lengths in the nanosecond range are key components of systems for free-space communication, metrology, material processing, spectroscopy, and light detection and ranging (LiDAR) as needed object detection and autonomous driving. Automotive LiDAR systems demand additionally for a good beam quality and low wavelength shift with temperature due to the wide operating temperature span. We present here internally wavelength stabilized lasers emitting ns optical pulses from an emission aperture between 30 µm and 100 µm with peak powers of tens of Watts at wavelengths around 905 nm. The vertical structure based on AlGaAs (confinement and cladding layers) and InGaAs (active quantum well) is especially optimized for pulsed operation with respect to the implementation of a surface Bragg grating with a high reflectivity. The fabricated 6 mm long distributed Bragg reflector (DBR) lasers are electrically driven by an in-house developed high-speed unit generating 10 ns to 100 ns long nearly rectangular shaped current pulses with amplitudes of more than 100 A. Such lasers emit optical pulses with a peak power of more than 30 W up to a temperature of 85°C with a wavelength shift as low as 65 pm/K and a lateral beam propagation factor down to M²=5. The influence of the lateral aperture width and the pulse length on the beam quality will be shown and compared to spatio-temporal simulations using a model based on the paraxial wave equation for the optical field coupled to a time-dependent diffusion equation for the excess carriers.