New record values for high-current high-speed LiDAR laser drivers
LiDAR (Light Detection And Ranging) sensors have become a fast growing market segment with a broad range of applications, from automotive to robotics. Their functional principle is similar to RADAR but based on light. Hence, because of the shorter wavelength, they provide higher spatial resolution than RADAR, which is essential if a detailed image of the environment is needed.
Most LiDAR system use the pulse radar principle, i.e., they transmit a pulsed signal and detect the arrival time of the echo. The maximum range of operation depends on the available optical pulse power, the range resolution is determined by the pulse width. Typical automotive scenarios, for instance, demand for power levels exceeding 100 watt at pulse widths from 3 to 10 ns. To generate such short and powerful laser pulses, pulse drivers with a peak current value over 100 A are needed. The unique challenge in this time range is handling the parasitic inductances and capacitances in circuit design and the assembly of the laser diode and the driver board. For this purpose, we have developed and patented methods to minimize assembly inductances, mounting the laser diode directly under the printed circuit without using bond wires .
Due to their inherent semiconductor properties, GaN (gallium nitride) transistors offer the best ratio of input capacitances and output current among all technologies so far, enabling to realize the fastest switches in the high current range available today. Since the material additionally features a low on-resistance it is possible to realize very efficient drivers. Our drivers use a GaN device in the final stage in order to allow for optimum high-current switching as well as high efficiency and high repetition rates.
By connecting several driver stages in parallel the output current can be increased with a similar timing behavior like a single driver (Fig. 1). Fig. 2 presents a quadruple driver assembly. On the optical side, the output power of a three emitter array is collimated into one spot by using components from FISBA Photonics as shown in Fig. 2.
One year ago, we have demonstrated state-of-the-art drivers switching 150 A for pulses down to 3 ns. Meanwhile, these values have been almost doubled. The results of a quadruple driver module are plotted in Fig. 3. 100 W optical pulse peak power are obtained in a pulse-width range between 3 ns and 10 ns, with pulse currents between 180 A and 250 A [2,3], which denotes a new record performance. The optical pulses (see inset) have an almost rectangular shape.
These research results were achieved in the course 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 German BMBF.
 A. Liero, A. Klehr, T. Hoffmann, T. Prziwarka, W. Heinrich, "GaN laser driver switching 30 A in the sub-nanosecond range", 46th European Microwave Conference (EuMC), London, GB, pp. 1389-1392 (2016).
 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. Status Solidi A 2018, 1700439, (2018).
 A. Klehr, A. Liero, H. Wenzel, A. Zeghuzi , J. Fricke, R. Staske, A. Knigge, "Pico- and Nanosecond Investigations of the Lateral Nearfield of Broad Area Lasers under Pulsed High-Current Excitation", Proc. SPIE, Photonics West, San Francisco, USA, 101230D (2018).