FBH research: 17.01.2018

FBH presents novel pulsed laser sources for automotive LiDAR systems

FBH high current ns laser driver with integrated RW laser diode
Fig. 1: FBH high current ns laser driver with integrated ridge-waveguide laser diode – output power of three emitters is collimated into one spot by optical components from FISBA Photonics GmbH
Experimental power-current characteristics of a DBR BA laser
Fig. 2: Experimental power-current characteristics of a DBR BA laser at temperatures between 15°C and 85°C
Pseudo-color mapping of DBR-BA
Fig. 3: Pseudo-color mapping (red highest, blue lowest intensity) of the lateral profile of the near field intensity of a 50 µm broad DBR BA laser diode (90 A pulse current and about 30 W pulse power)

Lasers generating short optical pulses with a good beam quality and a low wavelength shift over a wide operating temperature are key components for LiDAR (Light Detection and Ranging) systems used in autonomous driving and for object detection. For this application we present broad area (BA) lasers emitting optical pulse powers of tens of watts and pulse lengths in the 10 ns range for wavelengths near 905 nm and environmental temperatures between 15°C and 85°C.

In order to obtain a small wavelength shift with a temperature of 65 pm/K a distributed Bragg reflector (DBR) is integrated into the cavity. For DBR BA lasers with an emission aperture of 50 µm, driven with 10 ns long electrical pulses with a repetition frequency of 10 kHz, optical pulse powers of 34 W at 15°C and 27 W at 85°C are obtained at a pulse current of about 100 A (Fig. 2). Onset of power saturation can be observed beyond 12 W pulse power.

Simulation results of power-current characteristics indicate that the measured power saturation can be attributed less to longitudinal spatial hole burning, but more to two-photon-absorption and gain compression.

At 90 A, the contact mesa with 50 µm width leads to a lateral beam quality factor M2 of about 9 by measurement of the caustics (2nd moments). Its brightness is higher as for the designs with 30 µm and 100 µm  emission apertures.

Streak camera measurements of the temporal evolution of the lateral near field intensity (Fig. 3) reveal that lasing starts at the mesa edges and that the intensity here is higher compared to the middle of the stripe.

In conclusion, internally wavelength-stabilized BA laser diodes with 50 µm aperture widths and an emission wavelength of about 905 nm driven by 10 ns long current pulses reach output powers of more than 30 W with a beam quality factor M2 of 9 at 25°C ambient temperature.

A presentation of the results will be given at Photonics West 2018 in San Francisco.

These research results are part of the PLuS project (Puls-Laser und Scanner für LiDAR-Anwendungen: Automotive, Consumer, Robotic) within "Effiziente Hochleistungs-Laserstrahlquellen (EffiLAS)" in the framework of "Photonik Forschung Deutschland", funded by the BMBF until mid-2019.

Publication:

A. Knigge, A. Klehr, H. Wenzel, A. Zeghuzi, J. Fricke, A. Maaßdorf, A. Liero, G. Tränkle, "Wavelength-stabilized high-pulse-power laser diodes for automotive LiDAR", Phys. Stat. Sol. A (2018) (accepted).